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

Step into the triangle of delights

The Winter Triangle lies to the east of Orion's three belt stars and high in the south-southwestern sky around 8 o'clock. You'll find the Rosette Nebula not quite one outstretched fist to the left (east) of Betelgeuse. M50 is about the same distance above brilliant Sirius. Photo: Bob King

Several days ago we looked at the peculiar exploding star V838 Mon in Monoceros the Unicorn. You'll recall that this dim constellation is mostly within the confines of the bright Winter Triangle. The Milky Way slices through the region and offers up many fine star clusters and nebulas for binocular and telescope users. Let's take a look at two of the brightest clusters: M50 and NGC 2244 which is at the heart of the beautiful Rosette Nebula.

The amazing Rosette Nebula (NGC 2237) with NGC 2244 at its center recall the petals of a flower surrounding a cluster of stamens. The stars in our featured cluster were recently formed from the nebula's material. When their light switched on it set the hydrogen gas within the cluster's birth cloud to glow. Credit: Frank Barrett

NGC 2244 is a bit less than one outstretched fist to the left of Betelgeuse. Try pointing your binoculars at Betelgeuse and then sweeping due east. You'll soon run into a compact rectangular group of 7th and 8th magnitude stars. Although below naked eye brightness, these are bright enough to be seen individually in typical binoculars. If you think you glimpse a round puff of haze light surrounding the tiny stellar group you're seeing the Rosette itself. This nebula is excited to glow by ultraviolet light from the young stars in NGC 2244. A telescope shows lots of the Rosette's "petals" but its true gorgeousness is revealed only in long exposure photographs that shows curls and folds of hydrogen gas glowing vivid pink in the dazzling light of the central cluster. The cluster is only about 3 million years old -- hardly out of the barn as stars go. Consider that the sun is 4.5 billion years of age and only now reaching middle age.

The Rosette, which contains enough material to make 10,000 suns, and its hatch of newborns (NGC 2244) are about 4,500 light years away. With a diameter of 130 light years, this star-making machine is truly enormous. In comparison the Orion Nebula is only 24 light years wide. Future generations of sky watchers can expect to see new stars appear within this vast nebula that for us are still cocooned in obscurity.

M50 is a bright cluster easily visible in binoculars. It's 3,200 light years away and about 20 light years across. Credit: Ole Nielsen

Our next cluster comes from the catalog of the famous 18th century French astronomer Charles Messier. He discovered M50 in on April 5, 1772 from Paris with a small telescope back when Paris had dark skies. You can see it, too. In my 8x40 binoculars this weekend the cluster was a softly glowing patch of light with a bright little star on its southern edge. I could tease out several additional stars from the haze with close study. M50 is easy to find not quite one fist above Sirius almost in line with Procyon.

This is the galaxy M83 in Hydra and it resembles our spiral galaxy the Milky Way. We can look right into the disk of M83 and see many star-forming regions of pink hydrogen gas studded with clumpy star clusters (blue circles) They're extragalactic versions of the Rosette and Orion Nebulas. In addition I've marked a couple of clusters that have used up the gas in their nebular birth clouds. Credit: ESO

Standing and watching the stars and finding the constellations is an enjoyable activity. Getting to know a few additional characters in the sky like M50 and NGC 2244 adds an extra dimension to our viewing. Star clusters and nebulas are concentrated along the Milky Way because their homes are in our galaxy's spiral arms. The core of the galaxy formed first and used up much of its gas content long ago to create stars. Its home now to some of the galaxy's oldest stars. Later, material in the flat disk condensed to form the star clusters like the Pleiades, Hyades and our featured clusters. When we look into Monoceros our gaze takes us into the Milky Way's spiral arms into regions rich in new star formation.

Tomorrow we'll take a closer look at the Milky Way and another group of star clusters that look radically different from M50 and its ilk.

Posted by: rking@duluthnews.com on 3/9/2010 at 8:20 AM | Comments (2) | Permalink

Another fireball update plus a Saturnian sun

The sun near sunset yesterday was draped in a wreaths of clouds that mimicked the rings of Saturn. Hazy air scattered much of the sun's shorter wavelength light away -- the blues, greens and even some yellow -- leaving the disk a deep red. Photo: Bob King

Mercury and Jupiter were in conjunction only about a degree apart a short distance west of the sun yesterday evening. Unfortunately only the coronagraph on board the SOHO spacecraft could see the event, because the planets were so close to the sun they were lost in its glare.  A coronagraph uses a metal disk (dark blue circle) to artificially eclipse the sun so astronomers can study its outer atmosphere called the corona. Jupiter will reappear in the morning sky in just a couple weeks; Mercury makes one of its best appearances of the year at dusk later this month. More information on current planets is at bottom.

The coronagraph in the Solar and Heliospheric Observatory (SOHO) took this photo at 6:42 p.m. yesterday when the two planets were in conjunction (at their closest). The lines are electronic artifacts while the many white dots are stars. Credit: NASA/ESA

I've been in touch the past couple days with meteorite hunter Mike Bandli regarding the bright fireball seen over Duluth and region last Wednesday. Mike alerted me to the American Meteor Society's fireball sighting log. There I found more than a dozen additional reports on the meteor plus sightings of other recent fireballs. Most interesting, there were three reports of "distant rolling thunder" or rumblings associated with the Duluth fireball in the Stillwater-Lake Elmo-Hudson area east of the Twin Cities. Mike is now in the process of examining and interpreting NEXRAD (Next Generation Radar) Doppler data from the National Weather Service to look for possible detections of the fall. While rumblings are a good sign that pieces of the meteor may have survived, "the pressure wave is coming from much higher in the atmosphere and can be heard for much greater distances," according to Bandl. Translation: any potential fragments could be up to 100 miles from where the sounds were heard. I'll pass along more information as it comes to light.

Stars show as long trails during this 14-minute time exposure. Saturn (near top) is the brightest. Details: 70mm lens at f/2.8, ISO 200. Photo: Bob King

Yesterday evening was a perfect time to be out. We've grown so used to being cold while standing under the stars that I can't help but be amazed how relaxing and easygoing stargazing is when the temperature's in the 30s. I didn't even wear gloves. While peering through the telescope at Mars, comets and galaxies last night, my camera silently recorded the rotation of the Earth as revealed in the movement of the stars.

Tomorrow we'll revisit the constellation Monoceros the Unicorn and get acquainted with its brightest star cluster. Get your binoculars ready!


This week's planetary highlights include the improved visibility of Venus at dusk and Saturn coming into prominence in the evening sky. Illustration: Bob King

Posted by: rking@duluthnews.com on 3/7/2010 at 4:51 PM | Comments (0) | Permalink

Billion year odyssey

Two photos of the space station as it crossed the Belt of Orion last night about 6:45 p.m. Lars Waldner took the photo at left, I shot the other. We're only about five miles apart but notice the difference in their paths.

Orion's Belt was faintly visible last night when the International Space Station (ISS) passed by. These two photos were taken from the neighboring townships of Lakewood and Rice Lake. Even that small difference in distance was enough to noticeably alter the track of the ISS for each of us. Lars' photo shows a direct "hit" with the middle belt star Alnilam. He shoots, he scores!

Here are times for viewing the space station throughout the coming week weather permitting. If you live outside the Duluth region, just click HERE and type in your zipcode for times for your city. In all the passes listed below, the ISS will first appear in the western sky and move eastward across the northern sky. On the 10th-12th, if you have an open view to the northeast, you can use binoculars to watch the sun set on the station (it turns deep red) before it fades away in Earth's shadow.

* Tonight beginning at 7:07 p.m. A high, brilliant pass. It will cross the Bowl of the Big Dipper before fading out in the northeast.
* Monday March 8 at 7:32 p.m.
* Tuesday March 9 at 6:22 p.m. (another bright one) and again at 7:57 p.m. when it will first appear due north moving to the east.
* Wednesday March 10 at 6:47 p.m.
* Thursday March 11 at 7:12 p.m.
* Friday March 12 at 7:37 p.m.
* Saturday March 13 at 6:26 p.m.

This diagram shows all the stars within 12.5 light years of the sun. Sirius and Alpha Centauri are circled. Credit: Richard Powell

Everything is so far away in space. How do we grasp the meaning of stellar distances and time? Take the light year, a popular yardstick use to measure distances to other stars and galaxies. This is the distance that light, traveling at 186,000 miles per second, travels in one year. On the scale of the Milky Way galaxy one light year isn't very much yet it tallies up to 6 trillion miles. The nearest star beyond the sun is the Alpha Centauri system at 4.4 light years or about 26 trillion miles away. 26 trillion ... hmmm ... sounds about as meaningful as the deficit.

We can easily convert light years into time. Since light from Alpha Centauri takes 4.4 years to reach our eyes, the starlight we see tonight is 4.4 years old and left the star in late 2005. A more familiar star is the red supergiant Betelgeuse in Orion at a distance of  640 light years. When it winks at you tonight, those light rays started their journey around the year 1370 during the era of the Black Death or bubonic plague that wreaked havoc across Europe and the Middle East for decades. On the brighter side, the light from the Seven Sisters cluster tonight left just about the time Galileo pointed his first telescope at the heavens.

The core of the Corona Borealis Galaxy Cluster. The galaxies are the fuzzy, yellowish ovals. This cluster is probably the most distant galaxy cluster accessible to amateur astronomers . Credit: Jim Misti

Tucked into a corner of the distinctive constellation Corona Borealis the Northern Crown is a distant galaxy cluster cluster called Abell 2065, the Corona Borealis Galaxy Cluster. This dense cluster contains over 400 galaxies and depending on the source, is 1.1 to 1.5 billion light years away. On a recent night I was able to see only a half dozen of its many members, and they were all extremely faint. While I enjoyed the satisfaction of observing something so remote I needed a more tangible way to appreciate how ancient the light was that touched my retinas. That's when rocks came to the rescue.

In the Duluth and Lake Superior area, the crust of the Earth rifted or split some 1.1 billion years ago. Multiple flows of lava poured out from below and piled one atop the other until more they were more than 10 miles thick. The splitting eventually came to a halt and left a basin that was filled much later by glacial melt waters, some of which survives to this day as Lake Superior. Streams and rivers tumbling toward the lake cut through the ancient lavas exposing many of its layers in great cliffs and canyonlike walls.

An exposure of volcanic rock -- most likely rhyolite -- along Amity Creek is cracked into multiple layers from erosion. The rock poured out from fissures in our planet's crust over a billion years ago. Photos: Bob King

Last week I walked a frozen creek that passed several spectacular exposures of this once molten rock. Reaching out my hand to touch the cracked and crumbling layers, it struck me that this rock was laid down at nearly the same time that light from the Corona galaxies wended its way up the telescope tube to my eye. Man, that's old. I stood there for a while and let it all sink in. Galactic light had found its match in rocks that were literally in my own backyard. I may have been standing still but my thoughts were traveling faster than light through deep time.

Although we may never be able to truly appreciate the distances and time intervals the universe tosses our way, once in a while we're allowed a glimmer of the reality.

A very nice exposure of fractured volcanic rock. This wide view gives you a good idea of a typical river scene along Lake Superior's north shore.

Posted by: rking@duluthnews.com on 3/7/2010 at 9:56 AM | Comments (3) | Permalink