M7

From South Dublin Astronomical Society

M7
Type	Open cluster
NGC	NGC 6475
Constellation	Scorpius
Right Ascension	17h 53.9m
Declination	-34° 49’
Magnitude	3.3
Size	80 arc min.
Image:M7 messier image.jpg

Poised above the raised stinger of the celestial scorpion is M7, a star cluster that has been known since ancient times when the Greek astronomer Ptolemy called it the “nebula following the sting of Scorpius”. Indeed, the ancient Arabs called M7 the “venom of the Scorpion” and the description is rather apt. The group is visible to the naked eye from temperate and more southerly latitudes. The cluster is more loose than nearby M6 — the diameter of the group is over a degree in extent — and a little under half of its 80 member suns are visible in binoculars. The field in which it is located is quite rich in faint stars. The brightest star in M7 is a magnitude 5·6 G-type sun. M7 lies about 800 light years away (though some sources quote 1,000 light years) with an estimated age of 220 million years.