Canis Minor is an ancient constellation which represents the smaller of Orion’s two hunting dogs (although it was also described as the uncatchable fox pursued by the unbeatable dog). Its historical significance lay in its brightest star Procyon heralding the heliacal rising of Sirius in the dawn sky, Procyon being Ancient Greek for “before the dog”. Procyon is a magnitude 0.4 F type star which is relatively close at 11.5 light years and, like Sirius, it has a white dwarf companion, which is too close to be resolved in a small telescope. There are no deep-sky objects in the constellation, but it has a wide double, DD Canis Minoris (STTA 88) [1]. The stars are both white and are magnitudes 7.5 and 8.9. They are a binary system; the third member is a faint (mag. 10.9) line of sight star.

Monoceros (the Unicorn) has an unusual origin. Petrus Plancius (Pieter Platevoet), who was born in Flanders but moved to the Netherlands to escape Spanish rule, introduced a number of constellations between 1597 and 1612, some in the southern hemisphere and some in the northern hemisphere. Of his northern hemisphere constellations, only Monoceros and Camelopardalis have survived. Monoceros survived partly because it was accepted by the Polish astronomer Johannes Hevelius in 1690. Plancius was a cartographer and a minister of the Dutch Reformed Church. He may have introduced the Unicorn as a symbol of Christian purity. It is a faint constellation; the brightest star Alpha Monocerotis is magnitude 3.9, and the other stars are fourth or fifth magnitude. Hence it is practically invisible in Havering. None of the (relatively) bright stars in Monoceros have been given a name by the IAU and the lettering of the stars (Alpha, Beta, etc.) was done by Benjamin Apthorp Gould in the nineteenth century, not Johann Bayer.

While its stars may be faint, Monoceros does contain a number of interesting objects. In the north of the constellation is the Christmas Tree Cluster (NGC 2264) [2], which is magnitude 3.9 and 2,400 light years away. At the base of the “tree” is the hot energetic star 15 (or S) Monocerotis, which is magnitude 4.7 and has a companion which is 7.8, but it is a tight pair (2 arcsec). This area also contains the Cone Nebula, but this is difficult to see visually. Just below the Christmas Tree Cluster is another variable: R Monocerotis (mag. 11.9), which is a very young star with a circumstellar disc of dust and gas. It is at the base of Hubble’s Variable Nebula (HGC 2261) [3], a diffuse nebula (mag. 9) which is illuminated by the star. Further down still is NGC 2244 (Caldwell 50) [4], a young star cluster which is magnitude 4.8 and about 5,300 light years distant. It has a foreground star 12 Monocerotis (mag. 5.9) and two bright O type stars. The cluster is embedded in the often imaged HII emission nebula known as the Rosette Nebula, but this is very difficult to see visually.

Even farther south, above Beta Monocerotis, is NGC 2232 [5] which is bright (mag. 3.9), but often overlooked. Just over 1,000 light years away, it is one of the closest star clusters to us. Messier 50 [6] is a small star cluster on the southern edge of the constellation and is comparatively faint at magnitude 5.9; it is 3,300 light years away. Finally, Messier 48 [7] is in Hydra, but is considered here as it is closer to Monoceros than the main body of Hydra. It is magnitude 5.8 and is 2,500 light years distant. At about 450 million years old, it is a middle-aged cluster.

V640 Monocerotis (Plaskett’s star) [8] is a magnitude 6.1 spectroscopic binary discovered by the Canadian astronomer John Plaskett in 1922, which was thought to be the most massive binary star system known, until it was decided around the turn of the century that Eta Carinae was a binary system as well (and more massive). They are both O type stars and the system is 5,250 light years away. The two main double stars in Monoceros are Beta and Epsilon Monocerotis. Beta (or 11) Monocerotis is a triple of relatively bright white stars (mag. 4.6, 5.0 and 5.3) which are close together in a fish-hook shape. They probably gravitationally bound, but it is not certain. William Herschel considered it to be one of the most beautiful sights in the night sky. Epsilon (8) Monocerotis is an easy pair of stars (mag. 4.4 and 6.6) which are yellow-white and pale blue; it is a binary system. Struve (STF) 1183 [9] is a lemon-yellow and blue pair (mag. 6.2 and 7.8) which is very wide.