M7 - Ptolemy's Cluster
Credits: Keith Turnecliff, Nerja, Spain
M7, also known as Ptolemy’s Cluster, is a bright open cluster in Scorpius constellation. The cluster lies at an approximate distance of 980 light years from Earth. It has the designation NGC 6475 in the New General Catalogue. With a visual magnitude of 3.3 and an apparent diameter of 80 arc minutes – more than twice the apparent size of the full Moon – Ptolemy’s Cluster is an easy naked-eye target.
Facts about M7 by Keith Turnecliff
The best time of year to observe M7 is in the summer months. Because of its large size, the cluster is best seen in binoculars.
Messier 7 is believed to be about 220 million years old and has a mass about 735 times that of the Sun. It is approaching us at a speed of 14 km/s.
The brightest star in M7 is a yellow G8-type giant with an apparent magnitude of 5.6.