Monoceros is a faint constellation on the celestial equator. Its name means unicorn in Greek. Its definition is attributed to the 17th-century Dutch cartographer Petrus Plancius. It is bordered by Orion to the west, Gemini to the north, Canis Major to the south, and by Hydra to the east. Other bordering constellations include Canis Minor, Lepus, and Puppis.
Monoceros contains only a few fourth magnitude stars; making it difficult to see with the naked eye. Alpha Monocerotis has a visual magnitude of 3.93, while for Gamma Monocerotis it is 3.98.
Beta Monocerotis is a triple star system, the three stars forms a fixed triangle. The visual magnitudes of the stars are 4.7, 5.2, and 6.1. William Herschel discovered it in 1781 and called it “one of the most beautiful sights in the heavens.”
Epsilon Monocerotis is a fixed binary, with visual magnitudes of 4.5 and 6.5.
S Monocerotis, or 15 Monocerotis, is a bluish white variable star and is located at the center of NGC 2264. The variation in its magnitude is slight (4.2–4.6). It has a companion star of visual magnitude 8.
V838 Monocerotis, a variable red supergiant star, had an outburst starting on January 6, 2002; in February of that year, its brightness increased by a factor of 10,000 in one day. After the outburst was over, the Hubble Space Telescope was able to observe a light echo, which illuminated the dust surrounding the star.
Monoceros also contains Plaskett’s Star, which is a massive binary system whose combined mass is estimated to be that of almost 100 Suns put together.
The nearest known black hole to our Solar System is in this constellation. The binary star system A0620-00 in the constellation of Monoceros is at a distance of about roughly 3,300 light-years (1,000 parsecs) away. The black hole is estimated to be 6.6.