Tuesday, July 26, 2011

Globular Cluster Photo Series (Part 8): M72

Today I have a picture of Messier 72 for your perusal. This is one of the farther clusters from us, at a whopping 55,000 or so light years (keep in mind that the Milky Way galaxy is about 100,000 light years or so in diameter, or roughly six hundred quadrillion miles). It is located in the direction of the constellation Aquarius, which combined with its great distance places it on the far side of the galactic core from us. It's the smallest cluster in apparent angular size we've looked at so far at a miniscule 6.6 arcminutes in diameter, about a fifth as wide as the full Moon.

Messier 72 in Aquarius.
While it appears faint to us, the great distance of M72 means that it is actually one of the more intrinsically luminous globular clusters out there. At 106 light years in diameter it's fairly average sized, but has an unusually large number of variable stars, at least 44. It's also one of the least concentrated clusters, by which I mean that it has a very even distribution of light instead of a much brighter spike in the middle (look back at earlier pictures to see examples of more concentrated clusters). And other than that, there's not much for me to say about it except that I still think it's kind of pretty.

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