DSO of the Month :
Messier 3
AKA: NGC 5272
Position: 13 hr 42 min 12 sec +28 degrees 22 min 38 sec
Due south at 21.05 (BST) on 15 June 2022 – this is actually in daylight!
Messier 3
Image: Martin Gill, HAS member. Used with permission.
Messier 3, in the constellation Canes Venatici, is the third brightest globular cluster we can easily see in Havering. The brightest is M13 (DSO of the Month for June 2020) and the second brightest is M5 (June 2021). So what is the connection between globular clusters and June? Well, it is not just June – I have had globular clusters as DSO of the Month in the autumn as well. However if we consider globular clusters to be embedded in a sphere centered on the middle of the Milky Way, they either appear to us outside the galactic plane (as they are in the halo) and/or towards the centre of the galaxy. So they are most visible when the galactic plane (i.e. the Milky Way) is low in the sky and when we can observe Sagittarius; either way, the late spring and summer is the best time to see them. It was the fact that the globular clusters appear to be on one side of the sky that allowed Harlow Shapley to deduce in 1918 that the solar system is not close to the galactic centre. Furthermore globular clusters are perhaps the easiest DSOs to see in a twilight sky. It was the first Messier object to be observed by Charles Messier himself, on 3 May 1764, but the stars in the cluster were first resolved by William Herschel twenty years later.
Messier 3 is in the dark matter halo high above the galactic plane and lies a huge 32,600 light years away. Fortunately for us, it is also one of the most luminous and largest globular clusters with about half a million stars; a surprisingly large number of which are variable (274 at the last count). It is also fairly easy to locate, being roughly half-way between Cor Caroli or Alpha Canum Venaticorum (Double Star of the Month in May 2021) and Arcturus. It can be seen in binoculars, but is best viewed in a telescope.
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