APOD: 3/12/13 – Messier 72

Joshua FilmerMarch 12th 2013
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This is the globular cluster known as Messier 72 (also known as M72 or NGC 6981). This object is about 54.5-thousand light-years away and can be found within the constellation Aquarius.


M72 has an interesting history regarding its discovery and classification. It was originally discovered in 1780 by Pierre Mechain. Shortly afterwards, Charles Messier included it in his list of objects now known as “Messier Objects.” Since this structure is faint and compact, both people originally categorized M72 as a nebula. It wasn’t until the twentieth century that M72 was correctly reclassified as a globular cluster.


Globular clusters are the oldest structures in the galaxy. Once upon a time, thousands of these objects roamed the Milky Way. Through frequent encounters with other globular clusters, the galactic center, and galactic collisions, 200 or fewer are all that remain of these fantastically packed objects. Many globular clusters contain an upwards of a million stars. M72, on the other hand, is relatively small and is only about 168,000 times the mass of the Sun, while the core has a luminosity of about 2.3 that of the Sun’s. To date, there are only 43 identified stars seen in NGC 6981

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