Monoceros, constellation in the northern sky at about 7 hours right ascension and on the celestial equator in declination. Its brightest star is Alpha Monocerotis, with a magnitude of 3.9. This constellation contains R Monocerotis, a young star immersed in a nebula. In 1612 Dutch cartographer Petrus Plancius introduced this constellation on a celestial globe he made and represented it as a unicorn. Because this area of the sky contains only faint stars, it had not been ascribed to a constellation earlier.