Monoceros
When chastity was a heavenly virtue, don’t you know
Our winter sky is (quite justifiably) dominated by Orion, club raised and shield forward, he takes on the mighty bull, Taurus and the not so mighty hare, Lepus. However, like every over confident hunter, Orion seems to be unaware of the creature that is following him, tracking his every movement across the celestial sphere. That creature is Monoceros, the Unicorn, and what a prize for any hunter, if only the poor guy turned round.
So a Unicorn? You might ask whether those sensible, Gorgon loving Greeks had gone a step too far here. Well no, they played no part in it. Monoceros was “invented” in the 1690’s (a bad decade for witches as I recall) although some reports date the constellation to earlier (possibly even Persian) times. As such it has no associated mythology, although perhaps placing the elusive and much sought after creature so close to Orion could be seen as something of a slight against the stories of old.
Stellar Sights
As noted above, Monoceros, compared to its bejewelled neighbours is a dim constellation, often lost in the suburban glow inflicting every horizon in Durham. Its brightest star, Alpha Monocerotis, a magnitude 3.93 star, is dimmer than all but one of the main stars of Orion (Upsilon Orionis is magnitude 4.62) and yet it has some interesting targets.
Beta is a triple system, described by William Herschel as ‘one of the most beautiful sights in the heavens’. The three white stars range from magnitude 4.7 to 6.1 and are arranged in what appears to be a fixed triangle.
Epsilon is a fixed double with, again, nicely balanced primary and secondary stars.
Plaskett’s Star is a massive spectroscopic binary and is seen as the head of the Unicorn. First observed by (surprise surprise) Mr Plaskett in 1922 these are the largest pair of stars in our galaxy so far discovered with masses roughly 40 and 60 times our sun. The two blue-giants taken together are 3000 times brighter than sol.
Into the Deep
This region, seemingly typical of any that sits close to the horizon, is rich in deep sky objects, for the most part open clusters which sit in amongst the beautiful background of the Milky Way. Here are a four of the more prominent ones.
M50 is the only Messier object in the constellation and is an open cluster deep in the beautiful sweep of the Milky Way. Lying 3200 light years away from Earth it is fairly compact and has something of a heart shaped figure. It is comprised mostly of blue-giants but also contains a single red giant and a scattering of yellow giants.
To the north of the main stars lies NGC 2264; the Christmas Tree Cluster and the associated Cone Nebula. The Christmas Tree has its base at 15 Monocerotis (a variable star) with a 7th magnitude star at its peak – the layout of the stars between these two forming the triangular shape of the tree. The Cone Nebula is in this region but like the Horsehead in Orion is elusive and unlikely to be seen in the society scopes. Nebulosity should be apparent around 15 Mon as this is a region of dense star forming matter.
NGC 2232 is another open cluster of stars surrounding the magnitude 5.1 10 Monocerotis. This is a pleasant sight in binoculars but should also look good in the scope with a good night bringing out deeper layers of stars in the background.
Finally NGC 2244, the Rosette Cluster, is located at the heart of another dense star forming region called the Rosette Nebula. Although the Nebula cannot be seen without a good sky and some form of filter (O-III is preferred) the cluster should be visible and is a group of stars newly formed from the nebulous material. Star forming is still going on in this region and a new-born star was discovered as recently as 2004.
That concludes my brief look at the Unicorn – a constellation easily overlooked but one that holds many hidden treasures.