M5

From South Dublin Astronomical Society

This globular of the summer sky is a little hard to find but your reward for doing so is the sight of one of the more showy objects of the Serpent. M5 can be found by sweeping ten degrees northwest of Mu Serpentis. The cluster appears a little broader than M13 in Hercules though not as bright. It looks like a luminous ball of cotton wool, showing a lustre in the centre that gradually fades towards the outer edges. The star 5 Serpentis is just to the east in the same field of view. M5 lies at a distance of 24,500 light years and is an extremely old globular cluster with an estimated age of 13 billion years. M5, as with all globulars, contains a number of RR Lyrae type variable stars. These are yellow giants with periods on the order of a day and are convenient yardsticks to determine the distances and distribution of the Milky Way’s globular family.