Explanation: M7 is one of the most prominent open clusters of stars on the sky. The cluster, dominated by bright blue stars , can be seen with the naked eye in a dark sky in the tail of the constellation of the Scorpion ( Scorpius ). M7 contains about 100 stars in total, is about 200 million years old , spans 25 light-years across, and lies about 1000 light-years away. The above deep image , taken last June from Hungary through a small telescope, combines over 60 two-minute exposures. The M7 star cluster has been known since ancient times, being noted by Ptolemy in the year 130 AD . Also visible are a dark dust cloud and literally millions of unrelated stars towards the Galactic center .