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Astronomical Observatory: Cool Images

Astr110 Photography Projects, Fall 2006

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M72, Nate Kamerman


Discovered by Pierre Mechain in 1780, the star cluster M72 is not a new find in the astronomy world, nor is it an overly popular entity. Strangely enough, because it is a hard cluster to visualize, it was considered to be a nebula rather than a cluster for a long period of time. Indeed, this would have been an easy mistake to make, seeming how the cluster is made up of rather faint stars. (The brightest ones only have a magnitude of 14.2) Being an old cluster, M72 is comprised primarily of old stars, giving it a yellow appearance. However, M72 is fascinating in that it contains several blue giants, which are relatively young stars. In other words, the typical star in this cluster is old, not new, thus creating the question of why stars appearing to be young are seen here. Some stellar theorists believe that these globular blue giants may be the result of two old stars that have merged rather than a new star. Despite the fact that it is not the biggest, brightest, or most popular cluster, (it only has a diameter of roughly 47 light years) and is not very close, (53000 light years) M72 is still a fascinating part of the cosmos.

Within the image that I have taken, you can visualize roughly 800 individual stars. However, it has been predicted that this cluster has more than 100,000 stars. The reason that one can only see a small portion of the actual number of stars within this cluster lies in the fact that the brighter stars drown out the dimmer ones. The light from the bright star will combine with or out illuminate the light from the dim one. This also explains why the center of the cluster seems so much brighter than the rest of its surrounding stars. The center seems bright because it is the combination of light from so many different stars rather than individual stars.


Right Ascension (J2000) 20:53:30
Declination (J2000) -12:32:00
Filters used blue(B), green(V), red(R), and clear(C)
Exposure time per filter 5x60 seconds
Date observed






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