Eta Canis Majoris (η Canis Majoris, abbreviated Eta CMa, η CMa), also named Aludra , is a

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

in the

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

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 ...

. Since 1943, the

spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors ...

of this star has served as one of the stable anchor points by which other stars are classified.

Nomenclature

''η Canis Majoris'' ( Latinised to ''Eta Canis Majoris'') is the star's

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 ...

. The traditional name ''Aludra'' originates from the

Arabic Arabic (, ' ; , ' or ) is a Semitic language spoken primarily across the Arab world.Semitic languages: an international handbook / edited by Stefan Weninger; in collaboration with Geoffrey Khan, Michael P. Streck, Janet C. E.Watson; Walter ...

: ''العذراء'' ''al-adhraa'', 'the virgin'. This star, along with Epsilon Canis Majoris (Adhara), Delta Canis Majoris (Wezen) and Omicron² Canis Majoris (Thanih al Adzari), were ''Al 'Adhārā'' (''العذاري''), 'the Virgins'. In 2016, the

International Astronomical Union The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...

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 catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN; which included ''Aludra'' for this star. In Chinese, (), 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 common ...

'', refers to an asterism consisting of Eta Canis Majoris, Delta Canis Majoris,

HD 63032 c Puppis, also known as HD 63032 and HR 3017, is a spectroscopic binary star in the constellation Puppis. Its apparent magnitude is 3.61. Located around distant, the primary is an orange-red bright giant or supergiant of spectral type K2. ...

HD 65456 χ Puppis, Latinised as Chi Puppis, is a single star in the southern constellation of Puppis. It has a white hue and is faintly visible to the eye at night with an apparent visual magnitude of 4.79. The star is located at a distance of ...

Omicron Puppis Omicron Puppis (ο Puppis) is candidate binary star system in the southern constellation of Puppis. It is visible to the naked eye, having a combined apparent visual magnitude of +4.48. Based upon an annual parallax shift of 2.30&n ...

, k Puppis, Epsilon Canis Majoris,

Kappa Canis Majoris Kappa Canis Majoris, Latinized from κ Canis Majoris, is a solitary, blue-white hued star in the constellation Canis Major. It is visible to the naked eye with an apparent visual magnitude of +3.87. Based upon an annual parallax shift ...

and

Pi Puppis Pi Puppis, Latinized from π Puppis, also named Ahadi, is the second-brightest star in the southern constellation of Puppis. It has an apparent visual magnitude of 2.733, so it can be viewed with the naked eye at night. Paral ...

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

Properties

A blue-white supergiant, Eta CMa has been used as a standard for the

spectral type 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 ...

of B5Ia. Eta CMa shines brightly in the skies in spite of a large distance from

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's sur ...

due to being intrinsically many times brighter than the Sun. It has a luminosity over 100,000 times and a radius around 54 times that of the Sun. It has only been around a fraction of the time the Sun has, less than 10 million years, yet is already in the last stages of its life. It is still expanding and may become a red supergiant, or perhaps has already passed that phase, but in either case it will become a

supernova A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or whe ...

within the next few million years. Eta CMa is classified as an Alpha Cygni-type

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as e ...

and its brightness varies from magnitude +2.38 to +2.48 over a period of 4.7 days.

Namesakes

Both USS ''Aludra'' (AF-55), an ''Alstede''-class stores ship, and USS ''Aludra'' (AK-72), a ''Crater''-class cargo ship, were U.S. Navy vessels named after the star.

References

{{DEFAULTSORT:Eta Canis Majoris Alpha Cygni variables Canis Majoris, Eta B-type supergiants Canis Major Canis Majoris, 31 058350 035904 Aludra 2827 CD-29 04328