Epsilon Canis Majoris is a

binary star A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in wh ...

system and the second-brightest object in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

Canis Major Canis Major is a constellation in the Southern Celestial Hemisphere, southern celestial hemisphere. In the second century, it was included in Ptolemy's 48 constellations, and is counted among the 88 modern constellations. Its name is Latin fo ...

. Its name is a

Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek or Latin letter followed by the genitive form of its parent constellation's Latin name. The original list of Bayer designations contained 1,564 stars. ...

that is Latinised from ε Canis Majoris, and abbreviated Epsilon CMa or ε CMa. This is the 22nd-

brightest star ''Brightest Star'' is the debut mini-album from J-pop vocal group Bright. This was their first CD released under major label Rhythm Zone (RZN) is a record label in the Avex Group that releases urban contemporary Japanese music. History Th ...

in the night sky with an apparent magnitude of 1.50. About 4.7 million years ago, it was the brightest star in the night sky, with an apparent magnitude of −3.99. Based upon

parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby objects ...

measurements obtained during the

Hipparcos ''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial obj ...

mission, it is about 430

light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s distant from the Sun. The two components are designated ε Canis Majoris A, officially named Adhara – the traditional name of the system, and B.

Nomenclature

''ε Canis Majoris'' (Latinised to ''Epsilon Canis Majoris'') is the binary system's

. The designations of the two components as ''ε Canis Majoris A'' and ''B'' derive from the convention used by the Washington Multiplicity Catalog (WMC) for

multiple star system A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. A large group of stars bound by gravitation is generally called a '' star cluster'' or '' galaxy'', although, broadly speaki ...

s, and adopted by the International Astronomical Union (IAU). ε Canis Majoris bore the traditional name ''Adhara'' (sometimes spelled ''Adara'', ''Adard'', ''Udara'' or ''Udra''), derived from the Arabic word عذارى 'aðāra', "virgins". In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire

star systems A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. A large group of stars bound by gravitation is generally called a ''star cluster'' or ''galaxy'', although, broadly speaking, ...

. It approved the name ''Adhara'' for the star ε Canis Majoris A on 21 August 2016 and it is now so included in the List of IAU-approved Star Names. In the 17th-century catalogue of stars in the ''Calendarium'' of Al Achsasi al Mouakket, this star was designated ''Aoul al Adzari'' (أول العذاري ''awwal al-adhara''), which was translated into Latin as ''Prima Virginum'', meaning ''First of the Virgins''. Along with δ Canis Majoris (Wezen), η Canis Majoris (Aludra) and ο² Canis Majoris (Thanih al Adzari), these stars were ''Al ʽAdhārā'' (''العذاري''), 'the Virgins'. In

Chinese Chinese can refer to: * Something related to China * Chinese people, people of Chinese nationality, citizenship, and/or ethnicity **''Zhonghua minzu'', the supra-ethnic concept of the Chinese nation ** List of ethnic groups in China, people of va ...

, (), meaning ''

Bow and Arrow The bow and arrow is a ranged weapon system consisting of an elastic launching device (bow) and long-shafted projectiles ( arrows). Humans used bows and arrows for hunting and aggression long before recorded history, and the practice was comm ...

'', refers to an asterism consisting of ε Canis Majoris, δ Canis Majoris, η Canis Majoris, κ Canis Majoris, ο Puppis, π Puppis, χ Puppis,

c Puppis The Bayer designations c Puppis and C Puppis are distinct and refer to two different stars in the constellation Puppis Puppis is a constellation in the southern sky. Puppis, the Latin translation of "poop deck", was originally part of an over-la ...

and

k Puppis k Puppis (k Pup, k Puppis) is a Bayer designation given to an optical double star in the constellation Puppis, the two components being k1 Puppis and k2 Puppis. Bayer designation Note that the Bayer designation for this star is "k" n ...

. Consequently, ε Canis Majoris itself is known as (, en, the Seventh Star of Bow and Arrow).

Physical properties

ε Canis Majoris is a binary star. The primary, ε Canis Majoris A, has an apparent magnitude of +1.5 and belongs to the

spectral classification In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

B2. Its color is blue or blueish-white, due to the surface temperature of 22,200 K. It emits a total radiation equal to 38,700 times that of the Sun. This star is the brightest source of extreme ultraviolet in the night sky. It is the strongest source of photons capable of ionizing hydrogen atoms in interstellar gas near the Sun, and is very important in determining the ionization state of the

Local Interstellar Cloud The Local Interstellar Cloud (LIC), also known as the Local Fluff, is an interstellar cloud roughly across, through which the Solar System is moving. This feature overlaps a region around the Sun referred to as the solar neighborhood. It is unk ...

. The +7.5-magnitude (the absolute magnitude amounts to +1.9) companion star, ε Canis Majoris B, is 7.5" away with a position angle of 161° of the main star. Despite the relatively large angular distance the components can only be resolved in large telescopes, since the primary is approximately 250 times brighter than its companion. A few million years ago, ε Canis Majoris was much closer to the Sun than it is at present, causing it to be a much brighter star in the night sky. About 4.7 million years ago, Adhara was 34 light-years from the Sun, and was the brightest star in the sky with a magnitude of –3.99. No other star has attained this brightness since, nor will any other star attain this brightness for at least five million years.

In culture

USS ''Adhara'' (AK-71) was a U.S. Navy ''Crater''-class cargo ship named after the star. ε Canis Majoris appears on the national flag of Brazil, symbolising the state of Tocantins.

References

{{DEFAULTSORT:Epsilon Canis Majoris B-type bright giants Binary stars Canis Major Canis Majoris, Epsilon 2618 CD-28 03666 Canis Majoris, 21 052089 033579 Adhara