Canis Major (Latin for 'greater dog') is a constellation in the southern hemisphere's summer sky and the northern hemisphere's winter sky. In the second century, it was included in Ptolemy's 48 constellations and is counted among the 88 modern constellations. Along with Canis Minor, it is commonly represented as following the constellation of Orion, the hunter, through the skies. The Milky Way passes through Canis Major. Several open clusters lie within its borders, including M41, which covers an area around the same size as the full moon. Canis Major contains Sirius, also known as the "dog star", the brightest star in the night sky and one of the closest stars to Earth. The other bright stars in the constellation are much farther away but very luminous. At magnitude 1.5, Epsilon Canis Majoris (Adhara) appears as the second brightest star of the constellation and is the brightest source of extreme ultraviolet radiation in the night sky. Next in brightness are the yellow-white supergiant Delta (Wezen), at magnitude 1.8, the blue-white giant Beta (Mirzam), at magnitude 2.0 and the blue-white supergiant Eta (Aludra), at magnitude 2.4. The red hypergiant VY Canis Majoris is one of the largest known stars, while the neutron star RX J0720.4−3125 has a radius of a mere 5 km (3 mi).
This illustration, which also features the constellations Lepus, Columba Noachi (now Columba) and Cela Sculptoris (now Caelum), was produced around 1823 and comes from Urania's Mirror, a set of 32 astronomical star chart cards.Lithograph credit: Sidney Hall; restored by Adam Cuerden