Jupiter's children go into hiding

The plump moon will stroll by Jupiter tonight and Wednesday night making the planet particularly easy to find. Binoculars and small telescopes will show all four moons tonight but you'll seek them in vain during part of tomorrow night. This illustration and the one below were created with Stellarium.

OK, this is weird. Normally I write about things that might nudge you outside for a look-see but this latest happening is the exact opposite.  It's a total non-event ... in a sense. Tomorrow night (Weds) between 11:43 p.m. and 1:29 a.m. Central time none of Jupiter's four bright moons will be visible alongside the planet. The solar system's father of the sky will be hard pressed to find his children. Just for a little while.

Jupiter in binoculars tonight (Tues.) around 10 o'clock. I've listed the order of its four brightest moons from left to right.

Normally you can see at least a moon or two on either side of the planet. Indeed tonight all four should be visible in a pair of steadily-held binoculars and through any small telescope. Tomorrow night's a different show. For nearly two hours Ganymede and Europa will be in front of the Jupiter and camoflaged from view. You'll need a modest telescope to see them against the pale clouds of Jupiter's equator assuming the air is steady. Io will be tucked behind the planet's edge and then emerge into eclipse, invisible in the planet's shadow. Moon #4, Callisto, will also be in eclipse. If you're used to seeing those familiar little "stars" alongside big, bright Jupiter you might find the moonless view oddly disturbing.

The disappearance of Jupiter's moons is a rare event that happens only about 20 times per century. The last time was May 21 but that one was only visible in the eastern U.S. and for a very brief time. Observers across the U.S. will witness Wednesday night's. Plan your outing well since the show will be over at 1:29 a.m. when Io slides out of Jupiter's shadow and back into sunlight.

A modest telescope at high magnification will show the moon Ganymede and perhaps Europa "hiding" in front of Jupiter at the start of the moonless period. This illustration and the one below are courtesy of Chris Marriott and SkyMap software.

Ready for more? Users with modest-sized telescopes (6 to 10 inches) can enjoy watching the moons Ganymede and Europa and their shadows dot the planet during the moonless time. If you stay up late, you'll see Europa move off the planet's face and shine again in a dark sky. How fine a thing it is to watch this solar system in miniature move with the precision of a classic Swiss watch.

In this view at 1:45 a.m. Central time, both Ganymede (G) and Europa (E) and their shadows are visible through a telescope. The easiest shadow to see is Ganymede's since it's the biggest.

Posted by: rking@duluthnews.com on 8/31/2009 at 8:05 PM | Comments (3) | Permalink

Join me for a lunar challenge tonight

The waxing gibbous moon shines between the leaflets of a fern during twilight yesterday. Photo: Bob King

The sky was hazy last night and the moon low. These two factors combined to give it a pleasing orange color like a ripe peach or cantalope. We see the moon all the time but how many of us have really focused our eyes on it to see the many features presented before us?

Tonight and the next few nights you can use the little chart below to help you identify some of the moon's "seas" as well as one prominent crater. The seas or maria (MAH-ree-uh), which is Latin for seas, are the easiest to find. You probably know a few already since they make up the face of the fabled man in the moon. These grey patches were once thought to be actual bodies of water. We know now that they're large basins hollowed out by asteroid impacts nearly four billion years ago. Not long after, lava welled up from deep cracks and filled the holes with a grey, titanium-rich magma soup which eventually solidified into vast plains.

This photo shows the moon's phase tonight (Monday) and some of the moon's numerous grey patches called maria or seas. Illustration: Bob King

You can see most of the lunar seas with just your naked eye. To give you an idea of which are more challenging, we're going to rate each feature's visibility starting with the easiest and ending with the hardest. Here they are:

1. Sea of Showers
2. Sea of Tranquillity
3. Sea of Serenity
4. Sea of Clouds
5. Sea of Crisis
6. Sea of Fecundity
7. Sea of Nectar
10. The crater Copernicus

Notice that I placed Copernicus three steps below the Sea of Nectar. That's because it's considerably harder to see than the seas and in a class all by itself. Look for a small, isolated white patch between the Seas of Showers and Clouds. Sounds like I'm giving you a forecast, doesn't it? Remember that this is a naked eye challenge, but after you've gone through the list, by all means explore with your binoculars too. Good luck and let us know how it goes.

It's easy to find Venus shining low in the northeastern sky just before dawn (around 4:30-5 a.m. for northern Minnesota and Wisconsin). With binoculars look just to the left of the planet to see the cluster. Created with Stellarium.

Early morning observers can reach for their binoculars the next couple mornings to catch Venus right next to the bright little star cluster called the Beehive in the constellation of Cancer. The contrast between the impossibly bright planet and the tiny cluster stars should make for a very pretty view.

Posted by: rking@duluthnews.com on 8/31/2009 at 9:39 AM | Comments (0) | Permalink

We laud you Henrietta

The three top stars of the Great Square crown the rooftop of a neighborhood house lit by moonlight last night. Details: 24mm lens at f/2.8, 25-second exposure at ISO 800. Photo: Bob King

Chilly last night and great to be out under the stars. The waxing gibbous moon was a studio light in the south bright enough for nighttime portrait work. I grabbed the camera and took this picture of a brick house along my walking path. A couple weeks ago I was struck by how the upper three stars in the Great Square of Pegasus formed a neat starry roof over the earthly one. With the moon for illumination, the photo was easy to shoot.

Have you tried taking photos in moonlight? If not, then get a tripod for that digital camera and wander your neighborhood for places where you can photograph without scaring the neighbors. No one wants a visit from the police in the middle of a time exposure. Set your camera to a higher "speed" like ISO 400 or 800 and make a series of time exposures to see what looks best. The closer to full moon phase, the shorter your times need to be. Moonlight not only provides the light needed to reveal detail in the foreground objects but gives you a rich blue sky background.

We visited Delta Cephei in yesterday's blog and last night I noticed it was a step below its neighbor Zeta. I estimated Delta's brightness at 3.8. I hope you'll be watching with me over the next few nights to see how it fades and brightens again. Delta was the first Cepheid variable star to be discovered and gave its name to the type. All Cepheids experience pulsations and expand and contract like an enormous bellows over a period of days to months (illustration at right).The Cepheids are just one class of variable stars -- stars whose light is not constant but varies.

One hundred years ago, astronomers using trigonometry could measure distances out to only a 100 light years or so. After that they had to rely on shaky estimates. Lucky for them, one Henrietta Leavitt would soon make a seminal discovery that would give us a tool to reach out to the galaxies. Knowing distance in astronomy is crucial because without that bit of information, you can't really know how big or how truly bright something is. Does Vega look bright because it's a gigantic, hot star or because it's close? In Vega's case, the star's proximity is the main reason for its brilliance.

Leavitt (left) worked as a human "computer" at Harvard College Observatory in the late 1800s through the early part of the 20th century. For 30 cents an hour she studied the observatory's photographic plate collection measuring and cataloging the brightnesses of stars. In doing so, she discovered several thousand variable stars, including many in the Large and Small Magellanic Clouds. The Clouds are small, irregular companion galaxies to the Milky visible in the southern hemisphere. In 1908 she noticed a pattern among the Cepheid variables in the Clouds --- the brighter the star, the longer its period. Recall that Delta's period is 5.4 days, the time it takes to go from bright to dim to bright again. Leavitt discovered that the dimmest Cepheids in the Clouds had short periods of around a day or two while the brightest took over one hundred days.

Since all the Cepheids concentrated in the small Clouds were essentially the same distance from Earth, once you knew a star's period you'd also know its true brightness. Leavitt published her findings in 1912. The only thing lacking was the distance to a nearby Cepheid so you could calibrate the scale. Let's say you knew that Cepheid A in the Milky Way had a period of five days, was 120 light years away and of a certain brightness. Now you find a much fainter Cepheid but with the same period. Since you know the distance to the first one, you just compare the difference in brightness between the two to get the distance to fainter, more remote star. If the Cepheid is in another galaxy, once you know its distance you also know the galaxy's. A year after Leavitt published her results another astronomer determined the distance to several nearby Cepheids and got the ball rolling.

The relation between brightness and period is called the Period-Luminosity Relationship and it's one of the greatest discoveries in astronomy. Cepheids are brilliant stellar beacons visible across millions of light years; they provide a crucial yardstick for measuring distances between stars and even galaxies. In quick order astronomers seized on the relationship to uncover the true vastness of the Milky Way. In the early 1920s, Edwin Hubble found the first Cepheids in the Andromeda Galaxy and determined that it was much too far away to be inside the Milky Way as many astronomers believed at the time. Andromeda, thanks to the Cepheids, turned out to be another galaxy altogether over two billion light years from our own. It's no exaggeration to say that Henrietta's careful observation of Cepheids opened our eyes to the true scale of the universe.

Edwin Hubble's photo of the Andromeda Galaxy. Stars marked "N"
are novas (exploding stars). The first Cepheid discovered in the
galaxy is marked "VAR!" at upper right. Hubble originally marked
it as another nova but scratched it out when he realized it was a Cepheid.

(Cepheid animation by Kirk Korista / Western Michigan University. Leavitt photo courtesy of the AAVSO)

Posted by: rking@duluthnews.com on 8/30/2009 at 9:43 AM | Comments (3) | Permalink

A star that just won't settle down

The shuttle Discovery launched successfully last night and is now chasing the International Space Station (ISS). It will rendevous and dock with the ISS on Sunday but I don't have times yet when you might see the two crossing the dawn sky together. If you're one of those planning on watching the ISS tomorrow, you might be the first to know.

In the meantime you can still enjoy the Milky Way and summer stars tonight since the moon's not so bright as to spoil the view. I was out last night around 11 walking the dog and surprised at how bright the Milky Way was. For northern hemisphere observers, the moon is currently near the lowest part of its monthly orbital path through the sky and out of the way.

When I turned north and headed back home, the Big Dipper was low in the northwest and looked lazy like a bear settling in for a long nap. Indeed an inkling of the same might be going on in the heads of real bears as August gives way to September next week. How appropriate that the constellation of the Great Bear is in sychrony with the life cycle of the black bear.

Cepheus the King is Cassiopeia the Queen's husband. They're both near
near the North Star throughout the summer and fall. Our featured star
Delta is marked B and is just off the king's right elbow. Credit: Urania's Mirror

Further up in the northeastern sky was the W of Cassiopeia, now tipped almost on end as if lifted up by helium balloons. From there my gaze floated higher into the realm of Cepheus the King. There at his right elbow I stopped at one of the sky's most famous stars, Delta Cephei (SEPH-ee-eye).

Delta does not jump out at you. It's rather dim and couched next to several similarly bright stars, but keep an eye on it over several nights and you'll see Delta do something very few naked eye stars do: fade, brighten and dim in a regular cycle.

This map shows the sky as you look toward the north-northeast around 9:30 p.m. Delta is at the apex of a compact triangle of stars one outstretched fist above the top right star in the W of Cassiopeia. Maps created with Stellarium.

Delta is the prototype for a class of stars called Cepheid variables. These are unstable giant stars that physically expand and contract. During expansion they brighten, while during contraction they fade. Delta goes through a complete cycle in just 5.4 days, and you can watch the entire huff-and-puff with the naked eye. To help you see the brightness changes we have two able assistants, the neighboring stars of Zeta and Epsilon that together with Delta form a compact triangle. Delta's rise to maximum takes a day and a half while its fall to minimum happens more slowly over four days.

In this closer view, you can see Delta and its neighbors better. Delta's brightness changes are easy to track using Zeta and Epsilon. Don't let the numbers scare you. They're just a measure of brightness that astronomers use called magnitudes. The bigger the number, the fainter the star. The stars in the Big Dipper are magnitude 2; these are about a magnitude or one level of brightness fainter.

Zeta has a steady brightness or magnitude of 3.6 and Epsilon shines at a fainter 4.2. Delta's brightness range of 3.5 to 4.4 fits nearly between the two. Last night Delta was on the bright end of its cycle and almost equal to Zeta. That means that several nights from now, it will be closer to Epsilon. Take a look yourself and revel in the knowledge that you're watching a star physically change right before your eyes. You might feel the same excitement John Goodricke (right) felt when he discovered Delta's variations in 1784 from his home in England. Goodricke was both deaf and mute and died at the young age of 21, but his discovery of some of the first variable stars won him great honors from the prestigious Royal Society of London.

Astronomers have discovered hundreds of stars like Delta since Goodricke's time with pulsation times ranging from a few days to months. One of the most famous is the North Star or Polaris in the Little Dipper. Unfortunately the amount of its variation is so slight we can't detect it with the naked eye. Cepheids, as they're called, range from five to 20 times the mass of the sun and are very brilliant. Because of their predictable variations and great brightness, astronomers discovered they could be used as yardsticks to measure cosmic distances, a key step in our understanding of the universe's true dimensions. It all started with Delta.

We'll look at who made that discovery and how in tomorrow's blog. For more on Delta Cephei, check out this page on the website of the American Association of Variable Star Observers (AAVSO).

(Goodricke portrait by James Scouler)

Posted by: rking@duluthnews.com on 8/29/2009 at 10:26 AM | Comments (0) | Permalink

COLBERT keeps astronauts in good humor

The C.O.L.B.E.R.T decal is placed on the Combined Operational Load Bearing External Resistance Treadmill. Credit: NASA/Jim Grossmann

At 10:59 p.m. Central time tonight the space shuttle Discovery will launch on its next mission to the International Space Station (ISS). In addition to to seven tons of supplies, a load of science equipment and a new crew member to drop off at the station, the shuttle will deliver the COLBERT or Combined Operational Load Bearing External Resistance Treadmill. Yes, it's named after the comedian Stephen Colbert of the Colbert Report. NASA selected the treadmill's name after Colbert took interest in a NASA online naming poll and encouraged his viewers to submit the name "Colbert.”

COLBERT is a high-tech treadmill to help astronauts exercise aboard the station. Exercise is crucial in space to help counteract muscle and bone density loss due to living in a weightless environment. “The main purpose to the treadmill, of course, is to work out those walking and running muscles that would otherwise go unused up here,” wrote Astronaut Ed Lu in one of his Expedition 7 journals in 2003. The treadmill has special monitoring devices that determine if the exercise is having the desired effects. COLBERT's top speed is 12.4 miles per hour but the astronauts will typically be running closer to 4-8 mph.

If you're a regular Colbert Report watcher, I suspect you'll be getting punchy updates on just how well the treadmill is working. And if you'd like to keep a watch for the International Space Station (ISS), here are some morning viewing times. It's unclear just yet when the shuttle will dock with the ISS, but when that information becomes available, I'll update here.

The ISS will look like a bright star traveling from west to east across during the early morning hours. Click here for times for your zip code.

* Saturday Aug. 29 starting at 5:59 a.m. A high, brilliant pass!
* Sunday Aug. 30 at 4:50 a.m.
* Monday Aug. 31 at 5:14 a.m. Another brilliant pass!
* Tuesday Sept. 1 at 4:07 and again at 5:09 a.m.
* Wednesday Sept. 2 at 4:32 a.m.
* Thursday Sept. 3 at 4:56 a.m.

Lyle Anderson of Duluth sent this photo he took early Wednesday morning. While it looks like some kind of UFO, it's actually a time exposure of a low-flying helicopter. The W of Cassiopeia is at center in this fisheye view of the sky.

Posted by: rking@duluthnews.com on 8/28/2009 at 9:42 AM | Comments (0) | Permalink

Polka dots and a suicidal planet

The waxing first quarter moon will shine very close to Antares Thursday evening in twilight. This map shows them at around 8:30-9 p.m. as you look southwest. Created with Stellarium.

The moon will cover the star Antares, the bright red-colored star in Scorpius this afternoon for the Northern Minn.-Wis. region at about 4:05 p.m. Two things will make this nearly impossible to see: bright daylight and the moon's low elevation above the southeast horizon. Skywatchers on the East Coast will have a better chance of seeing the event, called an occultation, through binoculars, or preferably a small telescope, where the moon is higher up.

No matter. The star-moon combo will still be very close together after sunset so keep a lookout for them in the southwestern sky. Many of us get a little thrill to see two bright celestial bodies so close together.

Jupiter wore spots last night (Aug. 26) before midnight. These drawings of the planet's cloud belts and moon shadows were made using a 10-inch reflecting telescope at 250x. "G" stands for the moon Ganymede; "E" for Europa. These two moons and the shadows they cast on Jupiter's clouds made for a wonderful night of planet viewing. In the right drawing, notice how white Europa appears compared to grey Ganymede. Credit: Bob King

I got an unexpected thrill last night when I pointed my telescope at Jupiter. Polka dots! The equatorial region of the planet was spotted with the shadows of two moons -- Europa and Ganymede -- and the little grey disk of Ganymede itself. When a moon passes in front of Jupiter and casts a shadow, astronomers call it a shadow transit. Ganymede, the largest of Jupiter's four bright moons, casts the biggest shadow. You can easily see it in a very small telescope.

The moons Europa (left) and Ganymede taken by the Voyager and Galileo spacecraft. Europa's icy crust makes it one of the most reflective moons in the solar system. Ganymede, which is made of a mixture of rock and ice, is considerably darker. Photos: NASA

What was even more amazing was spotting the tiny white disk of Europa as it neared the inside edge of the planet around 11:30 p.m. It was clearly white in contrast to Ganymede, a testament to its icy surface. It blows me away that even modest telescopes can see such things nearly half a billion miles away. It helped that the air was very steady which allowed the sharpest, clearest views of the planet in a long time.

The show didn't end there. The moon Io popped into view around 11:30 after being eclipsed by Jupiter, and by 12:15 both Ganymede and Europa had departed the disk and sparkled in the dark alongside the planet. Not even Jimmy Fallon could touch this kind of entertainment.

I would posted news of this freckled frenzy in advance but I wasn't paying as close attention to the comings and goings of Jupiter's moons as I should have. The next time Ganymede and Europa cross in front of the planet at the same time will be after midnight on September 3. Please visit back next week when I'll post details.

WASP-18b is so close to the star WASP-18 that it completes one orbit around it in less than a day. Credit: Picture courtesy ESA, NASA, M. Kornmesser (ESA/Hubble), and STScI

There have been more than 370 planets discovered outside the solar system. One of the most recent was picked up by Coel Hellier, a professor of astrophysics at Keele University in England. Called WASP-18b (named after the Wide Angle Search for Planets), this latest find is 10 times bigger than Jupiter and only 1.4 million miles from its star. That's so close that the star's powerful tidal forces -- think of the moon pulling on the Earth to create the tides -- are causing the planet to slowly spiral down into the star. Scientists calculate that this "giant Jupiter" has only a million years to live before it's fried to a marshmallow crisp. WASP-18b is 325 light years away in the southern constellation of the Phoenix. Learn more about fated world here.

Posted by: rking@duluthnews.com on 8/27/2009 at 8:42 AM | Comments (0) | Permalink

Jump on the Jupiter wagon

As August looks to September, the familiar figure of Orion the Hunter gains prominence for early morning skywatchers. This photo was taken today at about 5 a.m. Details: 35mm lens at f/2.8, 25-second time exposure at ISO 800. Photo: Bob King

Orion crept up on me from behind this morning. When I turned from the telescope, I felt the tingle of the Hunter's club raised over my head. Is he back so soon?? The cooler, longer nights have many of us already thinking about fall; seeing Orion at dawn provided even more impetus to relish the ever-shortening days.

Jupiter is one fine bright "star" in the southeast these evenings. Since it's so easy to identify, we're going to put the planet to good use finding several more late summer gems. If you go out around 9:30-10 o'clock and look two outstretched fists to the right of Jupiter, you'll spot two modest stars -- Alpha and Beta in the constellation Capricornus the Sea Goat. The top one is actually a close pair of stars with the designations Alpha 1 and Alpha 2. They look like two beady eyes to me, and you can split them without any optical aid. They're very close but if you stare directly at Alpha, you'll be pleased to see two stars where before you may have noticed only one. 

Jupiter is the brilliant star in the southeast at nightfall. Two fists to the right of the planet takes you to the optical double star Alpha Capricorni. The green circle at right is an enlargement of the Alpha and Beta area so you can better see Alpha as a double. Two fists to the left of Jupiter will take you to a distinctive group of stars that resembles a jumping jack. To the right of the jack are the two brightest stars in Aquarius, Alpha and Beta. The "nebula" shown is described below. Illustration created with Stellarium.

Alpha is an optical double or a chance lineup of two stars widely separated in outer space. Just below Alpha is Beta, a true double star, where both stars revolve about their common center of gravity. You can't split Beta with your eye alone but binoculars will do it with ease. Look for the companion immediately to the right and a bit below bright Beta. Most binoculars will easily show both the false and real doubles in the same field of view. It's a fun coincidence that the two types are right next store to each other.

Now let's swing two fists to the upper left Jupiter to a compact asterism of stars in Aquarius the Water Carrier I've nicknamed the "jack", after the pick-up pieces in the child's game (right). None of these stars is particularly bright but the shape makes it easier to see than you'd think. Whenever you're having difficulty spotting a faint star or stars, look around them rather than straight at them. That way you align the most sensitive part of your retina on the subject. You'll be surprised at how something invisible a moment before will suddenly pop into view.

This photo of the Saturn Nebula was taken by the Hubble Space Telescope. It shows the bright white dwarf at center, ovals of fluorescent gas and two "handles" of additional gas on either side. Credit: NASA/ESA

For telescopes only is the strangely beautiful Saturn Nebula, the shape of which mimics the ringed planet. Also known as NGC 7009, this planetary nebula is 1,400 light years away in the constellation Aquarius. We've looked at planetary nebulas before -- they're the "puffed-away" atmospheres of stars that were once similar to our own sun. A tiny, white-hot cinder of a star called a white dwarf resides at the core of these nebulas and excites the gas around them to glow in psychedelic greens and pinks.

Posted by: rking@duluthnews.com on 8/26/2009 at 12:17 PM | Comments (0) | Permalink

Working on the lunar chain gang

Grey clouds skewer the crescent moon around 8:30 Monday night. Photo: Bob King

I caught sight of the thick crescent moon last night just before a mass of grey cloud covered it for good. Our weather tonight looks much more promising for moonwatching although you'll still need to get out before about 9 p.m. Much later than that and expect to stand on your tippytoes to see it above the treeline.

About two outstretched fists to the left of the moon, Scorpius' brightest star Antares will become visible by mid-twilight. It's nodding off in the west these nights as Sagittarius and Capricornus move in to take over the southern sky. Like kings, queens, presidents and prime ministers, every constellation's dominance is only temporary. Eventually they all move west with the changing seasons and disappear from view.

The moon will be a shiny half-pie Tuesday night in the southwestern sky. You'll find Antares about two fists to the east. Because the moon is traveling a low arc in the west this time of year, it's best to observe it before the end of twilight. Created with Stellarium.

Tonight the moon's terminator, that gently-curved arc that separates the bright, illuminated portion of the moon from the part still in darkness, slices straight across a spectacular trio of craters: Theophilus, Cyrillus and Catherina. The crater rims will glow brilliantly in the early morning sun with bowls still partly steeped in shadow. The terminator is the sunrise line on the waxing moon so anything near it will cast dramatic shadows just as trees and houses do at sunrise here on Earth. The contrast between light and shadow should be strong enough for you to see the crater Theophilus and perhaps the entire trio in a pair of 10 power binoculars. Give it a try and see for yourself. Through a small telescope the chain is one of my top ten coolest spots on the moon.

The striking crater chain of Theophilus, Cyrillus and Catharina will be near the lunar terminator tonight. If you're clouded out, the next two nights should still provide a fine view. Photo: Bob King

Theophilus is named after an ancient Greek geographer and measures 68 miles across. It fairly fresh as lunar craters go, with a sharp-edged rim and a couple of distinctive central mountain peaks. Theophilus overlaps the much older Cyrillus, which is 61 miles across and named for a 4th century theologian. Scientists determine relative crater age by looking at which craters overlap others (the ones on top are younger) and noting how worn or broken their rims are. Cyrillus's rim is worn down and much less crisp than Theophilus to the north. The final crater is the chain, Catherina, named for St. Catherine, a Greek theologian and philosopher, is 62 miles across and even more beaten down than Cyrillus.

So we have a neat sequence of craters tonight that show the march of time in the early history of the moon. If you have a telescope, explore the entire moon to see if you can find other craters which hint of their age by appearance and overlap. 

Theophilus up close and personal from the window of the Apollo 16 command module. Can you spot Cyrillus and Catharina above and to the right? Credit: NASA

Posted by: rking@duluthnews.com on 8/25/2009 at 9:50 AM | Comments (2) | Permalink

Step into the red triangle

Mars, Aldebaran and Betelgeuse form a triangle of similarly-colored stellar orbs in the morning sky just before dawn. This map shows the sky as you look east around 4 a.m. Created with Stellarium.

Early risers can see a red triangle in the eastern sky the next couple weeks as Mars slowly moves among the stars of Taurus the Bull and Gemini the Twins. The little planet teams up with two stars of similar color -- Aldebaran and Betelgeuse -- during the wee hours from 2 a.m. till dawn. Can you see a difference in shading among them? Mars' color comes from iron oxide (rust) in the dust on its surface while the two stars owe their ruddy complexions to incandescent hydrogen gas. The brightest of the trio is Betelgeuse while Aldebaran and Mars shine with nearly equal strength. That will change this fall and winter as Earth's and Mars' orbital motions combine to bring them closer together. Come next January, the Red Planet will shine as bright as Sirius, the sky's brightest star.

Mars photographed through the telescope this past Sunday morning. Three different filters were used and then combined to make the color images at left. The top row was taken at 5:11 a.m Central time; the bottom at 5:31. Photos courtesy of Larry Owens of Alpharetta, Georgia.

That reminds me. If you've been hearing that Mars is making a spectacularly close approach to Earth later this month, it's not true. That's an old Internet news item that's been turning up like a bad penny every year since 2003. Mars is currently far from the Earth and appears like a very tiny gibbous moon in a telescope. Even at high magnification, you'll need patience to see any detail on its surface.

The Block Island iron meteorite is examined by the Opportunity rover on Mars. Credit: NASA/JPL-Caltech/Cornell University/USGS

Better to enjoy the photographs that are being sent back from the Spirit and Opportunity rovers and the Mars Reconnaissance Orbiter. More images have been taken of the two-foot-long Block Island iron meteorite by Opportunity which has cruised over 10.7 miles since landing on the planet in January 2004. Quite a hike for a remotely operated robot. The color image of the meteorite is strikingly clear and shows twisted metal (right side) and pockmarks either from erosion or from melting as it plunged through the Martian atmosphere.

On the left is a closeup photo of the iron crystal pattern in the Martian meteorite; on the right a slice of an iron meteorite found on Earth. They both show a similar triangular structure. Credit: NASA/JPL-Caltech/Cornell University/USGS; NASA

Take a look at that the odd triangular patterns in the closeup photo. Some form of alien writing perhaps? What you're seeing is the Widmanstatten (VID-mahn-Shtett-en) pattern (named after one of its discoverers) formed by iron and nickel that cooled into interlocking crystals 4.5 billion years ago. We see the same pattern in iron meteorites found on Earth. I'd like to be up there at this very moment with saw in hand and specimen bag at the ready.

In this wonderfully evocative photo taken by the Mars Reconnaissance Orbriter, we see a dust devil (right of center) in low-angled sunlight creating a dark trail on the Martian surface. The winds of the dust devil blow away the dust, exposing the dark, subsurface rock. The shadow of the dust devil falls to the right. Credit: NASA/JPL/University of Arizona

Posted by: rking@duluthnews.com on 8/24/2009 at 5:29 PM | Comments (0) | Permalink

Stalled stars and footpaths on the moon

The past two nights have been great for meteor and satellite watching. While there are no regular meteor showers on tap until the Orionids of October, they're always falling from unpredictable places in the sky. The Earth travels at 18 1/2 miles a second as it orbits the sun and is bound to slam into (or get slammed) by asteroid and comet grit along the way.

The Earth's revolution around the sun gives a changing perspective of the sky throughout the year. Our speedy travel causes the stars to drift westward one degree or four minutes of time per day. Illustration: Bob King

We've all noticed that the sun is setting considerably earlier now than a month ago. The length of twilight -- that time of half-light between sunset and true night -- is shrinking as well. These two factors combine to slow down the nightly westward march of the stars. Constellations in the east rise four minutes earlier each night while those in the western sky set four minutes sooner. This drift of the stars is caused by (again) Earth's revolution around the sun. As we travel in our orbit, we look out to see the night sky from a perspective that slowly changes night after night, week after week. Over time, this adds up to a complete change of constellations with the seasons. My favorite analogy is to picture yourself looking out a car window while traveling in a circle, say, around a large lake. You see a different section of the opposite shore depending where you are along the circle.

The moon this evening (Sunday) shortly after sunset. It won't be up for long so try to catch it by 8:30 or so. The star above it is Spica in Virgo but I suspect it might be difficult to see in twilight. Created with Stellarium.

By late August, later sunsets and shorter twilights combine to make night start sooner, temporarily negating the westward drift. You go out to look at the sky when it's dark and for a couple weeks the stars stay nearly put. Tonight however you may notice a new visitor on the scene -- the 3-day-old crescent moon. It's very low in the west-southwest sky 20-30 minutes after sunset. Nice to have the moon back!

In this remarkable photo taken by the LRO of the Apollo 14 landing site, you can actually see the lander and its shadow and the footpath (arrowed) left by astronauts Alan Shepard and Edgar Mitchell as they set up experiments and gathered moonrocks more than 38 years ago in February 1971. Credit: NASA/GSFC/Arizona State University

The moon's been in the news again recently with new photos released by NASA taken by the orbiting Lunar Reconnaissance Orbiter (LRO). The photo above is just a portion of a larger image covering the entire Apollo 14 landing area. While it should come as no surprise on an airless and waterless body like the moon, I can't help but be astonished by how well-preserved the footpath is. Being a walker myself, I feel like I'm right there. In the photo below, again part of the larger image, you can see the track leading almost to the rim of Cone Crater, which Shepard and Mitchell worked hard to reach. They climbed rise after rise and got close but never achieved their goal. Without familiar landmarks and hidden by the upward-sloping land, the crater eluded them. You can now see how tantalizingly close they came. For the complete story and more hi-res photos, visit this website.

This is the other half of the photo shown above. It shows the astronauts' traverse uphill toward Cone Crater. The trek was a grueling one and they had only poor maps. Shepard and Mitchell made it as far as Saddle Rock before turning back. They were just 98 feet from looking right down over the crater rim! Credit: NASA/GSFC/Arizona State University

Posted by: rking@duluthnews.com on 8/23/2009 at 9:17 AM | Comments (0) | Permalink

Tags: astro bob, astronomy, moon

An alien in Cassiopeia? See for yourself

Wheeled by Earth's rotation, stars leave arc-shaped trails as they rise in the eastern sky last night. Details: 11 minute time exposure with a 24mm lens at f/2.8 at ISO 400. Photo: Bob King

While last night's clear sky was perfect for stargazing, it would have been even better to have shared it with my friends at the Chippewa Valley Astronomical Society. They're hosting the annual Starfest weekend from their observatory near Eau Claire, Wisconsin. Work precludes that possibility but I just want to say a big "Hi!" to all you guys. I know you're sitting down by now to blueberry pancakes and sausages after a night that knew no sleep. Tonight looks like another clear one and I'll be out there in spirit with you.

The sky really was fantastic Friday night -- my gosh, the Milky Way looked like a lighted ski trail. I was poking around in the eastern sky with my binoculars and spent some time browsing the cluster-rich constellation Cassiopeia. We keep returning to the famous W for several reasons:

* It's bright and has an easy shape to recognize.
* Within its borders are dozens of star clusters for binoculars and telescopes.
* You can use the W to point you to other interesting places.

Cassiopeia the Queen is an obvious W-shaped pattern of stars about three fists high in the northeastern sky at nightfall. With binoculars, drop down below the left side of Cass to spot the Double Cluster. The "E.T" cluster -- named after the alien in the movie E.T. -- is a misty patch touching a bright star immediately below the W. The top half of the W will point you to the Andromeda Galaxy which is 1-2 outstretched fists to the right. The best time for viewing these delicacies is from 10 o'clock on. Photo: Bob King

We've visited the Double Cluster in Perseus the Hero in a past blog. You can see this double dose of starry richness with your naked eye as puffy patch just below the left side of the W. Binoculars begin to resolve each cluster into individual stars. Very pretty! Now point your binoculars to the star just below the middle of the W as shown on the map above. If you look closely, you'll see a delicate mist or spray of stars called NGC 457. This star cluster is better known as the "E.T" cluster because through a small telescope its two brightest stars look like extraterrestrial "eyes" staring back at the observer. The bulk of the cluster forms a sort of alien torso while two spindly arms of stars seem to reach right out into space on either side of the creature. E.T. is 9000 light years from Earth and contains at least 100 stars.

Can you see the alien in NGC 457? The two stars at top form the eyes and the arms reach out to the left and right. This is how the cluster appears in a modest-sized reflecting telescope. Another nickname for NGC 457 is the Owl Cluster. It's an eye thing. Credit: Henryk Kowalewski

Finally, if you imagine the top three stars of the W as an arrow, it will point you straight down and over to the Andromeda Galaxy. What looks like a spoonful of Milky Way to your eye is 2.5 million light years away, the farthest most of us can see without optical aid. Even from a city's outer suburbs Andromeda is visible on a moonless night, and from the country the galaxy jumps right into your arms once found. Binoculars will expand its size to at least four full moon diameters and reveal a bright, compact center where most of the galaxy's starlight is concentrated. Don't expect to resolve Andromeda into stars anytime soon. Even in big scopes, the galaxy remains as smooth and amorphous as fog.

The Andromeda Galaxy and two of it companion galaxies, NGC 206 (directly below) and M32, the bright spot at the 9 o'clock position from the center. Andromeda is similiar in size to our own Milky Way galaxy. Credit: John Lanoue

We'll be stopping by the Andromeda Galaxy again this fall as it climbs ever higher in the evening sky. Meanwhile, back to enjoying the fine day ahead.

Posted by: rking@duluthnews.com on 8/22/2009 at 9:59 AM | Comments (0) | Permalink

March of the mini constellations

Altair is the bottom star in the Summer Triangle. To find it, look about 3-4 outstretched fists to the upper right of brilliant Jupiter, which catches the eye in the southeastern sky. This map shows the sky around 10 o'clock in late August. All maps created with Stellarium.

The Summer Triangle of Deneb, Vega and Altair is now overhead at around 11 o'clock, and with a week of moonless nights ahead, it's a good time to seek out things that are best seen in a dark sky. I'm thinking here of three little constellations that don't get much recognition from skywatchers. Well, maybe Delphinus the Dolphin does because it's just so cute, but the other two tend to get passed up because they're overshadowed by the Milky Way and whoop-de-doo constellations like the Northern Cross or Pegasus.

From Altair, which heads up the constellation Aquila the Eagle, look a fist above to find the four stars of Sagitta the Arrow. A fist due east of Altair takes you to the distinctive kite-shaped pattern of the dolphin. The faintest constellation of the minis is Equuleus the Little Horse, located a fist below the dolphin.

We're talking about Sagitta (Sah-JIT-tuh) the Arrow, Equuleus (ek-KWOO-lee-us) the Little Horse and the more familiar Delphinus (del-FINE-us) the Dolphin. They march down from below the Northern Cross toward Enif in Pegasus like three floats in a parade. Why not set up a lawn chair and watch them pass by? Just use Jupiter to point you to Altair. Once there, stretch out your arm and use your fist to hop up to the arrow and over to the dolphin and foal.

Here the mythological figures are sketched in to help you visualize the figures the figures the star patterns represent. Notice that Equuleus is right next to the big, flying horse Pegasus.

Some small constellations like Leo Minor and Lynx are relatively new entries in the heavenly lineup. They were created in the 17th century by celestial mapmakers who assembled faint stars between the traditional constellations into new ones. Our three minis however are of ancient vintage and as well known to the Greeks as they are to seekers in the 21st century.

I don't think you'll have a problem seeing Delphinus and even Sagitta, but Equuleus will need more attention since none of its stars is brighter than the 4th magnitude, two levels fainter than the stars of the Big Dipper. If you find all three, please let us know in the Comments section below.

The International Space Station (ISS) continues making fine passes in the early morning hours for our region. The ISS looks like a brilliant yellow star and always travels from west to the east during its passes. Click here to find precise times for your city.

* Saturday Aug. 22 starting at 4:41 a.m. The ISS will pass almost directly overhead and be brighter than Jupiter!
* Sunday Aug. 23 at 5:05 a.m.
* Monday Aug. 24 at 3:58 a.m. (short pass in northeast) and again at 5:30 a.m.
* Tuesday Aug. 25 at 4:21 and again at 5:55 a.m.
* Wednesday Aug. 26 at 4:45 a.m.
* Thursday Aug. 27 at 5:09 a.m.
* Friday Aug. 28 at 5:34 a.m.

Posted by: rking@duluthnews.com on 8/21/2009 at 9:18 AM | Comments (0) | Permalink

Recipe for life may have included a pinch of comet dust

Remember the impact on Jupiter back in July? The dark spot in its cloudy atmosphere was once relatively easy to see but the planet's windy atmosphere has since torn it to pieces. While still visible in amateur telescopes, it's become hard to see at least for observers in the northern U.S., where Jupiter doesn't get high enough to clear the most turbulent air. Many amateur astronomers have been hard at work tracking and photographing the spot in the wee hours of the morning. Some of their images were recently compiled by Theo Ramakers, an amateur astronomer from Georgia and member of the Atlanta Astronomy Club, into this animation.

It shows Jupiter's dark impact spot as you'd see it while hovering above the planet's south pole. Look to the right of center at the 2 o'clock position. From this unique vantage point, we can watch the impact evolve from a simple, dark spot in July to a long line of individual patches.The final photo in the sequence is from August 17. "We believe it was a comet or asteroid measuring perhaps a few hundred meters wide," says Don Yeomans of NASA's Near-Earth Object Office at JPL. "If something of similar size hit Earth—we're talking about 2000 megatons of energy--there would be serious regional devastation or a tsunami if it hit the ocean."

Each pair of photos is a stereo view of Comet Wild 2, a 3-mile-diameter orb composed of ice, rock and dust and strewn with odd-shaped craters and curious mountain spires. You can either enjoy the images straight on or, if you cross your eyes, merge each pair into in 3-D view. Credit: NASA/JPL

Speaking of comets, officials at NASA reported this week that researchers found the amino acid glycine in samples returned from Comet Wild 2 (pronounced "Vilt 2") by the Stardust spacecraft in 2006. Amino acids are the building blocks of proteins, which play key roles in the development and maintenance of all living organisms. One of the most familiar proteins is hemoglobin (left), a complex molecule that carries oxygen from the lungs to other parts of the body. This is the first time an amino acid has been found in a comet and is evidence that some of life's precursor chemicals seeded the early Earth from outer space. Notice I said chemicals. Some scientists believe that life may have evolved elsewhere and arrived on the Earth buried in meteorites and comets. Though that's a possibility, it seems to me that this planet's as good a place as any for chemicals to link together under the right circumstances to form the first wigglies.

In this artist view, jets of gas and dust shoot from cracks and fissures in the surface of the comet. Heat from the sun warms ice inside the comet causing it to vaporize. The vapor breaks through the surface carrying dust along for the ride. Stardust gathered samples of this material during its January 2004 flyby. Illustration: NASA/JPL

Stardust collected dust and gas boiled off the comet's icy core using a unique material called aerogel. Aerogel is a sponge-like substance that's so fluffy, high-speed particles that slam into it get stopped in their tracks without burning up. Stardust returned the samples safely back to Earth in a canister that parachuted down over the Utah desert two years later. Since then scientists have been analyzing a bonanza of very tiny particles, which is how glycine was discovered. For more on the mission, please check out this article or the Stardust website.

Posted by: rking@duluthnews.com on 8/19/2009 at 8:56 PM | Comments (0) | Permalink

A fitful night has me spinning in circles

A series of crude drawings of Jupiter and its moons showing the progress of this morning's eclipse of Europa. Ganymede's light was constant but Europa gradually faded away to invisibility. I hope some of you got a chance to see it. More events like it will happen later this summer. See yesterday's blog for more details. Illustration: Bob King

I had hoped to get to bed by midnight last night but fate intervened. My first mistake was to go out to the country to look at comets and clusters. OK, that was fun. I got home just before midnight and shared a glass of wine with my wife. Since it was now 12:45 I figured why not stay up till 1 to watch Jupiter's moon Ganymede eclipse Europa. Although I was dragging by now, it was really fascinating to see Io slowly disappear and then return to view all in the space of 20 minutes. Time well spent.

Finally, bedtime -- almost. At 1:30 a.m. my daughter informed me she and her friend were going to make scrambled eggs. That was fine but please, keep it down. Ah, sleep! At 2 a.m. the other daughter returned home and woke me up with the closing of various doors. Then just before 3 o'clock I was awakened again by the throb of music. She'd left her stereo on. It was tuned slightly off-station and broadcasting a mix of white noise and sputtering bass. I shut that off and returned once more to the difficult task of a peaceful sleep.

Two days ago when we talked about Draco the Dragon, I mentioned that it, the Dippers, Cassiopeia and Cepheus, along with portions of a few other constellations, are circumpolar for the northern tier of states. Circumpolar means that these stars  are close enough to the North Star to never set. A good rule of thumb to help you figure out what's circumpolar for your city is the height of the North Star above the horizon. It's the same as your latitude. In Duluth, that's 47 degrees. Any star within 47 degrees of Polaris will always travel around it in a complete circle never touching the horizon.

The Earth's north polar axis, shown in blue, points to Polaris (the North Star), while its south polar axis points to the star Sigma Octans for viewers in the southern hemisphere. Seen from the North Pole, Polaris is directly overhead. Illustration: Bob King

The revolving Earth is similar to a spun umbrella. Since our axis points to the North Star, that star remains nearly stationery in the sky while all the other stars describe circles around it. Illustration: Bob King

The number of circumpolar stars or constellations depends upon your latitude. As you travel north of my city in the direction of the North Pole, Polaris moves ever higher above the horizon. By the time you arrive at the pole at 90 degrees north latitude, the North Star is directly overhead. Since the distance between the overhead point and the horizon is 90 degrees, that means that every single star and constellation is circumpolar at the poles. Stars never rise and set -- they remain in their places like good pupils.

This is a view of the entire sky from Duluth, Minn. Stars within the two inner circles are close enough to Polaris to complete their daily circle around the polestar without getting cut off by the horizon. The outer two circles contain stars far enough away from the polestar that their paths are "interrupted" by the horizon. Earth's rotation causes all the stars to complete one circle around Polaris every 24 hours, the length of the day. Created with Stellarium.

From the North Pole, Polaris is directly overhead and all stars describe concentric circles about it without setting. This map shows the sky in mid-October because the sun is finally far enough below the horizon for the stars to come out. You might recall that the pole receives constant sunlight from spring through the first day of fall. Created with Stellarium.

On the other hand, if you travel south of my city, Polaris drops ever lower in the sky until you arrive at the equator where it's sitting right on the horizon. Since Polaris is zero degrees high, there are no circumpolar stars. All stars rise and set (get cut off by the horizon) as the Earth spins on its axis once a day.

Let the stars circle as they want. When darkness arrives tonight, I plan a quiet evening at home.

Posted by: rking@duluthnews.com on 8/19/2009 at 12:20 PM | Comments (0) | Permalink

What dark secret dwells in this cluster's heart?

Storm clouds drift across the northern sky just before sunset yesterday evening. The left side is still lit by the sun while the right is in shadow. Photo: Bob King

Just a few days ago, we looked at the constellation of Pegasus the Flying Horse, which features a large, diamond-shaped asterism called the Great Square of Pegasus. You'll find the Square two outstretched fists below and to the right of the W of Cassiopeia in the northeastern sky at nightfall.

The Great Square is already climbing up the east-northeast sky at 9:30-10 o'clock. Just above the star Enif, the bright cluster M15 beckons binocular users. Maps created with Stellarium.

Dangling like a tasty morsel just beyond the horse's nose is the spectacular globular cluster M15, the 15th entry in the Charles Messier's catalog of clusters, nebulas and galaxies that he saw in his small telescope back in the mid-18th century. M15 is easily visible in 7x35 or 10x50 binoculars as a round, cottony fuzzball tucked into a small triangle of stars. You'll notice right away that it looks different from its neighbors.

Once you find Enif, the nose of the horse, place it at the bottom of your binocular view. Now look up near the top for a tight group of stars, one of which will betray itself as M15 by its soft, fuzzy outline.

A 6-inch telescope begins to resolve some of the cluster's tens of thousands of stars and clearly shows how dense and bright the cluster's core is. In fact, M15 has one of the densest cores of any cluster in the Milky Way galaxy. While the cluster spans some 175 light years, half of all its starry matter is concentrated inside a sphere only 20 light years across at its center. The view of the night sky from a planet revolving around a star in the core must be packed with hundreds of stars brighter than Venus. Its residents would never know a dark night sky.

The gorgeous globular (GLOB-you-lurr) cluster M15 in Pegasus is resolved into a pile of stars when photographed through a telescope. Globulars are named for their globe-like appearance; they're the chandeliers of the galaxy. Credit: Jim Misti

Scientists still aren't sure why M15 has undergone "core collapse". Either the stars have settled at the center through gravity or else there's a supermassive black hole hiding there drawing the stars into ever tighter orbits. If you do get a chance to see this globular cluster in a telescope, the brightest stars you'll glimpse are some 1000 times brighter than our sun. M15 is a cluster of superlatives and one of amateur astronomers' favorites.

You might be able to split Ganymede and Europa around 12:30 a.m. Central time but you'll need very high power. Watch as the two moons separate slightly before the eclipse begins at 1:04 (below). The map shows Jupiter as you'd see it in a reflecting telescope with south at top and east to the right.

For more advanced observers, there's an interesting eclipse happening after midnight tomorrow morning, Weds. Aug. 19. Every six years, Jupiter, the Earth and the sun are lined up so that we see the moons of Jupiter pass almost directly in front and behind one another as they orbit the planet. When a moon crosses in front of another moon astronomers call it an occultation. When the shadow of one moon hides another, that's an eclipse. 

This view shows the planet and moons at 1:10 a.m. Central time when the eclipse is underway. I've drawn the outline of Europa to show you where it is -- you won't actually see it as a circle.

From 12:32-12:48 a.m. tomorrow, the moon Ganymede will occult Europa. Through a telescope, the two moons will be visible as two, closely-spaced separate dots at around midnight, but then merge into a single dot during the occultation. Things get more interesting just 15 minutes later. From 1:04-1:22 a.m., Ganymede will cast its shadow on Europa and make it disappear from view! The eclipse is 99 percent total.

The amazing video at right shows a partial eclipse of Ganymede by the moon Io. Philippine amateur astronomer Chris Go created it by combining multiple photos taken through his telescope.

Sounds like fun tonight if you're willing to sacrifice sleep. If staying up is just not an option, don't sweat it. There will be other eclipses and occultations visible in small telescopes later this summer when Jupiter will be up high during more convenient viewing hours. Please check back periodically for updates. You can also stay on top of the events by visiting this dedicated website.

If you do see the eclipse tomorrow, we'd love to hear how it went. Just use the Comments link below.

Posted by: rking@duluthnews.com on 8/18/2009 at 10:33 AM | Comments (3) | Permalink

Milky Way roadtrip

The Milky Way stands out boldly between the bright stars of the Summer Triangle
last night. Top: Deneb (left) and Vega; bottom: Altair. Details:
16mm lens at f/2.8, 25-second time exposure at ISO 3200. Photo: Bob King

Wow! That's all I could say as I stood under the first dark sky I'd seen in over two weeks. You get used to the light polluted or moon-washed versions and say to yourself "hey, this isn't too bad." Last night neither moon nor city glow had the power to soften the darkness. It was hard, deep. The Milky Way borders were crisp and stood in stark contrast to the background sky.

Time to get outta Dodge. If you haven't taken a drive to the country to see summer's feast of starlight, now's the time to do it. In Duluth, that's about a 20-30 minute drive north of the city. August and September are the very best times to see the Milky Way, the most prominent part of the galaxy we call home. What does it remind you of? The track of a child's muddy shoes, a ribbon to wrap the sky, a silent stream flowing past starry shoals, smoke from a campfire? Analogies come easily when you're staring at over a 100 billion stars.

Draco the Dragon winds between the Big Dipper and the North Star. This map shows the sky as you face north around 9:30 p.m. While Draco has no prominent stars, its shape makes it easier to recognize than you'd think. Created with Stellarium.

I noticed last night that Draco the Dragon is ideally placed in the northern sky. We visited this constellation last spring but it seems worthwhile to return the the dragon's lair once again. Just use the two end stars of the Bowl of the Big Dipper to get started. The first star above the bowl is the dragon's tail. If you're patient and the sky is reasonably dark, make your way stealthfully up the dragon's tail to where it makes a sharp right turn. One outstretched fist later, take a hard left and go straight to the dragon's trapezoid-shaped head.

Here's Draco in the actual night sky. This wide angle photo
squeezes a lot of sky into one frame and was taken about
10:30 p.m. Photo: Bob King

Draco's a huge constellation. Its head reaches nearly to the Vega, which around 9:30-10 o'clock is at the very top of the sky. For the northern U.S., the dragon is one of a handful of circumpolar constellations that wind their way around the North Star and never touch the horizon. Other members in this rather exclusive club include the Dippers, Cassiopeia the Queen and Cepheus the King.

While you're out absorbing photons from the galaxy, take a look to the east and get familiar with the Great Square of Pegasus. Tomorrow we'll visit that constellation's most famous deep sky celebrity.

Posted by: rking@duluthnews.com on 8/17/2009 at 10:57 AM | Comments (2) | Permalink

Star-spangled dawn

Tomorrow morning (Monday the 17th), the moon floats just above brilliant Venus in the predawn sky. This map shows the sky looking east around 4 a.m. local time. Joining the scene are Mars and five bright stars: Aldebaran in Taurus the Bull, Betelgeuse and Rigel in Orion and Castor and Pollux in Gemini. Created with Stellarium.

Just a quick reminder this evening. If you're up tomorrow before sunrise, be sure to look east to catch a fine Venus-crescent moon pairing. Lots of other bright stars will be in the vicinity as well. Truly a star-spangled dawn.

Posted by: rking@duluthnews.com on 8/16/2009 at 9:13 PM | Comments (2) | Permalink

Space station returns plus a big ba-da-boom on the moon!

The sun rises over the Earth's rim illuminating the massive array of solar panels on the International Space Station. Credit: NASA

The International Space Station (ISS) is once again casting its bright eye at the earthbound, this time during the wee hours of morning twilight. Here is a list of passes and times for the Northern Minnesota / N. Wisconsin region. During each pass, the ISS will "rise" in the western sky and move eastward before fading from view. An average flyover takes three to five minutes. Watch for unexpected bright flares off its many solar panels. To find times for your city, click here and type in your zipcode.

ISS passes / all times are Central

* Monday Aug. 17 starting at 5:45 a.m. and moving SW to east. Bright pass.
* Tues. Aug 18 at 4:36 a.m. Brief pass low in the southeast
* Weds. Aug. 19 at 5 a.m. from SW to NE
* Thurs. Aug. 20 at 5:24 a.m. from SW to NE. Brilliant, high pass!
* Fri. Aug. 21 at 4:17 a.m. from SE to NE and again at 5:49 from west to NE. Both excellent.
* Sat. Aug. 22 at 4:41 a.m. from SE to NE. Best and brightest flyover of the week.

In this wide view of the waning gibbous moon, you can just see the pattern of grey, parallel stripes along the moon's limb that define Mare Orientale (MAH-ray OR-ee-en-TAH-lay), the moon's youngest impact basin. See below for a closeup. Photo: Bob King

I saw one of my favorite lunar features the morning of the Perseid shower peak last week. It's a curious pattern of zebra stripes along the extreme southeastern edge of the moon that makes you scratch your head for an explanation. Welcome to Mare Orientale, the Eastern Sea (like the Orient), a now-you-see-it-now-you-don't landmark. The moon rocks back and forth in its orbit as seen from Earth so sometimes this odd pattern disappears behind the moon's edge. Other times, it rocks back into view. Mare Orientale is currently well-placed for low power telescopic viewing around the time of the moon's last quarter phase through the remainder of summer and fall.

In this closeup, you can see the Mare much better. The lunar sea or basin is named for its location along the moon's eastern edge. The bright, fresh crater Tycho is also shown. It only takes a little imagination to see the stripes as part of the larger bullseye impact pattern. Photo: Bob King

No one knew for sure what there weird stripes were until the 1960s when astronomer Gerard Kuiper (KYE-per) projected images of the area onto a spherical globe and suspected he was seeing a large, multi-ringed impact basin. An impact basin is the same as a crater but on a scale so much larger that instead of one simple rim, basins have multiple concentric rims or rings. Because the Eastern Sea straddles both the near side and the far side of the moon, we only get to see a very foreshortened view of half the basin. To see it in its glory you either have to go there as an astronaut or send a satellite to take photos from orbit.

The bullseye Mare Orientale is near the center of the moon in this photo taken by the Galileo spacecraft during one of its Earth flybys en route to Jupiter. The sun is shining straight down on the basin so it doesn't show much relief. The dark lava stripes to the upper right of the basin's center are the same ones that show along the edge of the moon in the photo above this one. It's fun to compare them. Credit: NASA

In 1967, Lunar Orbiter 4 sent back the first clear photos of the gigantic impact. The image still wows me to this day. That bullseye you see is 600 miles across and was created by the impact of an asteroid-sized object that crashed into the moon some 3.8 billion years ago. What an cataclystic event to have witnessed from the early Earth! The strike was so powerful it created molten ripples of rock in the lunar crust which cooled into a series of concentric rings. Later, lava from deep within the moon poured out through fractures in the tortured crust, forming dark pools between the lighter mountainous rings. It's these now hardened pools, greatly foreshortened, that we see as dark stripes along the moon's edge. Thanks to photos from the lunar orbiters we can now truly appreciate what those skinny zebra stripes represent.

I saved the best for last. With sunlight coming in at a low angle, you can really see the texture and contours of the rings as well as appreciate the bullseye pattern. Most of the large, dark spots on the moon's near side were also formed by asteroid-sized impacts but Orientale is the freshest one. Photo by Lunar Orbiter 4. Credit: NASA

In a twist of irony, Mare Orientale is now located on the far western side of the moon. Come again? In 1961 the International Astronomical Union re-named the lunar directions after how an astronaut on the lunar surface would orient him or herself, rather than how we see the moon in our sky on Earth. That changed the east edge of the moon to west. Either way, Mare Orientale will never lose its impact.

Posted by: rking@duluthnews.com on 8/15/2009 at 3:01 PM | Comments (0) | Permalink

How Io helped us clock the speed of light

Earth, Jupiter and the sun are all in a line in mid-August as Jupiter reaches its opposition point. The planet is about 375 million miles from Earth or 186 million miles closer than when our planet is on the other end of its orbit. Illustration: Bob King

Jupiter was at opposition to the sun yesterday and at its closest to the Earth for 2009. All the outer planets orbit the sun more slowly than the Earth, so each year our swifter planet swings between them and the sun to create a compact planetary lineup. It happened with Jupiter on the 14th and will again with distant Neptune next Monday the 17th.

Since Earth is on the same side of the sun as Jupiter, we're considerably closer to it than when we're on the opposite side of our orbit. Closer means brighter and brighter catches our attention. This particular opposition is the closest one so far this century; Jupiter is brighter than it's been for years. Since the planet is directly behind Earth (see diagram), it appears "opposite" the sun in the evening sky, rising at sunset and setting at sunrise. Hence the term opposition. The photo of Jupiter at left was taken just yesterday by astrophotographer Christopher Go and shows the planet's cloud belts and the Great Red Spot.

It's fun to think how far away Jupiter is in terms of delay time for communications. If you were standing on one of the planet's moons (Jupiter has no hard surface) and I radioed you a a big "howdy" at the speed of light, it would take just over 33 minutes to arrive in your earphones. Your reply of "wish you were here" would take another 33 minutes to get back to me.

By late next January, when Earth and Jupiter are on opposite sides of the sun, the time lag will have increased to 50 minutes for a one-way trip. This change in Jupiter's distance from Earth allowed early astronomers to make the first real estimate of the speed of light.

In the late 1600s, Danish astronomer Ole Roemer (right) observed Jupiter's bright moon Io as it was regularly eclipsed by the planet's shadow. Since Io travels in a circular, repeating orbit around Jupiter, it was easy enough to predict exactly when the eclipses would happen. But as Roemer continued to follow Io month by month, he noticed something odd. There would be a stretch of several months when Io would go into eclipse earlier than predicted, followed by a stretch when the eclipses lagged behind the predicted times. In fact, the time between successive eclipses became shorter as Earth approached Jupiter and longer as Earth moved away. Roemer correctly deduced that the difference in times was due to light taking longer to arrive at Earth when Jupiter was farther away than at the time of opposition.

Based on Roemer's data and approximate distances to the sun and planets, astronomers at the time determined that it took light a little more than 16 minutes to travel from sun to Earth. Since Earth is about 93 million miles from the sun, a simple division calculation puts the speed of light at around 131,000 miles per second. With improved information on the size of Earth's orbit, his calculations were later refined to "7 or 8 minutes" travel time or very close to the current 186,000 miles per second. Roemer was clearly in the ballpark.

All that just by paying attention to the comings and goings of a single moon of Jupiter. Keen observation and a willingness to follow up on nagging details like out of whack eclipse timings led to a most unexpected and welcome discovery.

Join Ole Roemer in spirit tonight by pointing your binoculars or small telescope at Jupiter, that bright beacon of light in the southeastern sky around 10 o'clock. All four moons are out once again: 1 = Europa, 2 = Ganymede, 3 = Io and 4 = Callisto. Created with Stellarium.

Others before Roemer, including Galileo, had tried to figure how fast light traveled but could only say it was significantly faster than the speed of sound. Light travels fast! That's why you need great spans of space -- like an Earth-Jupiter distance -- to get a grip on its cheetah-fast beams. Go out tonight, gaze at Jupiter and feel for yourself the gulf light has to travel to reach your eyes.

Jupiter's moon Io, the most volcanically active body in the solar system, is seen here
revolving on its axis while rotating around Jupiter. Io is 2,255 miles across, nearly
the same size as our moon. Many of the dark patches are active volcanoes.

Posted by: rking@duluthnews.com on 8/15/2009 at 8:50 AM | Comments (0) | Permalink

Just horsing around plus readers' photos

Lyle Anderson of Duluth was trying out his new fisheye lens converter when he caught a Perseid brighter than Venus Tuesday night. "My guess is that it was around mag minus 6 or 7 when it was at its brighest, and traveling from a north to south direction," said Anderson. "It was a real smoker." In the photo, the W of Cassiopeia is just left of center. Details: ~ 3 minute time exposure at ISO 200. Credit: Lyle Anderson

Dave Ulrich was out Wednesday night shooting Perseids. "I kept shooting random shots of the sky with my little Kodak Easy Share Z8612 hoping to get lucky," said Ulrich. After no success, he decided instead to photograph Jupiter. "In the middle of a 10-second exposure, one of the brightest meteors I saw all night blazed right through the frame!" Credit: Dave Ulrich

We received several fine photos from our readers of this week's astro highlights. The meteors in the pictures were both "fireball" status, meaning they rivaled Jupiter and Venus in brightness. Those who photographed the Perseids discovered that you have to shoot a lot to capture just one or two. Good meteor photography involves a good measure of luck. Thank you very much Lyle, Dave and Jim for sharing your images with us!

The last quarter moon was smack dab in the middle of the Pleiades star cluster this morning. "The occultation was neat and it was amazing to see the moon overtake the bright stars," said Schaff. Details: 1 second exposure at 300mm focal length at ISO 400. Credit: Jim Schaff

Anyone get up to see the moon hide the Pleiades this morning? At least one person did -- Hermantown's Jim Schaff. Jim just returned from a long trip with a major case of jet lag. For once, jet lag was useful because Jim found himself awake at 3 in the morning when so much was happening this week. He made good use of his time by watching the meteor shower and photographing this morning's Pleiades occultation.

The Great Square, located well below and to the right of Cassiopeia, is just a portion of the larger constellation of Pegasus (PEG-uh-suss). Need a little help seeing a horse among its stars? Check the mythological map below. All maps created with Stellarium.

About two weeks ago we took a look at the Great Square of Pegasus ascending in the eastern sky at nightfall. I thought it would be fun to get familiar with the rest of Pegasus the Flying Horse. Once you've located the Square, look above and to the right of the star in the right corner. You'll spot two fainter stars that lead you to brighter Enif (EE-nif), which represents the horse's nose. The two front legs are outlined by a small group of stars directly above the topmost star in the Square. Now can you see a horse?

The mythological figure of Pegasus is drawn in to help us to picture a flying horse among its dozen or so stars. Also take note of Andromeda the Chained Princess to the left of Pegasus, and Cassiopeia the Queen, who's admiring her reflection in a mirror.

Arcturus is one of the brightest stars in the spring and summer sky and easy to find just by following the arc of the Big Dipper's Handle.

At the same time that Pegasus, a constellation of the fall sky, rises in the east, the spring constellation of Bootes begins its descent in the west. Its brightest star, Arcturus, is the only bright red-tinted star in the western sky at dusk. It lies off the Handle of the Big Dipper. Once you've found Arcturus, see if you can follow the dotted outline in the map to take in the whole constellation of Bootes the Herdsman.

The Herdsman is on to greener pastures as summer turns to fall. Meanwhile, the winged horse rises ever higher on the autumn winds.

Posted by: rking@duluthnews.com on 8/14/2009 at 11:53 AM | Comments (2) | Permalink

Seven Sisters minus three

Based on e-mails and comments I've received, the Perseids were still slamming away last night, although at a lower rate than the morning before. A trickle of meteors will continue brighten the heavenly dome for the next few nights. Now that the moon rises later, we have longer hours of darkness, perfect for watching meteors, satellites and the Milky Way. If you see a meteor that doesn't trace its path back to Perseus, don't be surprised. From a dark location, an average of seven sporadic meteors per hour appear on any given night. They're a normal part of the celestial scenery.

Through a pair of 7-10x binoculars, you can spot up to four of Jupiter's brightest moons. This is the view tonight around 10:30 p.m. tonight when they'll all be lined up on the right (west) side of the planet. The moons look like tiny stars. In reality, each is about the size of our own moon. From left: 1 = Io, 2 = Europa, 3 = Ganymede and 4 = Callisto. Diagram and maps created with Stellarium.

Jupiter is sure amazing, isn't it? Shining away in the southeastern sky at nightfall, it looks a lot like a airplane light. Try pointing your binoculars at the planet to see how many moons you can spot. If you focus carefully and support the binoculars on a tripod or, like I do, wedge yourself against the side of a building, you might see all four. For clarity, the diagram shows the moons more spread out than you'll actually see them. Look for the four to be in a more compact arrangement closer to the planet. Because they're revolving around the planet, each with its own period, their arrangement tomorrow night will be completely changed. You've got to see it to believe it.

Ready for another predawn outing? I know you're in shape now after passing time with the Perseids. If so motivated, you can watch the last quarter moon slowly glide through the heart of the Pleiades star cluster, more familiarly known as the Seven Sisters. The cluster is prominent in the late autumn and winter evening sky but makes its reappearance in the morning sky during mid-summer.

If you go out Friday morning (Aug. 14) at around 3, you'll see the moon parked right next to the Pleiades. Its light might make the cluster tricky to see but avail yourself of binoculars and you'll get a great view.

Tomorrow morning beginning around 3:30 Central time and continuing through dawn, the moon will occult three bright members and numerous fainter ones in the cluster. An occultation occurs when the moon passes in front of a star or planet and blocks it temporarily from view. For the upper Midwest, Maia (MY-uh) will hover along the moon's bright edge and then disappear about 3:30; Merope (MARE-oh-pee) at 4 and Alcyone (al-SIGH-on-nee), the brightest of the Pleiades, at about 4:30.

Two views of tomorrow morning's occultation as you'd see it in binoculars. At 3, the moon will be to the right of the Seven Sisters cluster, while by 4:30, it will have moved to the center. The moon's orbital motion carries it eastward at the rate of one full moon diameter per hour.

While the sight of the moon smack in the center of a familiar star cluster is very cool, to really see the occultations, you'll need a small telescope. Then you can watch Maia and the rest poised along the moon's bright edge before they're overtaken by its advance. A star's disappearance is a sudden, split second event that may surprise you. The moon has no atmosphere to slowly dim the star's light, so one moment it's there and the next it's gone. Be sure to watch for the reappearance of the brighter stars along the moon's dark, unlit edge too.

Keep in mind that the moon's path and the times listed are for the N. Minn/N. Wisconsin region. The moon's path and disappearance times will be somewhat different if you live well outside that area.

Tomorrow we'll return to more pleasures and treasures of the evening sky.

Posted by: rking@duluthnews.com on 8/13/2009 at 10:44 AM | Comments (2) | Permalink

Ridin' the meteor train from dusk till dawn

Orion the Hunter rises over the house around 4:30 this morning. You can spot his three Belt stars just to the left of the rooftop. Winter creeps back just as summer reaches its peak. Details: 35mm lens at f/2.8, 18-second exposure at ISO 800. Photo: Bob King

I should be stumbling around today after a two-hour, predawn stint with the Perseid meteor shower but I'm still smilin'. Not that there were that many shooting stars in the end. I saw two nice ones Tuesday night in an otherwise slow showing before midnight. This morning was definitely better. I set up a sleeping pad and pillow on the driveway, placed the camera on a tripod next to me and every so often reached up to squeeze the release and take a picture.

My first Perseid of the morning flashed near the W of Cassiopeia about 3:05 a.m. Details: 24mm lens at f/2.8, about a 1-minute time exposure at ISO 400. Photo: Bob King

The morning was pleasant, about 60 degrees, with a gently breeze and no bugs. The thing that struck me most was how swift the Perseids were. An old friend once called them "javelins of light" and I had to agree with that description. They were white, piercingly fast and about half a dozen left lingering trails. I faced north where I could avoid the glare of the moon and saw some 28 Perseids during the hour from 3 to 4 a.m. Several more later brought my total count to 34 ... plus one bat (a dark meteor of sorts).

Of the 63 images taken, only three held meteor treasure. These three were all bright to eye but because they were so swift, appeared fainter in the photographs. No glaring fireballs were seen. In the end, I thought the shower was rather tame, no doubt in part because of the moon.

Another swift Perseid slices through the Northern Cross in the western sky around 3:30 a.m. Details: same as above but a 2-minute exposure. There was a definite increase in the meteor rate when we passed though the "dust filament" between 3 and 4 a.m. After 3:50 a.m., I noticed that the rate fell off. Photo: Bob King

Yet moonlight was welcoming, and the quietude of the night soothed all anxieties and concerns that normally occupy our heads during the day. Since you never knew when the next one would appear or how bright or faint it might be, every single meteor was special, a small gift.

I hope you enjoyed your Perseid experience, and if you'd like to share it with our readers, just click on the Comments link below. For those who were clouded out, you can try again tonight. Thought the rate will likely be lower, the shower will still be active over the next several nights so it's worth another look. ** UPDATE 4:30 p.m. Weds. New information indicates that the shower might more active than originally expected this evening (Weds.). Keep a skyward eye when darkness falls. **

Tomorrow we'll use your new-found ability to arise before dawn to look at another special event coming up on Friday. See you then.

Posted by: rking@duluthnews.com on 8/12/2009 at 12:26 PM | Comments (6) | Permalink

Camera tips for shooting the Perseids

Tonight's the night of the Perseid meteor shower, and by some stroke of luck the forecast for the Upper Midwest is for clear skies. I plan on setting the alarm for 2 a.m. to catch the "normal" maximum of the shower and then the spike that's predicted to begin an hour later (see yesterday's blog for more information). I hope your weather looks as good as ours.

A modest digital camera mounted on a tripod. A sturdy mount or platform is essential to taking astrophotos. Photo: Bob King

If you'd like to try photographing the shower, the two things you need are a camera you can manually set to take a time exposure and a tripod to mount it on. Inexpensive point and shoot digital cameras will allow you to expose up to 15 seconds or so, but that's barely enough. With a a slightly higher-end camera you can set the exposure for as long as you like. Long exposures are necessary to record stars and to increase your chances of snagging a meteor.

Mount your camera on a tripod so it doesn't shake as you're taking pictures. If you don't have one, prop it up with books or wood on your driveway. If you're really desperate, as I was once when photographing northern lights on a camping trip in Alaska, place a flat object like a tray or bucket right on the lawn, and lay the camera on top with the lens facing straight up. There's always a way.

While it's nice to have a cable release -- a device that lets you press the shutter button and keep it down without touching the camera -- it's not essential. You can carefully hold the button down for a minute or so with your index finger.

OK, so you've got the camera and, hopefully, the tripod. Next, dial up your "film speed", now called ISO, to 400 or even better, to 800. The higher the number the greater sensititivity to light. If you go too high though, your photos will look grainy or "noisy". If you're using a point and shoot variety camera, turn the top dial to the Tv (shutter speed priority) setting and set the exposure to at least 15 seconds. On the higher-end models, adjust the time manually to between one and five minutes and open your lens to its widest setting, usually f/2.8 or 3.5. Night sky photography requires wide-open lenses to gather as much light as possible.

Still with me? Good. There's one last step before you can start shooting. If you can, take your lens out of autofocus mode and click it into manual. Autofocus sometimes has a hard time focusing at the empty sky. Once you're set to manual, focus the lens to the infinity position which is marked by a sideways "8" on the barrel.

The best lens to shoot meteors is what you normally use to shoot during the day -- 24-35mm (wide setting) up to 50mm. I like to aim my camera up in the northeastern sky above Perseus or over to the south or even overhead. With the moon out for this year's shower, you won't be able to take especially long exposures without overexposing your pictures. Try shooting a few one to two-minute time exposures, then some at three, four and even five minutes at ISO 400 to 800. Take a look at the camera back on the replay to make sure you're in the ballpark. If you don't see any stars in your pictures, increase the exposure time. When the moon's in the sky, take your longer exposures well away from it, otherwise your pictures will be overexposed.

A whole new cast of characters comes up in the east tomorrow morning just before twilight begins. Six bright stars and two planets will lead the show. Venus is the brightest of them all. Created with Stellarium.

The more you shoot, the higher the odds you'll nail a Perseid, but don't miss the chance to just kick back and look up. A bunch of new constellations adorn the midnight and morning sky. Jupiter will blaze in the south all night. If you stay up really late, you'll get a sneak preview of the winter constellations and a peak at the planets Mars and Venus. Yes, even the mighty hunter himself, Orion, finally pokes his head over the horizon just before dawn.

By all means, we'd love to see your photos (send e-mail to: rking@duluthnews.com) and hear your reports (use the Comments link below). Good luck!

Posted by: rking@duluthnews.com on 8/11/2009 at 11:01 AM | Comments (6) | Permalink

Dust turns to fire Tuesday night

A Perseid meteor creates a bright trail of light as it burns up in our atmosphere. Credit: Copyright T. Credner and S. Kohle, AlltheSky.com

Ever get a rock in your shoe? You stop, unlace and tip your shoe out. The rock that falls to the ground is usually very small. Hard to believe that thing caused you so much grief. Tiny nuggets like it will flash through the sky Tuesday night / Wednesday morning as the annual Perseid meteor shower, one of the year's most reliable, returns again. The meteors range in size from sand grains to garden peas and are debris shed from Comet Swift-Tuttle during its repeated passes through the inner solar system. Tuesday night (Aug. 11) the Earth's orbital motion around the sun takes it straight into the wake of the comet. We'll look up and watch those bits of Swift-Tuttle collide with the upper atmosphere at 130,000 miles per hour. At such a tremendous speed, they vaporize in a second or two, sometimes leaving persistent, glowing trails called meteor trains. Matter of fact, the Perseids are known for their trains. They remind me of chalk streaks.

As Earth heads into the Perseid stream Tuesday night, the meteors will appear to radiate from a point in the constellation of Perseus the Hero just below the W of Cassiopeia. This perspective effect is similar to driving into a snowstorm -- remember those? All the snowflakes appear to radiate from a point right in front of you. Illustration created with Stellarium.

Meteor showers are a joy to watch because they require no special equipment. Find a place with a reasonably dark sky and spread a blanket on the ground and one on yourself to keep cozy during the damp night. If you can coax a friend to stay up with you, all the better. With a thermos of your favorite hot beverage on hand, you're ready to go. Although the meteors appear to radiate in the northeast, they'll streak across all parts of the sky. My favorite position is facing east. That way you get to see the short ones near the radiant plus the long, streaky ones overhead.

Timing is important. A smattering of Perseids have been flashing around for the past two weeks but the peak will occur early Wednesday morning the 12th. The later you stay up, the higher the radiant and the more meteors you'll see. The Perseids usually spit out about 60 per hour on a moonless night from a dark location, but this time around the waning gibbous moon will join the party and spoil things a bit. Its glare will reduce the number of fainter meteors but that's no reason to cancel a perfectly good pre-dawn outing. We should still see at least 30 per hour.

A sequence of photographs of Comet Swift-Tuttle showing its bright star-like nucleus (left) and dusty tail. Inside the bright part is a hunk of dusty ice about six miles across. Heat from the sun causes the ice to vaporize and release its dust into the tail. Some of this material burns up as Perseid meteors some 70 miles over our heads every year in mid-August. Photo credit: Spacewatch Program, LPL, Univ. of Arizona

Ah, and there is a nice surprise awaiting those who do there watching between 3 and 4 a.m. Central time Wednesday when the radiant is highest just before dawn. According to NASA's Meteoroid Environment Office, Earth will blast through a thicker filament of dust shed by Swift-Tuttle in 1862 at that hour. Double the normal rate is expected!

Once again, here's what you need to know:

* Get comfortable -- find a spot where you can lie down and face east or south.
* Allow your eyes at least 10 minutes to get adapted to the dark.
* Plan on spending at least a half hour with the shower. Sometimes there are five minute or longer gaps when no meteors appear. Other times, you'll see several within seconds of each other.
* If you go out Tuesday before midnight, you'll definitely see some Perseids but not the peak of the show.
* For early morning viewing, don't forget to set your alarm for around 2 or 3 a.m. Wednesday Aug. 12.
* Just for fun. see if you can trace the paths of the meteors back to Perseus in the northeast.

Tomorrow I'll provide a few tips on how to capture a souvenir Perseid with your camera.

Posted by: rking@duluthnews.com on 8/9/2009 at 5:11 PM | Comments (1) | Permalink

My dog eats berries

Sammy happily eats the fresh raspberries she's offered. She also enjoys blueberries, strawberries and dewberries. Photos: Bob King

Like most dogs, Sammy enjoys eating just about anything so I really shouldn't be surprised that she likes berries too. Maybe what tickles me is the delicate, almost humanlike way she pulls them into her mouth. While I pick, she watches but rarely goes foraging for them herself. Then when I'm ready to share she sits at attention and eagerly laps the fruit down.

Berries seem to be the theme this weekend. My wife and I picked rain-soaked blueberries Saturday. We cleaned 18 lbs. of purple spheres and set them in trays and pans overnight to dry. When I awoke this morning, I discovered a fun surprise from my younger daughter. She'd been up earlier and had sampled berries from each tray. In one she spelled out exactly what she thought about the harvest.

A message in blueberry script from my younger daughter Sunday morning.

Several years ago, the Opportunity Rover discovered immense numbers of "blueberries" on Mars. I'll never forget how surprised I was to see the first photos of these perfect little spheres (right), most of them only 4-5 mm or about 1/5" across. More like BBs than blueberries but the name stuck. The little balls are technically called "hematite concretions" and formed underground when minerals precipitated from flowing groundwater. As water flowed through and around layers of rock, chemicals in the water caused iron minerals settle out in the form of small, BB-like balls. Even before they were discovered, scientists at the University of Utah predicted they'd be there. They'd studied similar concretions that were strewn about the rock formations of southern Utah.

Martian blueberries, sadly not edible, are scattered among eroding rocks in Meridiani Planum on Mars. Photo taken by the Opportunity Rover. Credit: NASA

Each rover is equipped with an instrument that can "sniff" out the composition of nearby rocks. When Opportunity got up close and personal with the blueberries, it discovered they were made of nearly pure hematite (HEEM-uh-tite or HEM-uh-tite), an iron oxide similar to rust. Hematite almost always forms in the presence of water and likely indicates that groundwater flowed freely beneath the surface of Mars. Erosion later removed the softer, surrounding rock, leaving the harder blueberries to litter the surface. Future astronauts better watch their step when explore these little buggers. It could be like walking on marbles. (The photo at right shows Martian blueberries eroding out of a rock outcrop.)

Wherever we find water on our planet, we find life. These hard little blueberries are just one more indicator that Mars may have once been more Earth-like. Scientists suspect there may still be underground water and even hot springs on the Red Planet today. Can't you just imagine acidic waters bubbling away just beneath the surface, working on a new crop of blueberries? And while the Martian variety aren't the kind that make you say YUM!they're no less a bountiful harvest.

Marble-like rocks known as hematite concretions litter the surface of Navajo sandstone at Grand Staircase-Escalante National Monument in southern Utah.The rocks accumulated after softer surrounding sandstone eroded away. They are similar to the "blueberries" found on Mars by NASA's Opportunity rover. Credit: Brenda Beitler, University of Utah.

Posted by: rking@duluthnews.com on 8/9/2009 at 8:55 AM | Comments (7) | Permalink

What's hiding inside Saturn's rings?

Because Saturn's axis is tipped like the Earth's, as it revolves around the sun in just over 29 years, we see the rings open and close. When the rings are edge-on to our view, Saturn is at or near one of its equinoxes. This happens approximately every 15 years.  Illustration by Hui Chieh and used with permission.

Saturn revolves around the sun once every 29 years, and because it's axis is tipped almost 27 degrees (just a little more than Earth's), it experiences seasons. First one hemisphere and then the other is angled toward and then away from the sun, creating the familiar rhythm of high sun (summer) and low sun (winter). Since our planet takes just one year to complete an orbit, a season lasts a quarter of that or three months. Saturn takes 29 times as long to make the same journey, so each of its seasons lasts over seven years.

On Earth, the sun hovers directly over the equator only two times a year at the spring and fall equinoxes. The same is true at Saturn but because of its longer year, this only happens twice every 15 Earth years.

Saturn's rings are some 175,000 miles across but only some 30 feet thick. In early August the sunlight just grazes the ring plane, causing anything poking above the rings to cast a long shadow. Illustration credit: NASA/CXC/M. Weiss

After a nearly 15 year wait, equinox time is fast approaching for the ringed planet as well. On August 11, the sun will shine straight over Saturn's equator. Since the rings circle the planet in the same plane as the equator, sunlight will skitter across them at a very shallow angle. Any structures or tiny moons poking the smallest amount above the plane will catch the low sun and cast long shadows. Ever notice how even small things like gravel and grass cast considerable shadows near sunrise or sunset? The same thing is happening almost a billion miles away at Saturn. Low sun angles bring out details and features that would we'd otherwise never see.

So what might Saturn's rings be hiding? The Cassini spacecraft has been watching the planet intently this summer making the most of the low sun. Below are several remarkable photos of teeny, tiny moons and their shadows as well as one unknown "structure" found in Saturn's F ring.

The Cassini spacecraft captured this image of a small object in the outer portion of Saturn's B ring casting a shadow on the rings as Saturn approaches its August 2009 equinox. The shadow length implies the moonlet is protruding about 660 feet above the ring plane. If the moonlet is orbiting in the same plane as the ring material surrounding it, which is likely, it must be about 1,300 feet across. All photos credit: NASA / Cassini Mission

Jagged looking shadows stretch away from vertical structures of ring material created by the gravitational pull of the moon Daphnis. Daphnis, 5 miles across, is a bright dot casting a thin shadow to the left and above the center of the image. How cool is this photo!

A vertically extended structure or object in Saturn's F ring (bright, narrow band at far left) casts a shadow long enough to reach the A ring (right) in this Cassini image taken just days before planet's August 2009 equinox. The structure can be seen as a bulge within the bright core of the F ring on the left of the image.

And now, just for your enjoyment, take a look at this stunning (and large) map of every object in the solar sytem larger than 200 miles across. There are many of them!

Posted by: rking@duluthnews.com on 8/7/2009 at 9:07 PM | Comments (0) | Permalink

Hot news from cold space

Lively hour for the Perseids?

Meteor watchers are getting more excited than usual for next week's peak of the annual Perseid meteor shower. Almost anyone who's been out on an August night has seen a Perseid streak by at one time or another. The meteors are bits of dust left behind by Comet Swift-Tuttle. Each year our planet intersects the orbit of the comet, and the crumbs vaporize in our atmosphere as meteors.

While the shower reaches maximum on August 11-12, skywatchers may be in for a bumper crop of meteors between the hours of 3 and 4 a.m. Central time next Wednesday. That's when Earth is expected to pass through a thicker-than-normal filament of comet dust. Scientists are forecasting the activity to double during that time to something like 100 meteors per hour. We'll have much more on the Perseid shower early next week so stop by again for updates.

Metal meteorite discovered on Mars

This hunk of rock is actually a nickel-iron meteorite similar to the one that created Meteor Crater in Arizona. It was discovered on Mars by the Opportunity Rover and measures about two feet across. Credit: NASA/JPL-Caltech/Cornell University

The Opportunity Rover pulled up for a closer look and analysis of the purported meteorite it came across while en route across the Martian plains of Sinus Meridiani. Named "Block Island", composition measurements confirm the rock contains iron-nickel, a key component of meteorites. Take a look at that dimpled surface too. The hollows were likely caused by softer material melted away by friction with the thin Martian air as it plunged to the surface. We see similar "thumbprints" on meteorites found on Earth.

 

A fragment of the Sikhote-Alin meteorite that fell over Russia in February 1947. It has a similar texture to the Block Island meteorite on Mars. Credit: H. Raab

Kepler spots an exoplanet's atmosphere

This artist's view shows a "hot Jupiter" in close orbit about its host star.
NASA's Kepler observatory recently determined the size, temperature and other details about the planet called HAT-P-7 around a star 1000 light years away. Credit: NASA

Yesterday NASA announced that the Kepler spacecraft, which is watching a huge sample of stars in the space between Deneb and Vega at the top of the Summer Triangle, detected the atmosphere and changing phases of a planet orbiting a distant star. Kepler's mission is to find and characterize new exoplanets (planets around stars other than the sun) by watching them pass in front of the stars they orbit. By studying how a star's light changes during a pass, called a transit, scientists can ferret out particulars about the planet. 

Kepler's finely-tuned instruments have the ability to detect Earth-sized planets, the Holy Grail of astronomers seeking other worlds with the potential for life. This particular planet, HAT-P-7, is 26 times closer to its star than Earth to the sun and completes an orbit in just 2.2 days. It's larger than Jupiter and has an atmosphere with a daytime temperature of 4,310 degrees. Ouch! Many exoplanets like this one have been found and they're nicknamed "hot Jupiters". Not exactly the place you'd expect life, but give Kepler time. It's mission has only begun. For more on Kepler, see this earlier blog.

Posted by: rking@duluthnews.com on 8/7/2009 at 10:31 AM | Comments (0) | Permalink

Madness by moonlight

 
This sweet photo of the Duluth's Lakewalk and Canal Park area was taken Tuesday night under the nearly full moon by Dan Hass of Duluth. The Aerial Lift Bridge is aglow just right of center. Details: Canon PowerShot SX1 camera, f/2.8 at 15 seconds with an ISO of 80. Credit: Dan Hass

OK, I may have to change my mind about the full moon making people go crazy. Last night my neighbors had yet another party that went on till dawn. The throb of bass from the music filled the neighborhood like the sound track to one of those aliens-destroy-humanity movies. At the same time, the full moon shown down on the lawn with great radiance, its light steady, peaceful. You can see the two again tonight just a bit closer together than last. Look to the southeast around 10 o'clock to quench your celestial thirst.

Another fine moonlight composition, this one taken last night at the Lester River in Duluth. Jupiter is just to the left of the moon. Credit: Dan Hass

The moon and Jupiter around 10 p.m. tonight (Aug. 6). Created with Stellarium.

I also took the scope out briefly and pointed it at Jupiter, but the air turbulence was so strong the planet's image boiled like oatmeal in a pot. I should have known. The stars were twinkling madly, an almost certain sign that busy air currents were messing up the delicate threads of starlight. Twinkling or scintillation is absent on the moon because it has no appreciable atmosphere. While sparkling stars are attractive to the naked eye, air currents mess up magnified images in the telescope. And the lower in the sky you point the scope, the denser the air and the worse the image.

Light from a star travels a long way through space until it encounters our atmosphere. Shifting air currents and variable temperatures batter the light about causing the star to twinkle. The lower in the sky, the more pronounced the twinkling. Planets twinkle far less than stars because they have sizeable disks which are less affected by turbulence. Illlustration: Bob King

So it was with Jupiter. And if you're ever out and see the same mushiness, don't blame your scope straight off. It's likely the air. That's why amateur astromers observe on as many nights as possible in order to secure a few with steady air or what we call "good seeing". Then the views of planets are crisp and real with nothing in the way. Time and sleep become secondary concerns as you stand absolutely absorbed by what you see.

Posted by: rking@duluthnews.com on 8/6/2009 at 10:42 AM | Comments (1) | Permalink

Thoughts on a distant sun

Sunshine lights the scene at Holy Rosary School in Duluth Wednesday morning. The sun is 93 million miles away and converts hydrogen in its core to helium (nuclear fusion), creating energy in the process. Photo: Bob King

The sun commands a powerful presence in our lives. Burning hydrogen as fuel, its radiant orb provides the necessary heat to keep our planet warm, alive and thriving. We're so close to it, relatively speaking, that the sun is much too bright and dangerous to look at directly. Even though we know that all those other tiny dots in the nighttime sky are other suns, we don't have an intuitive feel for their true brilliance and fierce heat. Our sun stands apart and our lives depend upon its reliability.

An artist's view of Pluto's icy surface and its moon Charon. The sun, at upper right, would appear as a brilliant laser-like point of light. Credit: ESO/L. Calcada

That got me to thinking how far you'd have to travel away from the solar system to see the sun's stature reduced to that of a nighttime star. At first, you might think that buzzing out to the dwarf planet Pluto in the chilly outer burbs would do the trick. At around three billion miles away, the sun would be reduced to a brilliant point of light 1000 times brighter than the full moon. Ever accidentally look into a laser beam -- that's what the sun would look like. That's plenty bright to illuminate Pluto's bitter cold landscape of methane ice. While you wouldn't be able to resolve the sun's disk with your naked eye, it would appear about as big as Jupiter's disk does through a small telescope here on Earth. You'd just make out the shape at about 10x magnification.

The sun is similar in size to the two brightest stars in the Alpha Centauri triple star system. Credit: David Benbennick

While Pluto hints at what's to come, we'll need to travel further to lose the sun among the starry multitude. Let's stop at Alpha Centauri, a triple star 4 1/2 light years away and the nearest star beyond the sun. We're going to assume we can stand on an Earthlike planet there and look up into a clear night sky. When we do, we would notice a bright, new star just to the left of the W of Cassiopeia. A keen-eyed observer might even discern its pale-yellow tint. That's good old sol!

The sun appears in Cassiopeia in the sky above an imagined planet orbiting Alpha Centauri. Our star would shine a bit fainter (half a magnitude) than Vega, the brightest star in the Summer Triangle. Vega is almost directly overhead at nightfall in early August. Created with Stellarium.

The sun from Alpha Centauri would be almost as bright as Vega in the Summer Triangle and easily make the Alpha Centaurians "Top 50 brightest stars" in the sky list. How about the view through a telescope? Just a point of unresolved light like all the others. No planets would be visible either; all would be too close to the sun and hopelessly lost in its glare. If we continued our journey to Sirius, which is 8.7 light years distant and the brightest star in our earthly sky, the sun would only be as bright as the stars of the Big Dipper. According to the Inverse Square Law, every time you double the distance, a star's brightness fades by four times.

Writing this is starting to give me the chills, so let's pull back from deep space and once again enjoy the pleasure of the sun's company on this fine August day.

Posted by: rking@duluthnews.com on 8/5/2009 at 11:29 AM | Comments (0) | Permalink

Gathering time for lunatics

A sheet of cirrocumulus clouds produces a striking partial corona of color around last night's gibbous moon. Light from the moon is diffracted by the tiny water droplets composing the cloud, creating a disk of blue and ruddy orange. Details: 100mm lens at f/5, 3-second exposure at ISO 200. Photo: Bob King 

The moon is nearly full tonight and not very far from Jupiter. Tomorrow night it will be at full phase and even closer to the planet. August's full moon is the Full Sturgeon Moon, named by tribes of the Great Lakes for the best time to fish for sturgeon.The map shows the sky looking southeast about 10:15 p.m. Created with Stellarium.

Tonight looks ideal for sauntering about in the moonlight. To the casual glance, the moon will look full, but true full phase won't occur until tomorrow night when the moon joins Jupiter in the southeastern sky. It's no coincidence the moon is near the planet. You'll recall that a full moon is defined as the lunar phase that's directly opposite the sun. The moon rises near sunset, its face fully illuminated by the sun's light. At full phase, the moon is said to be at opposition to the sun. Jupiter is nearly at opposition too which is why they're close pals tomorrow night. To keep abreast of the moon's phase, click on this website for a handy calendar.

The Big Dipper and the seven bright stars that compose it. I also added fainter Alcor, which is a companion star to Mizar. After a season-long stint near the top of the sky, the Dipper is easing back down toward the northern horizon. Photo: Bob King

As the nights are getting longer, have you noticed the Big Dipper sinking lower in the northwest? The Dipper is and has been one of the most easily-recognized star patterns since antiquity. Seven similarly-bright stars are arranged in a pattern that many cultures -- from European to Native American -- have long viewed as a bear. It's a bit unclear exactly why, since the shape doesn't obviously look bearlike unless you like your bears with very long tails. Only when you take into account all the faint stars around the Dipper does it begin to assume a more bear-like form.

A farmer plows his fields using the traditional horse-drawn plow method. Credit: Ralf Roletschek

Since the pattern is so distinctive, it should come as no surprise that the Big Dipper has also been known by other names, some of which fit the picture better. In Great Britain, it's called the Plough (Plow). Three stars form the traditional horse-drawn plow's handle while the blade and wheels are the bowl. In the Middle Ages in Britain, the Dipper was also called Charles Wain or Charles' cart, a name whose origin goes all the way back to King Charles the I or Charlemagne, King of the Franks.

The Dutch call it the Saucepan, in Hindu it's referred to as the Seven Great Sages, African-Americans in the days of slavery called it the Drinking Gourd, the Lapps of Finland saw the stars as reindeer, some Arabic peoples envisioned a funeral train with the handle stars as mourners behind the coffin (bowl) and several Native American tribes saw the handle as hunters tracking the bear (bowl).

Going back further, the ancient Egyptians looked up and saw a Bull's Thigh while the Greeks called it Arctos the bear. From ancient China comes one of the scarier names any constellation has ever received -- Tseih Sing or the Government.

The next clear night, take a look yourself and see if the Big Dipper reminds you of anything else. What would you name this most famous asterism if you could? And while you're out, why not practice your Arabic by learning the names of all seven stars? Here's a short guide to their pronounciations:

* Alkaid (al-KADE)
* Mizar (MY-zar) and Alcor, its companion (AL-kor)
* Alioth (AL-ee-oth)
* Megrez (meg-REZ)
* Phecda (FEK-duh)
* Merak (MARE-ak)
* Dubhe (DUB-ee)

(Information on the Dipper's many guises comes from a book by Richard Hinkley Allen titled Star Names: Their Lore and Meaning. If you'd like to dig more deeply into the constellation lore, the entire book is available online. Just click the title link.) 

Posted by: rking@duluthnews.com on 8/3/2009 at 10:33 PM | Comments (2) | Permalink

Batter up!

The Great Square of Pegasus comes up in the east in early August around 10:30 p.m. Its sides measure about one outstretched fist across. The square is part of the larger figure of Pegasus the Winged Horse which we'll look at in more depth next month. Created with Stellarium.

It's midsummer and we're deep in the pocket of baseball season. As if in harmonic convergence, a grand baseball diamond is nudging its way into the evening sky. If you face east around 10:30 p.m. and look three outstretched fists below and to the right of the W of Cassiopeia, you'll spot the Great Square of Pegasus. Come October and November, when Pegasus is due south in the early evening, it looks as square as its name, but in August the figure stands on one corner and looks much more like a diamond.

Moderately bright stars mark all four bases; the only thing missing is the pitcher's mound. Truth be told, the leftmost star of Pegasus officially belongs to neighboring Andromeda, but the four-cornered asterism is so beloved, few skywatchers associate it with that constellation.

Stars that appear in the east during summer nights are transitional to fall. That big empty diamond not only brings baseball to mind but also bare trees and falling temperatures. For now, Pegasus is biding his time, but as the Earth moves along its orbit, causing the constellations to drift westward with the seasons, the empty square will take on new meaning.

The Chandra X-ray observatory photographs energetic events in the universe like exploding stars, matter streaming down black holes and supernovas. It's named after famous Indian astrophysicist Subrahmanyan Chandrasekhar Credit: NASA

I got an e-mail the other day from a reader who had a question about a fascinating discovery by the Chandra X-ray observatory this past spring. Chandra (SHAHN-druh) is a special telescope that orbits the Earth and "sees" the sky in the light of X-rays, a very energetic form of radiation that's shot out into space by high-energy objects like exploding stars. Since X-rays slam right into glass without reflecting back, Chandra uses a set of four nested cylindrical mirrors that look something like glass barrels. Incoming X-rays glance or richochet off the sides of the mirrors before coming to a focus below.

The Hand Pulsar glows eerily in the southern constellation of Circinus the Drafting Compass. Within the bright spot is the rapidly-spinning core that remains after a star explodes as a supernova. The pulsar is spewing particles that form the white clouds. Energy transferred from the clouds to another nearby gas cloud causes it to glow orange. Image courtesy NASA/CXC/CfA/P. Slane et al.

One of Chandra's discoveries was a large nebula or gas cloud in the form of a human hand some 17,000 light years away. At its center is a 12-mile-diameter star called a pulsar that's spinning seven times per second. The star's rapid rotation combined with the energetic wind of particles it spews have created a remarkable nebula 150 light years across.

The nebula's shape, just like the stars that form the Great Square, is a chance occurence. Thanks to our penchant for seeing patterns in so many things around us, we readily associate a fair degress of randomness with particular shapes. No doubt it simplifies sharing information as well as helping us find our way back again.

Posted by: rking@duluthnews.com on 8/3/2009 at 10:17 AM | Comments (0) | Permalink

Jupiter-spot news plus the Toolkit bids adieu

Jupiter's dark impact spot, seen near the top of the planet, continues to stretch and lengthen. Just recently it developed an additional hook feature to the left. The shape reminds me of a flock of geese. These two photos were taken early on August 1 about an hour apart. Credit: Paulo Casquinha of Palmela, Portugal

I almost set the alarm the past two mornings to check up on the Jupiter's black spot but after sleeping on the ground for a couple nights while camping, I needed real rest. Fortunately others were more industrious. The photos by Paulo Casquinha show how the spot has continued to expand and morph in shape as it gets pulled by Jupiter's powerful winds. The dark color is caused by blackened debris that rained down on the atmosphere after the flash of impact.

The good news is that as the spot grows, it becomes easier to see in smaller telescopes. I want to encourage you to get out and look while you can, because the Jupiter's scar will eventually be absorbed into the planet's atmosphere and disappear. No one knows when the next impact might occur. It could be tomorrow or a thousand years from now.

Here are some times when the spot will be easiest to see. If you balk at how late they are, I completely understand. But keep this in mind. Each night Jupiter rises four minutes earlier due to Earth's orbital motion around the sun. Eventually the planet will be up at much more convenient time for early evening viewing. Let's hope the spot sticks around for that to happen.

Look toward the far southern end of the planet to find the impact spot.
* Tonight around 11-11:30 p.m. Central time (Jupiter will be low in the sky however)
* Tues. morning Aug. 4 from 3:30-4:30 p.m.
* Tues night Aug. 4-5 from 11:30-1 a.m.
* Fri. morning Aug. 7 from 1-2:30 a.m.
* Sun. morning Aug. 9 from 3-4:30 a.m.

In this image from NASA TV, a tool kit bag, center, as seen through the helmet camera of astronaut Heidemarie Stefanyshyn-Piper, floats away from the International Space Station. She accidentally let go of the bag when a grease gun inside erupted. Credit: NASA 

Do you remember the lost Toolkit, adrift in Earth orbit since it slipped out of the hand of astronaut Heidemarie Stefanyshyn-Piper when she was working outside the International Space Station last November? The kit is about the size of a suitcase and visible as a faint, naked-eye or binocular "satellite". That's about to change. Over time, the Toolkit's orbit has been gradually dropping closer to Earth or "decaying". It's now predicted to burn up in a brilliant fireball somewhere over the Pacific Ocean tomorrow morning (Aug. 3) around 8 a.m. Central time.

It won't be visible tonight from northern Minnesota/Wisconsin but other locations might get one last chance before it becomes toast. To find out, go to the Heavens Above website, log in, select your city and click on the ISS Toolbag link.  

Here are a couple photos from a recent trip I made to the Boundary Waters canoe country in northeastern Minnesota. Among the highlights was a moonlight canoe paddle on Weird Lake (yes, that's the real name) Thursday night. Gliding through the quiet darkness above the liquid reflection of the moon was deeply satisfying. From time to time, we need to see what the world looked like before our arrival.

A time exposure of Weird Lake by the light of the moon. I briefly pointed my flashlight at the canoe during the exposure. The star Arcturus is reflected in the water to the left of the bow. Photo: Bob King

My friend Rick (right) and I on Weird Lake just before heading back home. Photo: Rick Klawitter

Posted by: rking@duluthnews.com on 8/2/2009 at 10:30 AM | Comments (0) | Permalink

Retro is in with Big Jupes

The gibbous moon in Sagittarius and brilliant Jupiter light up the sky tonight in this view looking toward the S-SE around 10:30 p.m. tonight. Maps created with Stellarium.

Earth's rotation causes all the planets and stars to rise in the east and set in the west, but the stars keep their places in the sky while the planets slowly drift to the east through the zodiac constellations over the months and years. That's why they're called planets, from the ancient Greek word for "wanderers". The eastward movement is a consequence of the planets' orbital motion around the sun as seen from our perspective here on Earth.

If you look at our map of Jupiter over the next two months, you'll notice something peculiar. Jupiter isn't moving to the east at all. It's picked up stakes and now headed west. What's going on here?

This map shows Jupiter's retrograde motion in Capricornus the Sea Goat, a fainter zodiac constellation, starting tonight (Aug. 1) through September. Thanks to several nearby stars -- Delta, Gamma and Iota -- it will be easy to watch the planet's weekly march to the west.

All the outer planets -- Mars, Jupiter, Uranus and Neptune -- are further from the sun than we are and so move more slowly in their orbits. As our planet catches up and overtakes an outer planet, it appears to slow down in the sky, stop and then move westward for a time. Once we've swung around it, the planet slows down again and resumes its normal eastward motion. This temporary "backwards" movement is called retrograde motion. The Mars animation below illustrates it very nicely.

As Jupiter retrogrades this month and next, it happens to pass close by several stars in Capricornus so it's westward movement will be obvious is less than a week. If you live near a downtown, the stars might be hard to see with your eye but binoculars will show them easily.

To watch this animation, just click on the photo to take
you to the website, then click the start button. Credit:
University of Nebraska-Lincoln

It's fun to watch the planet move in relation to the stationary stars. As you do, keep in mind you're watching a race, one where the speedier Earth is overtaking the mightiest of planets. As summer gives way to fall, Jupiter will slow down and linger for weeks near the star Iota, then resume its normal or direct motion to the east in late October. By next summer, Jupiter's orbital motion will carry it all the way to Aquarius, the next zodiac constellation east of Capricornus.

Here's a view of an outer planet's "backwards" motion
broken down into five steps. Credit: Brian Brondel, with
my own annotations.

Posted by: rking@duluthnews.com on 8/1/2009 at 9:30 AM | Comments (2) | Permalink

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