DSO of the Month
: Messier 5
AKA: NGC 5904
Position: 15 hr 18 min 33.2 sec +02 deg 04 min 52 sec
Due south at 21.06 (BST) on 15 June 2021 (actually in daylight!)
Messier 5
Image: Les Brand
It might surprise you to learn that M5 is about as bright as the better known globular cluster M13 in Hercules (the listed magnitude of M5 varies a great deal but it is about 5.9 or about the same as M13). There are brighter globular clusters but they are either in the southern hemisphere completely (Omega Centauri, 47 Tucanae) or are extremely low down in Havering (M22, M4). It is interesting to compare M5 with M13. M5 is slightly larger as seen in the sky, but is slightly smaller in reality (80 light years in radius against 84 light years for M13). Despite being smaller, M5 is 40% heavier than M13. They are roughly similar distances from us, M5 being 24,500 light years and M13 is 22,200 light years. The major difference between them is that M13 is significantly older than M5 being 11,650 million years old against M5’s 10,620 million years. M5 contains a significant number of RR Lyrae variables (see Star of the Month for July 2020). M5 was discovered by the Berlin astronomer Gottfried Kirch while he was observing a comet in 1702 and Charles Messier included it in his list in 1764. William Herschel was the first astronomer to resolve the individual stars in M3 in 1791. M3 can be found roughly halfway between Alpha Serpentis (Unukalhai) and Mu Virginis, a rather faint star in the easternmost part of Virgo and above Beta Librae (Zubeneschamali).
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