Epsilon Canis Majoris is a
binary star
A binary star or binary star system 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 as separate stars us ...
system and the second-brightest star 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 first constellati ...
of
Canis Major
Canis Major is a constellation in the 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 for "greater dog" in contrast to C ...
. Its name is a
Bayer designation
A Bayer designation is a stellar designation in which a specific star is identified by a Greek alphabet, Greek or Latin letter followed by the genitive case, genitive form of its parent constellation's Latin name. The original list of Bayer design ...
that is
Latinised from ε Canis Majoris, and abbreviated Epsilon CMa or ε CMa. This is the 22nd-
brightest star in the
night sky
The night sky is the nighttime appearance of celestial objects like stars, planets, and the Moon, which are visible in a clear sky between sunset and sunrise, when the Sun is below the horizon.
Natural light sources in a night sky include moonlig ...
with an
apparent magnitude
Apparent magnitude () is a measure of the Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...
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 sightline, lines of sight and is measured by the angle or half-angle of inclination between those two lines. Due to perspective (graphica ...
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 and distances of ...
and the Gaia
In Greek mythology, Gaia (; , a poetic form of ('), meaning 'land' or 'earth'),, , . also spelled Gaea (), is the personification of Earth. Gaia is the ancestral mother—sometimes parthenogenic—of all life. She is the mother of Uranus (S ...
mission, it is about light-year
A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...
s distant.
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 Bayer designation
A Bayer designation is a stellar designation in which a specific star is identified by a Greek alphabet, Greek or Latin letter followed by the genitive case, genitive form of its parent constellation's Latin name. The original list of Bayer design ...
. 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. It may sometimes be used to refer to a single star. A large group of stars bound by gravitation is generally called a ''st ...
s, and adopted by the International Astronomical Union
The International Astronomical Union (IAU; , UAI) is an international non-governmental organization (INGO) with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach, education, and developmen ...
(IAU).[
ε Canis Majoris bore the traditional name ''Adhara'' (sometimes spelled ''Adara'', ''Adard'', ''Udara'' or ''Udra''), derived from the ]Arabic
Arabic (, , or , ) is a Central Semitic languages, Central Semitic language of the Afroasiatic languages, Afroasiatic language family spoken primarily in the Arab world. The International Organization for Standardization (ISO) assigns lang ...
word عذارى 'aðāra', "virgins".[ In 2016, the ]International Astronomical Union
The International Astronomical Union (IAU; , UAI) is an international non-governmental organization (INGO) with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach, education, and developmen ...
organized a Working Group on Star Names
The International Astronomical Union (IAU) established a Working Group on Star Names (WGSN) in May 2016 to catalog and standardize proper names for stars for the international astronomical community. It operates under Division C – Education ...
(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. It may sometimes be used to refer to a single star. A large group of stars bound by gravitation is generally called a ''st ...
.[ 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
Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...
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, (), meaning '']Bow and Arrow
The bow and arrow is a ranged weapon system consisting of an elasticity (physics), elastic launching device (bow) and long-shafted projectiles (arrows). Humans used bows and arrows for hunting and aggression long before recorded history, and the ...
'', 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 and k Puppis. Consequently, ε Canis Majoris itself is known as (, ).[AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 17 日]
Physical properties
ε Canis Majoris is a binary star.[ The primary, ε Canis Majoris A, has an ]apparent magnitude
Apparent magnitude () is a measure of the Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...
of +1.5 and belongs to the spectral classification
''Spectral'' is a 2016 Hungarian-American military science fiction action film co-written and directed by Nic Mathieu. Written with Ian Fried & George Nolfi, the film stars James Badge Dale as DARPA research scientist Mark Clyne, with Max M ...
B2. Its color is blue or blueish-white, due to the surface temperature of . 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
Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...
atoms in interstellar gas near the Sun, and is very important in determining the ionization state of the Local Interstellar Cloud.[ Its ]rotation period
In astronomy, the rotation period or spin period of a celestial object (e.g., star, planet, moon, asteroid) has two definitions. The first one corresponds to the '' sidereal rotation period'' (or ''sidereal day''), i.e., the time that the objec ...
is estimated to be about 5 days.[
The exact evolutionary status of is uncertain. Spectroscopically it has been given the class B2 II,][ with the ]luminosity class
In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction gratin ...
of II indicating that is a bright giant
A giant star has a substantially larger radius and luminosity than a main-sequence (or ''dwarf'') star of the same surface temperature. They lie above the main sequence (luminosity class V in the Yerkes spectral classification) on the Hertzspr ...
, more luminous than a typical giant (luminosity class III). However, it appear less luminous than the expected for this luminosity class, and is more likely of class B2 III-II.[ Two studies suggest is still in the late ]main sequence
In astronomy, the main sequence is a classification of stars which appear on plots of stellar color index, color versus absolute magnitude, brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or d ...
( TAMS), rather than being a giant.[ One of these even suggested it could be the final product of a ]stellar merger
A stellar collision is the coming together of two stars caused by stellar dynamics within a star cluster, or by the orbital decay of a binary star due to stellar mass loss or gravitational radiation, or by other mechanisms not yet well understo ...
.[
The +7.5-magnitude (the absolute magnitude amounts to +1.9) companion star, ε Canis Majoris B, is away with a position angle of 161° of the main star. Despite the relatively large ]angular distance
Angular distance or angular separation is the measure of the angle between the orientation (geometry), orientation of two straight lines, ray (geometry), rays, or vector (geometry), vectors in three-dimensional space, or the central angle subtende ...
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 4.4 million years ago, Adhara was light-years from the Sun, and was the brightest star in the night sky with a magnitude of . 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
The national flag of Brazil is a blue disc depicting a starry sky (which includes the Crux, Southern Cross) spanned by a curved band inscribed with the List of national mottos, national motto ('Order and Progress'), within a yellow rhombus, on ...
, symbolising the state of Tocantins
Tocantins () is one of the 26 states of Brazil. It is the newest state, formed in 1988 and encompassing what had formerly been the northern two-fifths of the state of Goiás. Tocantins covers and had an estimated population of 1,496,880 in 2014 ...
.[
]
Notes
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