Like the fabled unicorns, Monoceros is hard to spot, notable only for its deep-sky objects and not for its stars.
The Mythology of Monoceros
Monoceros is positioned in the sky sneaking up on Orion. Because it is a unicorn, considered a magical creature, Orion has not heard it approaching. Actually, the history of the "Unicorn in the Sky" is not as old as the other mythological creatures it surrounds. The first known reference to Monoceros is on a 1624 star chart.
Finding the Unicorn in the Sky
Monoceros is located directly east of Orion, spanning almost the entire height of the great Hunter. It is a star-poor region that is surrounded by many great stars, including the stars of Orion, the brightest star in the sky, Sirius, below it, and Procyon to its east.
Observing Targets in Monoceros
What the Unicorn lacks in bright stars it makes up for in interesting deep-sky objects. The Milky Way flows directly through this region of the sky.
The first great target lies between Orion's Betelgeuse and Canis Minor's Procyon. (It's about twice as close to Betelgeuse than Procyon.) Here you will find the 4.8 magnitude Rosette Nebula, NGC 2244. This cluster and nebula lie about 5,200 light-years from Earth. They are a popular target, being easy to find in smaller telescopes and having a beautiful rose-like shape. You can even try picking it up in binoculars.
Just over five degrees above the Rosette is the magnitude 3.9 Christmas Tree Cluster. This open cluster with some nebulosity is also referred to as the Cone Nebula, or NGC 2264. Does it look like a lit-up Christmas tree to you?
Just one degree from the Christmas Tree Cluster heading back in the direction of the Rosette Nebula is Hubble's Variable Nebula, NGC 2261. This unique object is best seen in professional photographs, where the comet-like appearance of a star and its streaming nebula can be seen.
The only Messier object in Monoceros lies in the southern portion of the constellation. M50 is a magnitude 5.0 open cluster. It lies about 3,000 light-years away and its gathering can be seen through small telescopes.
Below M50 and on the border with Canis Major is a large nebula known by various names. IC 2177, the Gum 1 Nebula, and the Seagull Nebula all describe this large patch of gas and dust. The Seagull name comes from the objects wide-spread wing-like stretches of dust plus a round ball-shaped area of nebulosity on top. Look for the dark lane that separates the cuts into the head area. The stars in this region shine at about 8th and 9th magnitudes.
(Rosette Nebula image in Hydrogen Alpha: Image based on data obtained as part of the INT Photometric H-Alpha Survey of the Northern Galactic Plane, prepared by Nick Wright, University College London, on behalf of the IPHAS Collaboration.)
