Before it was a dog, Canis Major was a Babylonian bow and arrow
The Greeks saw a hound trotting after Orion. Babylonian skywatchers around 1100 BC saw a weapon instead: Sirius was an arrow aimed at the hunter, and stars to its south formed the bow. Chinese astronomers kept a similar picture, with a celestial bow pointing at Sirius, though for them the bright star was a wolf.
Canis Major, the Greater Dog, was one of Ptolemy's 48 constellations and survives among the modern 88. In Greek myth it was sometimes Laelaps, a hound given by Zeus to Europa, or a dog so fast that Zeus placed it among the stars; most often it was one of Orion's hunting dogs, chasing the hare. Other peoples told their own stories: the Māori grouped it with neighbouring stars as the Assembly of Rehua, and among the Merazig of Tunisia its stars herald two weeks of hot weather.
Its centrepiece is Sirius, the brightest star in the night sky and one of the nearest at 8.6 light years, which explains much of its glare. Its name comes from the Greek for scorching, and it underpinned the ancient Egyptian calendar. Sirius is actually a pair; its companion, a white dwarf about ten thousand times fainter, circles it every 50 years. Mirzam, whose name means the announcer, rises just before Sirius and so heralds it.
Most other bright stars here are distant giants. Wezen, about 1,600 light years away, is 50,000 times as luminous as the Sun and so large that, placed at the Sun's position, it would reach Earth. Only about 10 million years old, it has already exhausted the hydrogen in its core and should become a red supergiant within 100,000 years before eventually exploding. Adhara is the sky's brightest source of extreme ultraviolet light, and the red hypergiant VY Canis Majoris is among the largest stars known.
The dog's brilliance shifts over deep time. Adhara outshone every other star in our sky about 4.7 million years ago, and Mirzam did so a few hundred thousand years later. In roughly 2.87 million years, another member, NR Canis Majoris, is expected to reach its peak brightness. At the opposite extreme, a neutron star in the constellation measures a mere 5 kilometres in radius.
Source: Canis Major
