Eta Ursae Majoris ( Latinised from η Ursae Majoris, abbreviated Eta UMa, η UMa), formally named Alkaid , is a

star A star is an astronomical object comprising a luminous spheroid of plasma held together by its gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night, but their immense distances from Earth ma ...

in the constellation of

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 ...

. It is the most eastern (leftmost) star in the

Big Dipper The Big Dipper ( US, Canada) or the Plough ( UK, Ireland) is a large asterism consisting of seven bright stars of the constellation Ursa Major; six of them are of second magnitude and one, Megrez (δ), of third magnitude. Four define a "bowl ...

(or Plough) asterism. However, unlike most stars of the Big Dipper, it is not a member of the Ursa Major moving group. With an

apparent visual magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...

of +1.84, it is the third-brightest star in the constellation and one of the

brightest stars This is a list of stars arranged by their apparent magnitude – their brightness as observed from Earth. It includes all stars brighter than magnitude +2.50 in visible light, measured using a ''V''-band filter in the UBV photometric system. 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 ...

Physical properties

Eta Ursae Majoris is a 10-million-year-old

B-type main sequence star A B-type main-sequence star (B V) is a main-sequence (hydrogen-burning) star of spectral type B and luminosity class V. These stars have from 2 to 16 times the mass of the Sun and surface temperatures between 10,000 and 30,000 K. B-type stars ...

with a

stellar 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 th ...

of B3 V. 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. 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 center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

. 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 A B-type main-sequence star (B V) is a main-sequence (hydrogen-burning) star of spectral type B and luminosity class V. These stars have from 2 to 16 times the mass of the Sun and surface temperatures between 10,000 and 30,000 K. B-type stars ...

. This star is an

X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30 ...

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 A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to identi ...

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. Eta Ursae Majoris 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 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. T ...

. 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 the grave.''The American Heritage Dictionary of the English Language'' (American Heritage Publishing Co., Inc., New York, ...

" ( '). 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 ...

, and

Alioth Epsilon Ursae Majoris is a star in the northern constellation of Ursa Major. The designation is Latinised from ε Ursae Majoris and abbreviated Epsilon UMa or ε UMa. It is officially named Alioth . Despite being designat ...

; while the four stars of the bowl,

Megrez Delta Ursae Majoris (δ Ursae Majoris, abbreviated Delta UMa, δ UMa), formally named Megrez , is a star in the northern constellation of Ursa Major. With an apparent magnitude of +3.3, it is the dimmest of the seven stars ...

, Phecda, Merak, and Dubhe, are the bier. 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, outreach ...

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 ''Alkaid'' for this star. 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 (; ) are people who religiously adhere to Hinduism.Jeffery D. Long (2007), A Vision for Hinduism, IB Tauris, , pages 35–37 Historically, the term has also been used as a geographical, cultural, and later religious identifier for ...

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

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...

and

Korea Korea ( ko, 한국, or , ) is a peninsular region in East Asia. Since 1945, it has been divided at or near the 38th parallel, with North Korea (Democratic People's Republic of Korea) comprising its northern half and South Korea (Republic of ...

, 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 maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage of ...

Crater class cargo ship The ''Crater''-class cargo ship were converted EC2-S-C1 type, Liberty cargo ships, constructed by the United States Maritime Commission (USMC) for use by the US Navy during World War II. The designation 'EC2-S-C1': 'EC' for Emergency Cargo, '2' fo ...

named after the star.

References

External links

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

Physical properties

Nomenclature

In culture

See also

References

External links