Brecher-Rosette Nebula
The beautiful Rosette Nebula may be the best known deep-sky attraction in Monoceros. (Ron Brecher

Treasures in Monoceros

Although often overlooked, the celestial unicorn has its share of delights.

Over the Christmas holidays I chatted with SkyNews associate editor Ken Hewitt-White. We agreed that the constellation Monoceros, the unicorn, is among the most overlooked regions of the sky. The problem is that it has no bright stars — a decided handicap given its position adjacent to the showy constellations Orion, Gemini, Canis Major and Canis Minor. Indeed, much of Monoceros is framed by the great winter triangle of Betelgeuse, Sirius and Procyon. What constellation wouldn’t pale in that company? So what does Monoceros have to tempt us away from its brilliant winter neighbours? Let’s have a look.

Brecher-Rosette Nebula
The beautiful Rosette Nebula may be the best known deep-sky attraction in Monoceros, but it’s a visually challenging sight. However, the cluster at its centre (NGC2244) is a lovely object suitable for small telescopes. (Ron Brecher)

The main attractions in Monoceros are located in a region lying about halfway between the stars Betelgeuse in Orion, and Procyon in Canis Minor. Here you’ll find objects that delight in telescopes of all sizes. The most northerly highlight is NGC2264, a stunning cluster of several dozen stars that, depending on its orientation, looks like a Christmas tree, hence its nickname, the Christmas Tree Cluster.

A few degrees south of NGC 2264 you’ll find an equally attractive grouping, NGC2244. In my 120-millimetre Orion EON refractor at 64×, its principal stars form a structure that, for all the world, looks  like the scaffolding that supported William Herschel’s large reflectors in the early 19th century. This cluster is immersed in the famous Rosette Nebula (NGC2237-2238). Unhappily, I can’t report ever seeing the nebula from my suburban location despite having tried various eyepieces and filters. But I’m sure it would be a snap under dark skies.

Monoceros chart

Monoceros also plays host to the 50th entry in Charles Messier’s famous catalogue. M50 resides in the constellation’s southern extremities, several degrees below the celestial equator. Why Messier included this rather pedestrian cluster and ignored the other two I’ve highlighted is a mystery. M50 is easy to find, though, about eight degrees north-northeast of Sirius.

I’ve saved the best for last — Beta (β) Monocerotis. It’s one of the most spectacular multiple stars in the sky. With my refractor at 82×, I can barely split the main star into two components, just three arc seconds apart. The third member of this little family lies seven arc seconds to the northwest. To quote the aforementioned William Herschel, Beta is “one of the most beautiful sights in the heavens.”

Three clusters, an elusive nebula, and a fine multiple star — not a bad haul for such an overlooked corner of the winter sky!

David A. Rodger was the first Director of the HR MacMillan Planetarium in Vancouver and is a life-long amateur astronomer who observes the sky from his North Vancouver townhouse.