M6

From South Dublin Astronomical Society

M6
Type	Open cluster
NGC	NGC 6405
Constellation	Scorpius
Right Ascension	17h 40.1m
Declination	-32° 13’
Magnitude	4.2
Size	25 arc min.
Image:M6 messier image.jpg

This cluster, combined with M7 on the next page, are probably the ultimate challenge objects in the binocular handbook because of the rare opportunities you may get to snare each of the two. Their low altitude from Ireland may even necessitate a trip to our south coast where you’ll also need very good sky conditions. M6 appears as a compact group with two trails of stars leading from the centre — this pattern is what has given the group its nickname. The (sometimes) brightest star here is the semi-regular variable BM Scorpii which flickers between magnitudes 6·8 and 8·7 in a period of 850 days. About 80 stars are members of M6 and the cluster is fairly close to us at only some 1,600 light years. It was first discovered by the Sicilian astronomer Giovanni Hodierna (1597-1660).