Canis Major (“greater dog”), situated to the south-east of Orion, is a southern hemisphere constellation that can be seen between November and April from both northern (winter) and southern (summer) latitudes. In Greek mythology, the constellation represents Orion the Hunter’s chief dog, Laelaps, who was so adept at hunting that he could catch any prey he pursued. Canis Major contains the night sky’s brightest star, Sirius (mag -1.46), which is a blue-white star located 8.6 light-years from the Sun.
Orion Family Constellation
Canis Major is part of the Orion family of constellations, which includes Orion, and his two hunting dogs (Canis Major, Canis Minor) pursuing a small hare (Lepus) through the night sky. In the early 17th century, a unicorn (Monoceros) was later added to the scene by Dutch astronomer Petrus Plancius.
The constellation has roots in many cultures, with the earliest mention recorded in an Ancient Mesopotamian tablet dating back to 1100 BCE. In the West, the best known of the ancient myths associates Canis Major with Laelaps, the faithful hound of Orion the Hunter, seen chasing Lepus the Hare across the sky, while to others Laelaps is helping Orion fight a giant bull represented by the nearby constellation Taurus.
By Roman times, the constellation came to represent the dog that Jupiter sent to guard the celebrated princess Europa whom he abducted while disguised as a white bull and carried off to Crete. There he impregnated her, and she later gave birth to King Minos, after whom the Minoan civilization is named. Likewise, the continent of Europe was named after the first queen of Crete, Europa.
– Sirius (Alpha Canis Majoris), the night sky’s brightest star, is located just 8.6 light-years away, making it the 5th nearest star to our own solar system. It appears blue white in color, although it might be called a rainbow star as it often twinkles with all the colors of the rainbow. Interestingly, the “dog star” is actually a binary system, with its primary component being Sirius A, a white main-sequence (A1V) star accompanied by a faint white dwarf (DA2) called Sirius B (The Pup). The distance separating the two stars varies from between 8.2 and 31.5 AU. To the naked eye, however, the two stars cannot be distinguished.
In ancient times, Sirius rising near the same time as the Sun (heliacal rising) represented the beginning of the Egyptian year, marked by the flooding of the Nile river. The period from 20 days before and after this occurrence was referred to as the “dog days” as ancient people believed that the heat of the “dog star” was added to that of the Sun to create the summer time’s hottest temperatures.
– Adhara (Epsilon Canis Majoris), is the second brightest star in the constellation, and with a visual magnitude of 1.5 is also the night sky’s 22nd brightest star. Located around 430 light years from the Sun, Adhara is a binary system whose main component is a blue giant star that is so bright that it if it were placed at the same distance as Sirius, it would appear 15 times brighter than Venus. The name ‘Adara’ derives from the Arabic for “the girls”, with the star representing one of Canis Major’s legs.
– Wezen (Delta Canis Majoris), the constellation’s third brightest star, is a yellow-white supergiant located 1,800 light years distant with a magnitude of 1.83. It is around 10 million year old, and has a luminosity 50,000 times that of our sun. Wezen means the “weight” in Arabic, with the star representing Canis Major’s hindquarter.
Other stars of interest in Canis Major includes Murzim, a blue white giant located 500 light years away whose name is Arabic for ‘the herald’; Audla , a blue supergiant variable star located 3,000 light years distant; and Tau Canis Major, an eclipsing binary star almost 3,200 light years away from Earth.
Deep Field Object
There are several deep-space object (DSOs) in Canis Major that will captivate the attention of any serious astronomer for hours on end. In fact, with the right viewing tools, one can see some of the most amazing objects in the night sky.
– Messier 41 is an open cluster 2,300 light years distant containing around 100 stars, many of which are red giants and white dwarfs. This Messier Object is around 26 light years across, and is estimated to be around 190 million years old.
– Canis Major Dwarf Galaxy, discovered in the year 2003, contains about a billion stars, and at 25,000 light years distant is now believed to be the closest galaxy to our solar system, although its galaxy status is still disputed. It is also located 42,000 light years from our galactic center, but is is difficult to see because it lies behind the Milky Way’s plane of sight.
Other objects of interest in the constellation includes the two spiral galaxies NGC 2207 and IC 2163, which are currently colliding around 130 million light-years away; and Thor’s Helmet (NGC 2359), a small emission nebula over 15,000 light years away that has formed around an extremely hot star thought to be in its pre-supernova stage.
Do yourself a favor, and check out this classic constellation during your next stargazing outing. The mythology of the constellation may draw us in, but the sights that can be found in the group of stars is nothing short of amazing.