APOD 11: Open Star Cluster in Scorpius

2014 January 7

As one of the most prominent open clusters in the sky, M7 is dominated by blue stars, and can be seen by the naked eye in the dark sky as the tail of the Scorpion constellation. A dark dust cloud and millions of unrelated stars are towards the Galactic center are visible. M7 contains 100 stars, is 200 million years old,  spans 25 light years, and lies 1,000 light years away. M7 was observed by the ancients, in the time of Ptolemy, around 130 AD.