Astro Bob A look at celestial happenings in the Northland and beyond Bob King View my profile Click here to view previous posts or additional resources

The 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.

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

Tags: daily updates, astro bob, life, cancer, zodiac, m44, beehive, m67, mars, coelacanth