Ptolemy Cluster

M7, the Ptolemy Cluster, is a large, bright open cluster near the tail of Scorpius. The astronomer Ptolemy described it nearly 2,000 years ago as a nebulous patch, one of the earliest recorded deep-sky objects.

It is about 1,000 light-years away and contains around 80 bright stars spread across an area larger than the full Moon.

From mid-northern latitudes it stays low in the south, but from the Southern Hemisphere it rides high on winter evenings against the rich star clouds of the Milky Way.

M7 is around 200 million years old and roughly 25 light-years across. Charles Messier added it to his catalog in 1764 as the seventh entry.

It is the southernmost object in the Messier catalog, which is why it always appears low from Europe and the northern United States.

Under dark skies, the dark lanes of the Milky Way around M7 add to the view, making the cluster look like a bright island in a river of faint stars.