Canis Major

Coordinates: Sky map 07h 00m 00s, −20° 00′ 00″
Source: Wikipedia, the free encyclopedia.
"CMa" and "Great Dog" redirect here. For other uses, see CMA (disambiguation) and Great Dog (disambiguation).

Canis Major
Constellation
43rd)
Main stars8
Bayer/Flamsteed
stars		32
Stars with planets7
Stars brighter than 3.00m5
Stars within 10.00 pc (32.62 ly)1
Brightest starSirius (α CMa) (−1.46m)
Messier objects1
Meteor showers0
Bordering
constellations
Visible at latitudes between +60° and −90°.
Best visible at 21:00 (9 p.m.) during the month of February.

Canis Major is a

88 modern constellations. Its name is Latin for "greater dog" in contrast to Canis Minor, the "lesser dog"; both figures are commonly represented as following the constellation of Orion the hunter through the sky. The Milky Way passes through Canis Major and several open clusters lie within its borders, most notably M41
.

Canis Major contains

RX J0720.4-3125
has a radius of a mere 5 km.

History and mythology

In western astronomy

In ancient

Ishtar, daughter of Enlil.[2] Ninurta was linked to the later deity Marduk, who was said to have slain the ocean goddess Tiamat with a great bow, and worshipped as the principal deity in Babylon.[3] The Ancient Greeks replaced the bow and arrow depiction with that of a dog.[4]

Sirius A
, the brightest star in the night sky, lies in Canis Major.

In Greek Mythology, Canis Major represented the dog

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.[5] It was also considered to represent one of Orion's hunting dogs,[6] 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. Alternative names include Canis Sequens and Canis Alter.[5] Canis Syrius was the name used in the 1521 Alfonsine tables.[5]

The Roman myth refers to Canis Major as Custos Europae, the dog guarding Europa but failing to prevent her abduction by

Abū Rayḥān al-Bīrūnī referred to Orion as Kalb al-Jabbār, "the Dog of the Giant".[5] Among the Merazig of Tunisia, shepherds note six constellations that mark the passage of the dry, hot season. One of them, called Merzem, includes the stars of Canis Major and Canis Minor and is the herald of two weeks of hot weather.[8]

Canis Major as depicted on the Manuchihr Globe made in Mashhad 1632–33 AD. Adilnor Collection, Sweden.

In non-western astronomy

Canis Major, observed above Kuantan (north is towards top right)

In

Canis Major is located in the Vermilion Bird (南方朱雀; Nán Fāng Zhū Què), where the stars were classified in several separate asterisms of stars. The Military Market (軍市; Jūnshì) was a circular pattern of stars containing Nu3, Beta, Xi1 and Xi2, and some stars from Lepus.[9] The Wild Cockerel (野雞; Yějī) was at the centre of the Military Market, although it is uncertain which stars depicted what. Schlegel reported that the stars Omicron and Pi Canis Majoris might have been them,[10] while Beta or Nu2 have also been proposed.[11] Sirius was Tiānláng (天狼), the Celestial Wolf,[12] denoting invasion and plunder.[11] Southeast of the Wolf was the asterism Húshǐ (弧矢), the celestial Bow and Arrow, which was interpreted as containing Delta, Epsilon, Eta and Kappa Canis Majoris and Delta Velorum. Alternatively, the arrow was depicted by Omicron2 and Eta and aiming at Sirius (the Wolf), while the bow comprised Kappa, Epsilon, Sigma, Delta and 164 Canis Majoris, and Pi and Omicron Puppis.[13]

Both the Māori 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 Māori constellation that included both Canis Minor and Canis Major, along with some surrounding stars.[14][15] Related was Taumata-o-Rehua, also called Pukawanui, the Mirror of Rehua, formed from an undefined group of stars in Canis Major.[16][17] 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 Māori groups and other Polynesian cosmologies.[18][19] The Tuamotu people called Canis Major Muihanga-hetika-o-Takurua, "the abiding assemblage of Takarua".[20]

The Tharumba people of the

native cat") sought to lure the further wife (Epsilon) away, but Unurgunite assaulted him and he has been wandering the sky ever since.[24]

Characteristics

Canis Major is a constellation in the

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".[25] The official constellation boundaries, as set by Belgian astronomer Eugène Delporte in 1930, are defined by a quadrilateral; 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°.[1] Covering 380 square degrees or 0.921% of the sky, it ranks 43rd of the 88 currently-recognized constellations in size.[26]

Features

The stars of Canis Major as they can be seen by the naked eye; lines have been added for clarity.

Stars

See also: List of stars in Canis Major

Canis Major is a prominent constellation because of its many bright stars. These include Sirius (Alpha Canis Majoris), the brightest star in the night sky, as well as three other stars above magnitude 2.0.[6] Furthermore, two other stars are thought to have previously outshone all others in the night sky—Adhara (Epsilon Canis Majoris) shone at −3.99 around 4.7 million years ago, and Mirzam (Beta Canis Majoris) peaked at −3.65 around 4.42 million years ago. Another, NR Canis Majoris, will be brightest at magnitude −0.88 in about 2.87 million years' time.[27]

The German cartographer

Nicolas Louis de Lacaille added lettered stars a to k (though none are in use today).[29] John Flamsteed numbered 31 stars, with 3 Canis Majoris being placed by Lacaille into Columba as Delta Columbae (Flamsteed had not recognised Columba as a distinct constellation).[30] He also labelled two stars—his 10 and 13 Canis Majoris—as Kappa1 and Kappa2 respectively, but subsequent cartographers such as Francis Baily and John Bevis dropped the fainter former star, leaving Kappa2 as the sole Kappa.[28] Flamsteed's listing of Nu1, Nu2, Nu3, Xi1, Xi2, Omicron1 and Omicron2 have all remained in use.[31]

Canis Major as depicted in Urania's Mirror, a set of constellation cards published in London c.1825. Next to it are Lepus and Columba (partly cut off).

Sirius is the

ancient Egyptian calendar.[6] The star marked the Great Dog's mouth on Bayer's star atlas.[33]

Flanking Sirius are Beta and

supergiant star of spectral type B3Ib, around 46,000 times as luminous as the sun and, at 2500 light-years distant, 300 times further away than Sirius.[37]

Epsilon, Omicron2, Delta, and Eta Canis Majoris were called Al Adzari "the virgins" in medieval Arabic tradition.[38] Marking the dog's right thigh on Bayer's atlas is Epsilon Canis Majoris,[33] also known as Adhara. At magnitude 1.5, it is the second-brightest star in Canis Major and the 23rd-brightest star in the sky. It is a blue-white supergiant of spectral type B2Iab, around 404 light-years from Earth.[39] This star is one of the brightest known extreme ultraviolet sources in the sky.[40] It is a binary star; the secondary is of magnitude 7.4. Its traditional name means "the virgins", having been transferred from the group of stars to Epsilon alone.[41] Nearby is Delta Canis Majoris, also called Wezen. It is a yellow-white supergiant of spectral type F8Iab and magnitude 1.84, around 1605 light-years from Earth.[42] With a traditional name meaning "the weight", Wezen is 17 times as massive and 50,000 times as luminous as the Sun. If located in the centre of the Solar System, it would extend out to Earth as its diameter is 200 times that of the Sun. Only around 10 million years old, Wezen has stopped fusing hydrogen in its core. Its outer envelope is beginning to expand and cool, and in the next 100,000 years it will become a red supergiant as its core fuses heavier and heavier elements. Once it has a core of iron, it will collapse and explode as a supernova.[43] Nestled between Adhara and Wezen lies Sigma Canis Majoris, known as Unurgunite to the Boorong and Wotjobaluk people,[23] a red supergiant of spectral type K7Ib that varies irregularly between magnitudes 3.43 and 3.51.[44]

Also called Aludra, Eta Canis Majoris is a blue-white supergiant of spectral type B5Ia with a luminosity 176,000 times and diameter around 80 times that of the Sun.

spectrum indicating a main star of spectral type B2.5V.[48]

Between these stars and Sirius lie Omicron1, Omicron2, and Pi Canis Majoris. Omicron2 is a massive supergiant star about 21 times as massive as the Sun.[49] Only 7 million years old,[49] it has exhausted the supply of hydrogen at its core and is now processing helium.[50] It is an Alpha Cygni variable that undergoes periodic non-radial pulsations, which cause its brightness to cycle from magnitude 2.93 to 3.08 over a 24.44-day interval.[51] Omicron1 is an orange K-type supergiant of spectral type K2.5Iab that is an irregular variable star, varying between apparent magnitudes 3.78 and 3.99.[52] Around 18 times as massive as the Sun, it shines with 65,000 times its luminosity.[53]

North of Sirius lie Theta and Mu Canis Majoris, Theta being the most northerly star with a Bayer designation in the constellation.[54] Around 8 billion years old, it is an orange giant of spectral type K4III that is around as massive as the Sun but has expanded to 30 times the Sun's diameter.[55] Mu is a multiple star system located around 1244 light-years distant,[56] its components discernible in a small telescope as a 5.3-magnitude yellow-hued and 7.1-magnitude bluish star.[57] The brighter star is a giant of spectral type K2III,[56] while the companion is a main sequence star of spectral type B9.5V.[58] Nu1 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.[6]

At the southern limits of the constellation lie Kappa and Lambda Canis Majoris. Although of similar spectra and nearby each other as viewed from Earth, they are unrelated.[26] Kappa is a Gamma Cassiopeiae variable of spectral type B2Vne,[59] which brightened by 50% between 1963 and 1978, from magnitude 3.96 or so to 3.52.[60] It is around 659 light-years distant.[61] Lambda is a blue-white B-type main sequence dwarf with an apparent magnitude of 4.48 located around 423 light-years from Earth.[62] It is 3.7 times as wide as and 5.5 times as massive as the Sun, and shines with 940 times its luminosity.[54]

Very Large Telescope image of the surroundings of VY Canis Majoris

Canis Major is also home to many variable stars.

accretion disc.[69]

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;[6] its components are two massive hot blue stars, one a blue supergiant of spectral type O7.5–8 Iab, while its companion is a slightly cooler, less evolved and less luminous supergiant of spectral type O9.7Ib. The stars are 200,000 and 63,000 times as luminous as the Sun. However the fainter star is the more massive at 19 solar masses to the primary's 16.[73] R Canis Majoris is another eclipsing binary that varies from magnitude 5.7 to 6.34 over 1.13 days,[74] with a third star orbiting these two every 93 years. The shortness of the orbital period and the low ratio between the two main components make this an unusual Algol-type system.[75]

Seven star systems have been found to have planets. Nu2 Canis Majoris is an ageing orange giant of spectral type K1III of apparent magnitude 3.91 located around 64 light-years distant.[76] Around 1.5 times as massive and 11 times as luminous as the Sun, it is orbited over a period of 763 days by a planet 2.6 times as massive as Jupiter.[77] HD 47536 is likewise an ageing orange giant found to have a planetary system—echoing the fate of the Solar System in a few billion years as the Sun ages and becomes a giant.[78] Conversely, HD 45364 is a star 107 light-years distant that is a little smaller and cooler than the Sun, of spectral type G8V, which has two planets discovered in 2008. With orbital periods of 228 and 342 days, the planets have a 3:2 orbital resonance, which helps stabilise the system.[79] HD 47186 is another sunlike star with two planets; the inner—HD 47186 b—takes four days to complete an orbit and has been classified as a Hot Neptune, while the outer—HD 47186 c—has an eccentric 3.7-year period orbit and has a similar mass to Saturn.[80] HD 43197 is a sunlike star around 183 light-years distant that has two planets: a hot Jupiter-size planet with an eccentric orbit. The other planet, HD 43197 c, is another massive Jovian planet with a slightly oblong orbit outside of its habitable zone. [81]

Z Canis Majoris is a star system a mere 300,000 years old composed of two pre-main-sequence stars—a FU Orionis star and a Herbig Ae/Be star,[82] which has brightened episodically by two magnitudes to magnitude 8 in 1987, 2000, 2004 and 2008.[83] The more massive Herbig Ae/Be star is enveloped in an irregular roughly spherical cocoon of dust that has an inner diameter of 20 AU (3.0×109 km) and outer diameter of 50 AU (7.5×109 km). The cocoon has a hole in it through which light shines that covers an angle of 5 to 10 degrees of its circumference. Both stars are surrounded by a large envelope of in-falling material left over from the original cloud that formed the system. Both stars are emitting jets of material, that of the Herbig Ae/Be star being much larger—11.7 light-years long.[84] Meanwhile, FS Canis Majoris is another star with infra-red emissions indicating a compact shell of dust, but it appears to be a main-sequence star that has absorbed material from a companion. These stars are thought to be significant contributors to interstellar dust.[85]

Deep-sky objects

The band of the

HD 56925, an unstable Wolf–Rayet star embedded within it.[92]

ESO 489-056 is an irregular dwarf galaxy, located 16 million light-years distant.[93]

In 2003, an overdensity of stars in the region was announced to be the

Milky Way's halo and thick disk populations rather than a separate dwarf spheroidal galaxy.[94] On the other hand, a globular cluster in Puppis, NGC 2298—which appears to be part of the Canis Major dwarf system—is extremely metal-poor, suggesting it did not arise from the Milky Way's thick disk, and instead is of extragalactic origin.[95]

low-surface-brightness galaxy that has one of the lowest metallicities known.[101]

References

Citations

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Bibliography

External links

Wikimedia Commons has media related to Canis Major.
Wikisource has the text of the 1911 Encyclopædia Britannica article "Canis Major".
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