OMG ... the sun

A pussy willow bud is coated with hundreds of tiny water droplets this morning after an overnight foggy mist. Photo: Bob King

The sun returned this morning after a week's absence. I almost couldn't believe it. How wonderful to feel the heat on my back and hear the robins again. When I saw clusters of water droplets on the pussy willows, star clusters came to mind. Since we spent several days last week exploring the different types it only seemed natural to wrap up the star cluster theme with a watery variety close to home.

The International Space Station (ISS) will continue making passes over the region during convenient viewing hours throughout the coming week. Here are the times for Duluth and region when you can see it. For times for your city, click HERE and type in your zip code. A typical pass lasts about five minutes as the ISS travels from west to east.

* Tonight starting at 7:51 p.m. with a bright pass across the northern sky
* Monday March 15 at 8:16 p.m. Very bright pass across the northern sky. Close to Polaris the North Star at 8:19.
* Tuesday March 16 at 8:41 p.m. Brilliant pass. The ISS rises in the west and makes a beeline to nearly the top of the sky, fading out just to the left of Mars.
* Wednesday March 17 at 7:30 p.m. Nice bright pass across the north. Nearly touches Polaris at 7:33 p.m. 2nd pass across the southwest at 9:06 p.m.
* Thursday March 18 at 7:55 p.m. Brilliant pass. Watch for it close to Mars just before 8 p.m.
* Friday March 19 at 8:20 p.m. low pass from southwest to southeast
* Saturday March 20 at 8:46 p.m. Very low pass from southwest to south

The ISS back in the early days. The mated Russian-built Zarya (left) and U.S.-built Unity modules are backdropped against the blackness of space and Earth's horizon shortly after leaving Endeavour's cargo bay. The photo was taken on Dec. 13, 1998. Credit: NASA

The space station has certainly grown since construction began in 1998. It started as just two modules -- the U.S.-built Unity and Russian Zarya -- and has since expanded to 11 pressurized modules and will eventually weigh 450 tons. Once completed in 2011, the ISS will be 356 feet long by 239 feet across, almost exactly the same size as a football field including the end zones (360 x 220 feet). Three more modules remain to be launched. The ISS completes 15.7 orbits per day traveling at an average speed of 17,227 miles per hour. It's the most diverse laboratory and viewing platform ever constructed. Astronauts there have conducted experiments on the long-term exposure to a near-weightless environment on everything from monarch butterflies to ourselves. While the space station has its critics, just about any branch of science you can think of has been studied from an outer space perspective on the ISS. And let's be honest, it's just fun to watch. For a sampling of some of the station's benefits, please click HERE.

My, how we've grown! The mostly completed space station orbits above the ocean in this photo taken on February 19. Credit: NASA

A flame looks different in the "zero g" environment of the space station than it does on Earth. On Earth, a candle burns with a tall, yellow flame. In space, a smaller, blue flame burns on the center of the wick. As hot gases from a flame rise, they create air currents that bring fresh air to the fire. This buoyancy is what makes a flame long and pointed here on Earth. In low gravity situations, there is no buoyancy from flames. Credit: NASA

Posted by: rking@duluthnews.com on 3/14/2010 at 10:03 AM | Comments (0) | Permalink

Wrinkle in time

The fastidious will walk around their homes tonight setting all the clocks ahead one hour in anticipation of the changeover to daylight saving time Sunday morning. Most of us won't bother until well after we get up on Sunday. My clock meddling begins with the microwave and ends several days later with the LED on the car's dashboard. How many clocks do you change in your house? Our tally comes to seven. I wonder ... do we need that many clocks?

This map shows the sky as you face east tonight at 8. Arcturus will have just risen and Saturn will be up a little higher. Maps created with Stellarium

Since we "spring ahead" or advance an hour that means the sun will set an hour later Sunday. We welcome the evening light. It makes driving home from work easier and coaxes us outside after dinner. Tonight the sun sets at 6:11 p.m. in Duluth; tomorrow it sets at 7:13 p.m. Add in a little less than two hours for twilight, and the sky won't be truly dark Sunday until around 9 o'clock.

Now we're looking the same direction at the same time Sunday night. Because of the changeover to daylight time, Arcturus has yet to rise and Saturn scrapes the eastern horizon.

The changeover to daylight time also causes a one-hour shift in the stars' positions. If you look toward the east around 8 p.m. tonight and follow the arc of the handle of the Big Dipper you'll run into the brilliant star Arcturus. Three fists to the right of Arcturus and a little higher in the sky is the planet Saturn. Go our tomorrow night at the same time and Arcturus won't even be up yet while Saturn will have just risen. Not to mention that the sky will still be aglow with twilight. To see Saturn and Arcturus like you will tonight, you'll have to wait until 9 p.m. on Sunday -- one hour later than normal.

In the western sky, daylight time has the opposite effect. Stars that tonight are low in the sky at 8 p.m. will be an hour's worth of time higher up on Sunday. While advancing our clocks an hour ahead, we've artificially shifted the entire night sky an hour's worth of time to the east. In fall, we "fall back" and shift the sky an hour in the western direction.

Although most of us don't like losing that hour of sleep from changing our clocks there is one advantage. Sunrise is an hour later so the sky stays dark in the morning making it easier to stay asleep and finish off those pleasant dreams.


Here's a unique video of multiple comets diving into the sun made over the past three days -- ice meets fire! The bright "star" with the bar through it is Mercury while the sun is hidden behind a disk to block glare.

Yesterday a comet -- or series of comets really -- brightened up briefly before plunging headlong into the sun. The video shows that most of the comets were tiny but one was larger and put on a good show before it dissipated. All of them were most likely fragments of a single larger comet that broke up more than 2000 years ago. The photos used in the video were taken by the coronagraph aboard the Solar Heliospheric Observatory (SOHO) which can observe the sun 24 hours a day.

Posted by: rking@duluthnews.com on 3/13/2010 at 12:19 PM | Comments (0) | Permalink

In praise of bicuspids

The very thin crescent moon will be visible low in the eastern sky about 40 minutes before sunrise tomorrow morning. The map shows the approximate position of the sun, which is below the horizon at the time, to help you gauge the separation between it and the moon. Created with Stellarium

The moon is headed toward New Moon phase and a fine conjunction with Venus early next week but before it does those with a wide open view to the east can spot the skinny waning crescent tomorrow morning before sunrise. If you like the look of a crescent moon you may want to explore other moon crescents elsewhere in the solar system. Venus and Mercury sadly have no moons but the rest of the planets all come with company. Here are the current moon totals:

* Earth: 1
* Mars: 2
* Jupiter: 63
* Saturn: 62
* Uranus: 27
* Neptune: 13
* Pluto: 3

Add 'em all up and you get 171. Thanks to spacecraft flybys and orbiters we've been able to see many of them up close and showing phases just like our own moon. The key to seeing moons or even planets as crescents is to get around their backsides so they're nearly lined up with the sun. From this perspective we see only their edge or rim illuminated by the sun, and an "edge" on a spherical body is naturally a crescent of light. Spacecraft can do this for many different solar system bodies because we send them to faraway places like the backside of Jupiter or behind Saturn's moon Titan. You and I meanwhile are literally stuck on Earth -- with the exception of Mercury and Venus.

Using Venus as an example, we see how planets and moons look like crescents (C and D) when they're nearly in line with Earth and the sun. From our perspective behind Venus we see mostly the planet's backside with a thin sunlit edge. Technically, a spherical planet or moon will look like a crescent if the angle between it, the sun and Earth is greater than zero but less than 90 degrees. Illustration: Bob King

We see Mercury and Venus as crescents during part of their revolutionary cycles because Earth is in the next orbit out. When the two planets get approximately between us and the sun we see their backsides. If you've never seen them in this phase through a telescope, you'd be surprised how much they mimic the lunar crescent. When the planet-sun-Earth angle is exactly 90 degrees, the planet looks half lit as in B and E above. Less than 90 and it starts to assume a crescent phase, fat at first and then thinning as the angle between the three narrows.

How about double the fun? In this sequence of images taken by the Cassini spacecraft, Saturn's moon Enceladus (foreground) passes in front of larger Rhea. Credit: NASA/JPL/Space Science Institute

There's beauty in that hammock-like arc contrasting with the sharpness of the cusps. For your pleasure, I've selected several alien crescents for your perusal. All these images come to you courtesy of our robotic emissaries who've gone the distance and turned around to look back from perspectives not available to humans ... yet.

This photo of Jupiter's moon Io was taken on March 2, 2007 by the New Horizons spacecraft that flew by Jupiter en route to Pluto. Backlighting from sunlight brought three active volcanic plumes into clear view including the 190-mile high plume from the Tvashtar volcano at top. It appears blue because of the scattering of light by tiny dust particles ejected by the volcano, similar to the blue appearance of smoke. You can see the red glow of lava at the plume's source. The right side of Io is faintly lit by sunlight reflecting off Jupiter. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

The planet Neptune and largest moon Triton were photographed by the Voyager 2 spacecraft during its flyby in 1989. Credit: NASA

Saturn as seen by Cassini in 2006. The weird shadows are cast by the rings which extend down toward the bottom of the picture. Credit: NASA/JPL/Space Science Institute

OK, so it's not exactly a crescent but you get the idea. Saturn's 20-mile diameter moon Helene is irregular in shape so its "crescent" is too. Helene's backside is dimly illuminated by sunlight reflecting off Saturn. The picture was taken during Cassini's close flyby on March 3. Credit: NASA/JPL/Space Science Institute

Posted by: rking@duluthnews.com on 3/11/2010 at 5:57 PM | Comments (3) | Permalink

The star cluster that cheated death

Cancer is located in that "empty space" between Leo and Gemini. In addition to Mars, Cancer features two other gems for the naked eye and binoculars -- the open star clusters M44 and M67. This map shows the sky as you look high in the south around 9 o'clock in mid-March. Created with Stellarium

Dim Cancer the Crab would probably be lost in obscurity if not for the fact that the sun and all the planets routinely cross its borders as they cycle around the sky. Cancer is one of the 12 zodiac constellations featured in daily horoscopes but often overlooked by first-time star gazers because none of its stars is brighter than 4th magnitude. The crab hides in his shell between the brighter, more familiar Gemini the Twins and Leo the Lion.

Let's take a second look at this constellation and see if we can't find a few good reasons to seek it out the next clear night. We begin with Mars, which has resided in Cancer since early winter. You couldn't find a better guide to direct you to the constellation's faint upside-down "Y" figure. Mars is midway between its bright neighbor Pollux in Gemini and the center of the Y. Not far from this point is the Beehive star cluster, also known as M44, that looks like a mysterious puff of light on dark, moonless nights.

The Beehive (at right) is an open cluster comprised of hundreds of stars at a distance of 577 light years. Its age and direction of motion within the galaxy are the same as that of the Hyades Cluster in Taurus implying that the two likely originated in the same cloud of galactic dust and gas 700 to 800 million years ago. Like individuals born in the same town but now leading lives on opposite coasts, the two have gone their separate ways. Binoculars will resolve M44's cloudy glow very well showing several dozen stars where the naked eye fails to see even one.

Once you're comfortable with navigating to the Beehive, drop down a little more than one binocular field of view below the cluster to Cancer's other claim to fame, the ancient open cluster M67. While I've seen M67 with the naked eye as a tiny spot of light under very dark skies, it's much nicer in binoculars. In my 8x40s I see a smudgy glow that's elongated in a north-south direction and peppered with several faint stars.

This is what M67 looks like in a telescope. Even small scopes can resolve this rich cluster into many stars. Several red giant stars are visible within its borders. Credit: Jim Misti

What makes M67 even more interesting to astronomers is its age of four billion years. Yesterday we examined the differences between open and globular clusters and age was a big factor. Typical open clusters have lives measured in the millions of years, while globulars hang around for double-digit billions. M67 is one of the oldest open clusters known and the oldest by far in Charles Messier's catalog of "M" objects. Since it's nearly the same age as our own solar system (4.5 billion years), astronomers find it an excellent place to study sunlike stars. The cluster has more than 100. Interestingly, a number of them exhibit much more magnetic activity than our sun does even when at its peak. One group of astronomers has determined this is because the sunlike stars in M67 are rotating more rapidly than our sun. Rapid rotation leads to more intense magnetic fields on stars' surfaces which increases the number and intensity of flares and associated activity.

The big question is how did M67 keep itself together for so long? Unlike so many open clusters it's not located in the plane of the galaxy but rather hovers some 1500 light years above it. Away from the fray and beyond much of the gravitational interaction with other stars in the disk, the M67's found a "quiet place" where it can wax to old age in relative peace. There may be other factors involved too, but its location clearly contributes to its longevity.

The coelacanth, now in the Natural History Museum in Vienna, Austria, was caught in the Comoro Islands in 1974. Credit: Alberto Fernandez Fernandez

Ever hear of the coelacanth fish? This very successful animal was long thought to have gone extinct at the end of the Cretaceous period 65 million years ago, but in 1938 a live coelacanth was discovered off the east coast of South Africa. Since then others have been found in various locales including Kenya and Tanzania. Like the coelacanth, M67 is a living fossil still thrumming about in the galactic deeps.

(Photo of M44 above: Bob King)

Posted by: rking@duluthnews.com on 3/11/2010 at 10:17 AM | Comments (0) | Permalink

Disco ball infernos

Phobos orbits above the hazy Martian atmosphere in this image taken by the High-Resolution Stereo Camera on board Mars Express on January 22, 2007. Credit: ESA/ DLR/ FU Berlin (G. Neukum)

While waiting for the latest photos from the recent close flyby of Mars' moon Phobos by the Mars Express I dug up a photo of the moon taken a couple years earlier. It's so "out there" I thought you'd enjoy seeing it. If Phobos looks small and boulderish, it's no surprise -- the little guy's only 13 miles in diameter. That's too small for the moon to crunch itself into a sphere.

Earth's moon orbits at an average distance of 239,000 miles. In this photo taken Monday, the moon is setting into snow blowing from 13,658 ft. Mt.Tom in the Sierra Nevada of California. Unlike Phobos, our moon is slowly creeping away from the Earth at the rate of 1.5 inches per year ... but that's a story for another blog :) Credit: Andrew Kirk

Phobos orbits 3,728 miles above the planet's surface or more than 60 times closer than our moon does to Earth. Mars' gravitational dominance over Phobos causes its orbit to shrink by 66 feet per century. In about 10 million years Phobos will spiral to within 2,249 miles of the surface at which point the tidal forces exerted by Mars will disrupt and shatter the moon. Remnants of Phobos will form a temporary ring around the planet. A tidal force is the difference between the strength of Mars' gravitational attraction on the front side versus the back side of Phobos. At a point called the Roche Limit, tidal forces are strong enough to overcome the smaller body's structural integrity causing it to disintegrate into fragments.

You can keep up with Phobos news by visiting the Mars Express blog.

The brightest globular cluster in the sky is Omega Centauri. It's visible from the far southern U.S. in the constellation Centaurus and contains an estimated 10 million stars. Credit: ESO/EIS

I don't know about you but we've been socked in with clouds here in the Duluth area for the past few days. The stars clusters we looked at yesterday will be well-placed in the evening sky for at least a few more weeks so there's plenty of time for viewing them. M50 and NGC 2244 are known as galactic or open clusters because they reside in our galaxy's flat disk and they're open and "airy" compared to the dense balls of stars called globular clusters. Globular comes from globulus, the Latin word for "globe". Globulars (GLOB-you-lars) resemble disco balls dangling in a vast spherical halo about the center of the Milky Way galaxy.

This is a photo of the Milky Way galaxy made by the COBE satellite in the light of infrared. Infrared penetrates the galaxy's dust clouds to show its true shape. The yellow dots I've added represent globular clusters centered on our galaxy's core or bulge. The sun and planets reside in the disk about halfway between the core and edge. Credit: NASA

Open clusters have anywhere from a couple handfuls to 10,000 stars while globulars start at 10,000 and range up to a several million stars. Beside their obvious differences in appearance and star count, each has evolved in entirely different ways. Globulars are very ancient -- 10 billion years and older -- and their origins go back to the time of the Milky Way galaxy's formation. They first appeared during a long-ago era of vigorous star formation when the massive gas cloud that was to become our galaxy collapsed under the force of gravity to create the globulars as well as the billions of stars that reside in the core and halo. Because the globulars are distributed in a sphere centered on the galaxy's core, it's likely they formed very early on and trace the shape of the original birth cloud. As the cloud spun and contracted, it gradually collapsed into a thin disk to resemble the structure of today's galaxy: a pancake-like disk with a central hub surrounded by a halo of globular clusters.

You can really see the difference between the two cluster types in these photos. To summarize: open clusters are young, reside in the galaxy's disk, have relatively few stars and break apart over relatively short times. Globulars are ancient, reside in the galaxy's halo, have far more stars and hang onto their members for a much longer time. About 1100 open clusters and 150 globulars have been discovered in the Milky Way galaxy. Photos: Bob King (left) and NASA.

Open clusters formed later from the gas and dust processed by earlier generations of stars born within the disk. If globulars are the galaxy's immortals, open clusters like M50 are the young whippersnappers. Both types of star clusters are held together by their own gravity, but the densely-packed globulars hold their many stars more tightly compared to the loose open clusters. As open clusters revolve about the galaxy's core, members stray away and the cluster dwindles. In addition to gravitational interference from random dust clouds and passing stars, each star within an open cluster also has its own individual motion. Like a wild colt, a cluster member can bolt into space on its own leaving its cozy home behind.

Other galaxies have their own assortment of clusters. In this photo of the giant galaxy M87 in Virgo, the tiny star-like points you see are just some of its more than 10,000 globulars. The blue jet next to the galaxy's core is material shot out by a supermassive black hole in its center. Credit: Hubble Space Telescope/NASA/ESA

Without enough mass to hold themselves together against the push and pull of intergalactic gas clouds or their own individual motions, many open clusters dissipate in a few tens of millions of years. It's likely that a good number of the individual stars we see in the nighttime sky were once members of star clusters. New open clusters are forming all the time in nebulas like the Rosette (see yesterday's blog) because there's still plenty of recycled gas and dust in the galaxy's disk. Globulars formed a long time ago and used up the material available in the halo back then. No new globulars are seen to form in the Milky Way today.

There are open clusters that do have what it takes to hang together for much longer. Tomorrow we'll visit with the constellation of Cancer the Crab and meet one of the few survivors.

Posted by: rking@duluthnews.com on 3/9/2010 at 8:42 PM | Comments (0) | Permalink