Stars over Sisters

Ancient skywatchers learned to recognize the night sky by associating certain arrangements of stars with objects familiar to them. These became the constellations. Cygnus the Swan, Orion the Hunter, and Taurus the Bull are three well-known examples.

But there is a small subset of constellations that depict more fanciful beings, such as a sea goat, centaur (half human-half horse creature), and flying horse. Our featured constellation for February is a member of this group.

Monoceros, the Unicorn, is visible from the Northern Hemisphere during most of the winter but is best viewed in early-to-mid February. Its location in the sky is easily determined because it lies near the center of the Winter Triangle, formed by the bright stars of Sirius, Betelgeuse, and Procyon. Being able to see Monoceros' constituent stars, however, will be a challenge since none are brighter than fourth magnitude. This means you'll need to find a dark area from which to see the single-horned critter in all its glory.

Surprisingly, Monoceros is not associated with any specific sky lore. It was originally named "Monoceros Unicornis" by Dutch astronomer and clergyman Petrus Plancius around 1612, apparently because the mythical animal appears several times in the Old Testament of the Bible.

Alpha Monocerotis is the constellation's brightest star, shining with a magnitude of 3.9. It is a "red clump" giant star, which means it's generating energy through helium fusion at its core. This luminary is twice as massive as our sun,10 times larger than its radius, and lies at a distance of 144 light-years.

While Monoceros is home to several fine deep sky objects, all of them are either open star clusters or defuse nebulae. The most visually striking of these is the Rosette Nebula and its associated star cluster NGC 2244. The Rosette Nebula is a vast stellar nursery where energetic stars that have recently formed are ionizing hydrogen atoms in the nebula, which is responsible for the red glow. The mass of the nebula is roughly equal to about 10,000 solar masses. This object is located 5,200 light-years away.