M7 - Open Star Cluster in Scorpius

M 7 is commonly known as the Ptolemy Cluster, named after the Greek-Roman astronomer who first recorded it in 130 AD. He described it as a nebula. In 1654, the astronomer Giovanni Battista Hodierma noted that this object was a star cluster, counting 30 stars in it. Charles Messier added this to his catalogue in 1764.

With a declination of - 34.8, M 7 is the southern-most of the Messier objects. It lies 980 light years away and spans 25 light years. It is known to contain 80-100 stars and at a combined magnitude of 3.3, it is easily visible to the naked eye.

Taken at the Nebraska Star Party on 8/1/16.


Telescope: Sky-Watcher 120ED
Mount: Sirius EQ-G
Camera: Modified Canon 650D; raw capture; ISO 800
Exposures:  16 @ 3 min.
Note: Camera was focused using a Bahtinov mask and live view. The subframes were aligned and combined in ImagesPlus. The composite image was adjusted in Photoshop. Topaz DeNoise was applied to reduce grain.
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