Adrian Dening's Stars Over Somerset

Wednesday, 7 May 2025 14:18

Monday 12th to Sunday 18th May 2025

Whenever astronomers talk about globular clusters, that can contain thousands to millions of stars bound together by mutual gravity, they always refer to the Great Globular Cluster in Hercules, also known M13 in the Charles Messier catalogue. There are other nice examples though and one in particular is well-placed in the night sky at the moment - M5 in the constellation of Serpens "The Snake".

If you aim your telescope towards the south around 1am in the early morning of Friday 16th, the cluster can be found below and to the left of the bright star Arcturus. You could try a little earlier in the night or earlier in the week, but we had a full Moon on Monday 12th and if you leave your observing until after 1am, then (what will be a waning gibbous Moon) will have risen above the horizon, creating lots of light pollution.

The cluster can be a little tricky to find. Firstly, the constellation of Serpens is unusual because it is split into two halves. The right hand part of the constellation goes by the wonderful name of "Serpens Caput". M5 is to the right of this, just above the star "5 Serpens".

The cluster was first observed as a fuzzy blob by German astronomer Gottfried Kirch while he was tracking a comet back in 1702 and Charles Messier added it to his list in 1764 so he wouldn't get fooled during his own comet-hunting activities. It wasn't until 1791 that the astronomer William Herschel identified individual stars within the cluster and counted 200 of them. The cluster is about 24,000 light years from us and heading away at a speed of 50Km/s. Although that sounds fast, in astronomical terms it isn't, so you'll be able to observe the cluster for a good few million years yet!