Alkaid , also called Eta Ursae Majoris ( Latinised from η Ursae Majoris, abbreviated Eta UMa, η UMa), is a

star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

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 ...

Ursa Major Ursa Major, also known as the Great Bear, is a constellation in the Northern Sky, whose associated mythology likely dates back into prehistory. Its Latin name means "greater (or larger) bear", referring to and contrasting it with nearby Ursa M ...

. It is the easternmost star in the

Big Dipper The Big Dipper (American English, US, Canadian English, Canada) or the Plough (British English, UK, Hiberno-English, Ireland) is an asterism (astronomy), asterism consisting of seven bright stars of the constellation Ursa Major; six of them ar ...

(or Plough) asterism. However, unlike most stars of the Big Dipper, it is not a member of the

Ursa Major moving group The Ursa Major Moving Group, also known as Collinder 285 and the Ursa Major association, is the closest Stellar kinematics#Moving groups, stellar moving group – a set of stars with common velocities in space and thought to have a common orig ...

. With an

apparent visual magnitude Apparent magnitude () is a measure of the 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 of the object's light ca ...

of +1.86, it is the third-brightest star in the constellation and one of the brightest stars 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 ...

Physical properties

Alkaid is a 10-million-year-old B-type main sequence star with a

stellar classification 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 B3 V. Since 1943, the

spectrum A spectrum (: spectra or spectrums) is a set of related ideas, objects, or properties whose features overlap such that they blend to form a continuum. The word ''spectrum'' was first used scientifically in optics to describe the rainbow of co ...

of this star has served as one of the stable anchor points by which other stars are classified. It has six times the mass; 3.4 times the radius, and is radiating around 594 times as much energy as the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

. Its outer atmosphere has an

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

of about 15,540 K, giving it the blue-white hue of a

B-type star 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 ...

. This star is an

X-ray An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...

emitter with a luminosity of . Eta Ursae Majoris was listed as a standard star for the spectral type B3 V. It has broadened

absorption line Absorption spectroscopy is spectroscopy that involves techniques that measure the absorption (electromagnetic radiation), absorption of electromagnetic radiation, as a function of frequency or wavelength, due to its interaction with a sample. Th ...

s due to its rapid rotation, which is common in stars of this type. However, the lines are very slightly distorted and variable, which may be caused by some emission from a weak disk of material produced by the rapid rotation. Alkaid is a relatively nearby and bright star and has been examined closely, but no exoplanets or companion stars have been discovered.

Nomenclature

''η Ursae Majoris'' (Latinised to ''Eta Ursae Majoris'') is the star'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

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 ...

has formally chosen the proper name ''Alkaid'' for this star. It bore the traditional names ''Alkaid'' (or ''Elkeid'' from the Arabic القايد القائد) and ''Benetnasch'' . ''Alkaid'' derives from the Arabic phrase meaning "The leader of the daughters of the

bier A bier is a stand on which a corpse, coffin, or casket containing a corpse is placed to lie in state or to be carried to its final disposition.''The American Heritage Dictionary of the English Language'' (American Heritage Publishing Co., In ...

" ( '). The daughters of the bier, i.e. the mourning maidens, are the three stars of the handle of the Big Dipper, Alkaid,

Mizar Mizar is a second-magnitude star in the handle of the Big Dipper asterism in the constellation of Ursa Major. It has the Bayer designation ζ Ursae Majoris ( Latinised as Zeta Ursae Majoris). It forms a well-known naked eye d ...

, and Alioth; while the four stars of the bowl, Megrez, Phecda, Merak, and

Dubhe Dubhe is a multiple star system in the northern constellation of Ursa Major. It is formally designated Alpha Ursae Majoris, Latinised from α Ursae Majoris, Despite being designated "α" (alpha), it is the second-brightest object ...

, are the bier. It is known as ''Běidǒuqī'' (北斗七 - the Seventh Star of the Northern Dipper) or ''Yáoguāng'' (瑤光 - the Star of Twinkling Brilliance) in Chinese. The

Hindu Hindus (; ; also known as Sanātanīs) are people who religiously adhere to Hinduism, also known by its endonym Sanātana Dharma. Jeffery D. Long (2007), A Vision for Hinduism, IB Tauris, , pp. 35–37 Historically, the term has also be ...

s knew this star as '' Marīci'', one of the Seven Rishis. In

Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

and

Korea Korea is a peninsular region in East Asia consisting of the Korean Peninsula, Jeju Island, and smaller islands. Since the end of World War II in 1945, it has been politically Division of Korea, divided at or near the 38th parallel north, 3 ...

, Alkaid is known as ''Hagunsei'' and ''Mukokseong'' respectively ("the military breaking star" or "most corner star"). Both meanings come from ancient China's influence in both countries.

In culture

USS Alkaid (AK-114) was a

United States Navy The United States Navy (USN) is the naval warfare, maritime military branch, service branch of the United States Department of Defense. It is the world's most powerful navy with the largest Displacement (ship), displacement, at 4.5 millio ...

Crater class cargo ship named after the star. Alkaid is one of the Behenian fixed stars, used in

Alchemy Alchemy (from the Arabic word , ) is an ancient branch of natural philosophy, a philosophical and protoscientific tradition that was historically practised in China, India, the Muslim world, and Europe. In its Western form, alchemy is first ...

. The fossil starfish '' Alkaidia'' is named after Alkaid.

References

External links

Alkaid
at Jim Kaler's ''Stars'' website {{Portal bar, Astronomy, Stars, Outer space Ursae Majoris, Eta Big Dipper B-type main-sequence stars Ursa Major Alkaid Ursae Majoris, 85 5191 120315 067301 BD+50 2027