|Pronunciation||/ /, genitive / /|
|Symbolism||the greater dog|
|Right ascension||7 h|
|Area||380 sq. deg. (43rd)|
|Stars with planets||6|
|Stars brighter than 3.00m||5|
|Stars within 10.00 pc (32.62 ly)||1|
|Brightest star||Sirius (α CMa) (−1.46m)|
|Nearest star||Sirius (α CMa)
(8.60 ly, 2.64 pc)
|Visible at latitudes between +60° and −90°.
Best visible at 21:00 (9 p.m.) during the month of February.
Canis Major / / is one of the 88 modern constellations, and was included in the 2nd-century astronomer Ptolemy's 48 constellations. Its name is Latin for 'greater dog', and is commonly represented as one of the dogs following Orion the hunter (see also Canis Minor the 'lesser dog'). Canis Major contains Sirius, the brightest star in the night sky, known as the 'dog star'. It is bright because of its proximity to our Solar System. In contrast, the other bright stars of the constellation are distant luminous bright giants and supergiants. At magnitude 1.5, Epsilon Canis Majoris (Adhara) is the second brightest star of the constellation, followed by Delta (Wezen) at 1.8, Beta (Mirzam) at 2.0 and Eta (Aludra) at 2.4. The red hypergiant VY Canis Majoris is one of the largest stars known.
Canis Major is a constellation in the southern hemisphere's summer (or northern hemisphere's winter) sky, bordered by Monoceros (which lies between it and Canis Minor) to the north, Puppis to the east and southeast, Columba to the southwest, and Lepus to the west. The three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is 'CMa'. The official constellation boundaries, as set by Eugène Delporte in 1930, are defined by a polygon of 4 sides. In the equatorial coordinate system, the right ascension coordinates of these borders lie between 06h 12.5m and 07h 27.5m, while the declination coordinates are between -11.03° and −33.25°. Covering 380 square degrees, it ranks 43rd of the 88 constellations in size.
Johannes Bayer used the Greek letters Alpha through to Omicron to label the most prominent stars in the constellation, with Bode later adding Sigma, Tau and Omega. Lacaille added lettered stars a to k but none are in use today. John Flamsteed numbered thirty one stars, with 3 CMa being placed by Lacaille into Columba as Delta Columbae (Flamsteed had not recognised Columba as a distinct constellation).
Canis Major is a very prominent constellation because of its many bright stars. These include Sirius (α Canis Majoris), the brightest star in the night sky, as well as three other stars above magnitude 2.0.
Alpha Canis Majoris, commonly known as Sirius, is the brightest star visible in the night sky at magnitude −1.44, and is one of the closest stars to Earth at a distance of 8.6 light-years. Its name comes from the Greek word for "scorching" or "searing". It is a variable star, with a variation of approximately 0.1 magnitude; this variability was discovered by the Hipparcos satellite. Sirius is also a double star; its companion is called Sirius B, which has a magnitude of 8.4. The two orbit each other every 50 years. Their closest approach last occurred in 1993 and they will be at their greatest separation between 2020 and 2025. Sirius was the basis for the ancient Egyptian calendar. It is part of the asterism known as the Winter Triangle in the Northern Hemisphere, or the Summer Triangle in the Southern. The star is also recognized as Canis Major's nose.
Flanking Sirius are Beta and Gamma Canis Majoris. Also called Mirzam or Murzim, Beta is a blue-hued pulsating variable star of magnitude 2.0, which varies by a few hundredths of a magnitude with a period of 6 hours. Mirzam is 500 light-years from Earth, and its traditional name means "the announcer", referring to its position as the "announcer" of Sirius, as it rises a few minutes before Sirius does. Gamma is a much fainter star of magnitude 4.11, in reality a blue-white bright giant 402 light years from earth.
Epsilon Canis Majoris, also called Adhara, is the second brightest star in Canis Major and the 23rd brightest star in the sky. It is a blue-hued giant star of magnitude 1.5, 430 light-years from Earth. It is a binary star; the secondary is of magnitude 7.4. Its traditional name means "the virgins". Nearby is Delta Canis Majoris, also called Wezen. It is a white-hued supergiant star of magnitude 1.8, 1800 light-years from Earth. Its traditional name means "the weight". Eta Canis Majoris, also called Aludra, is a blue-hued supergiant star of magnitude 2.4, 3200 light-years away. Nestled between Adhara and Wezen lies Sigma Canis Majoris, known as Unurgunite to the Boorong people, a red supergiant 1,120 light years away of apparent magnitude 3.41. To the west of Adhara lies Zeta Canis Majoris or Furud, a 3.0 magnitude star which is actually a spectroscopic binary.
North of Sirius lie Theta and Mu Canis Majoris. Mu is a yellow-hued giant star of magnitude 5.0, 900 light-years away. It is a double star; the secondary is a blue-white hued star of magnitude 7.0. Nu Canis Majoris is a yellow-hued giant star of magnitude 5.7, 278 light-years away; it is at the threshold of naked-eye visibility. It has a companion of magnitude 8.1.
Canis Major is also home to several variable stars. Tau Canis Majoris is an eclipsing binary. UW Canis Majoris is a Beta Lyrae variable star 3000 light-years from Earth. It is an eclipsing binary that ranges in magnitude from a minimum of 5.3 to a maximum of 4.8. It has a period of 4.4 days. R Canis Majoris is another eclipsing binary.
VY Canis Majoris is one of the largest stars known, a remote red hypergiant of apparent magnitude 7.5.
There are not many bright deep-sky objects in Canis Major. Its only Messier object is M41 (NGC 2287), an open cluster of visual magnitude 4.5, 2100 light-years from Earth. It is noted for being particularly large and bright—it contains approximately 80 stars in an area of 0.5 square degrees, the size of the full Moon, and is visible to the naked eye—M41 was mapped by the ancient Greeks. The open cluster has many orange-hued giants, the brightest of which are of the 7th magnitude. Canis Major also features another noteworthy open cluster, NGC 2362, a small, compact grouping, 5200 light-years from Earth. It contains about 60 stars, the brightest of which is τ Canis Majoris, a blue giant of magnitude 4.4.
The band of the Milky Way goes through Canis Major and therefore background galaxies are hidden behind interstellar dust clouds. However, in 2003, Canis Major Dwarf, the closest satellite galaxy to Earth, was found within the constellation.
Sirius, its brightest star, means "scorching star", since the summer heat occurred just after Sirius' heliacal rising. The Ancient Greeks referred to such times in the summer as dog days, as only dogs would be mad enough to go out in the heat, leading to the star being known as the Dog Star. Consequently, the constellation was named after it, as 'The Big Dog'.
However, Canis Major does feature a pair of interacting galaxies. NGC 2207 and IC 2163 are a pair of face-on spiral galaxies located 125 million light-years from Earth. About 40 million years ago, the two galaxies had a close encounter and are now moving farther apart; nevertheless, the smaller IC 2163 will eventually be incorporated into NGC 2207. As the interaction continues, gas and dust will be perturbed, sparking extensive star formation in both galaxies.
NGC 2359 (Thor's Helmet or the Duck Nebula) is a relatively bright nebula in Canis Major, with an approximate magnitude of 10, which is 10,000 light-years from Earth. The nebula is shaped by HD 56925, an unstable Wolf-Rayet star embedded within it.
In early classical Europe, Canis Major represented the dog Laelaps, a gift from Zeus to Europa; or sometimes the hound of Procris, Diana's nymph; or the one given by Aurora to Cephalus, so famed for its speed that Zeus elevated it to the sky. 
It was also considered to represent one of Orion's hunting dogs, pursuing Lepus the Hare or helping Orion fight Taurus the Bull; and is referred to in this way by Aratos, Homer and Hesiod. The ancient Greeks refer only to one dog, but by Roman times, Canis Minor appears as Orion's second dog. 
Sirius was considered a dog in its own right; early Greek mythology sometimes tells that the constellation represents a two-headed dog. As such, together with the area of the sky that is deserted (now considered as the new and extremely faint constellations Camelopardalis and Lynx), and the other features of the area in the Zodiac sign of Gemini (i.e. the Milky Way, and the constellations Gemini, Orion, Auriga, and Canis Minor), this may be the origin of the myth of the cattle of Geryon, which forms one of The Twelve Labours of Heracles.[original research?]
Both the Maori people and the people of the Tuamotus recognized the figure of Canis Major as a distinct entity, though it was sometimes absorbed into other constellations. Te Huinga-o-Rehua, also called Te Putahi-nui-o-Rehua and Te Kahui-Takurua, ("The Assembly of Rehua" or "The Assembly of Sirius") was a Maori constellation that included both Canis Minor and Canis Major, along with some surrounding stars. Related was Taumata-o-Rehua, also called Pukawanui, the Mirror of Rehua, formed from an undefined group of stars in Canis Major. They called Sirius Rehua and Takarua, corresponding to two of the names for the constellation, though Rehua was a name applied to other stars in various Maori groups and other Polynesian cosmologies. The Tuamotu people called Canis Major Muihanga-hetika-o-Takurua, "the abiding assemblage of Takurua". In their cosmology, Sirius had various names, including Takurua-te-upuupu, Te Kaha ("coconut fiber"), Te Upuupu, Taranga, and Vero-ma-torutoru ("flaming and diminishing"). Beta Canis Majoris was called Oupo. Sirius itself was named by several other Polynesian cultures. The Hawaiian people had many names for Sirius, including Aa ("glowing"), Hoku-kauopae, Kau-ano-meha (also Kaulanomeha), "Standing-alone-and-sacred", Hiki-kauelia or Hiki-kauilia (the navigational name), Hiki-kau-lono-meha ("star of solitary Lono", the astrological name), Kaulua (also Kaulua-ihai-mohai, "flower of the heavens"), Hiki-kauelia, Hoku-hoo-kele-waa ("star which causes the canoe to sail", a marine navigation name), and Kaulua-lena ("yellow star"). The people of the Society Islands called Sirius variously Taurua-fau-papa, Taurua-nui-te-amo-aha, and Taurua-e-hiti-i-tara-te-feiai. Other names for Sirius included Palolo-mua (Futuna), Mere (Mangaia), Apura (Manihiki), Taku-ua (Marquesas Islands), and Tokiva (Pukapuka).
The Space probe Voyager 2 is slowly moving in the direction of this constellation, though it will not be nearing any of the stars in this constellation for many thousands of years, by which time its batteries will be exhausted.
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|Wikimedia Commons has media related to Canis Major.|
- The Deep Photographic Guide to the Constellations: Canis Major
- Star Tales – Canis Major
- Canis Major at Constellation Guide