M 7

The Scorpion's Tail
(Ptolemy's Cluster) in Scorpius

"M7 is a large and brilliant group, easily detected with the naked eye... the cluster is seen projected on a background of numerous faint and distant Milky Way stars. "(Burham).

This splendid cluster was known to Ptolemy who mentioned it about 130 AD, who described it as the "nebula following the sting of Scorpius". The description may also include M6 but this is uncertain.

M7 consists of 80 stars brighter mag 10 in a field of about 1.3 degrees apparent diameter which at its distance of perhaps 800 light years corresponds to a linear extension of 18 light years. This group is receding from us at 18 km/sec. The brightest star is a yellow giant, the hottest main sequence star is of spectral type B6. M7's age was estimated at 220 million years.

Right ascension	17 : 50.7 (hours : minutes)
Declination	-34 : 48 (degrees : minutes)
Distance	1.0 (light-years*10^3)
Visual magnitude	4.1