M 73 - Asterism in Aquarius



M 73 (NGC 6994) is an asterism in the constellation of Cepheus. It was discovered by Charles Messier in 1780. He identified It as a star cluster with some nebulosity. John Herschell did not observe any nebulosity and questioned its designation as a star cluster. However, he added this to his General Catalog. The debate about the true nature of M 73 continued into the 21st century. In 2000, a group of astronomers examined the color-luminosity relationship of the core stars and concluded that they were typical of an open star cluster. However, in 2002, M Odenkirchen and C. Soubiran noted that the distance of the stars were very different and were moving away from each other. The conclusion was that M 73 is an asterism vs. an open cluster.

M 73 is one of only three Messier objects that are not bonafide deep-sky objects. The others are M 40, a double star, and M 24, a patch of the Milky Way.


Telescope: Astro-Tech RC-8
Camera: Modified Canon 650D (T4i); ISO 1600
Mount:  iOptron CEM60
Guiding: QHY 5L-II on 60mm guide scope
Exposures: 12 @ 5min.
Notes:  Images were focused using the camera's live view and a Bahtinov mask. Exposures were captured, aligned and combined in ImagesPlus. The composite image was adjusted in Photoshop.
Taken from my backyard observatory in southeastern Minnesota on 8/31/21.
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