DSO of the Month
Messier 44 (Beehive Cluster)
Due south at 21.06 (GMT) on 15 March
Position: 08 hr 40 min +19 deg 59 min
Image by Martin Gill
One might assume that all star clusters are much the same, but even a casual inspection of the major star clusters shows that this is hardly the case. There are two major parameters with open star clusters: age and distance. If one compares the Beehive Cluster (M44) in Cancer with the Pleiades (M45) in Taurus, there are two obvious differences, the stars in the Pleiades look more blue and are brighter. It is brighter because it is nearer (450 light years against 607 for the Beehive, both taken from the latest Gaia data) and it contains hotter younger stars (mainly B spectral type) which is why it is also more blue. By contrast the Beehive contains mainly red dwarf (M) stars, white dwarfs and red giants, along with stars of spectral types F, G and K. This means it is older than the Pleiades (which are 115 million years old), but at 600 million years old, it is still much younger than our Sun which is 4.5 billion years old. The Beehive is roughly the same distance and age as the Hyades Cluster in Taurus and it is thought that the two clusters were formed from the same giant molecular cloud of gas. It is also one of the closest open clusters to the Sun.
With an apparent magnitude of 3.7, the Beehive Cluster is visible to the naked eye (although only barely so here in Havering) and has therefore been known since Classical times; it was mentioned by the famous astronomer Ptolemy as being in the breast of the Crab. It also has the Latin name Praesepe (meaning a stable or stall), as the Ancients saw the two neighbouring stars Asellus Borealis (Gamma Cancri or northern ass) and Asellus Australis (Delta Cancri or southern ass) as two asses eating from the same stall or manger. To find M44 look for two roughly fourth magnitude stars (lined up north-south) lying between Pollux in Gemini and Regulus in Leo, they are Asellus Borealis and Asellus Australis and the Beehive Cluster lies between them and slightly to the west (or right). A line between Castor and Pollux also points towards the Beehive. The cluster is fairly tight and rich, forming a roughly triangular shape, hence its modern name. It is about 1.5 degrees in diameter or three moon breadths so you will need low magnification in a relatively small telescope; a 16mm wide angle eyepiece (such as a Tele Vue Nagler) in an 80 or 90mm refractor will present a pleasing view of the cluster, showing the dimmer stars. Alternatively you could use binoculars, for example 10x50 or 20x80 binoculars would work well. It is one of these objects which also look very nice in the finder of your telescope.
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