Alpha Ursae Majoris, Latinised from α Ursae Majoris, formally named Dubhe , is, despite being designated "α" ( alpha), the second-brightest object in the northern 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 ...

. This prominent asterism is known as 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 ...

, the Plough, and the Great Bear. Alpha Ursae Majoris is the northern of the 'pointers' (or 'guards'), the second being Beta Ursae Majoris, or 'Merak' – this pair of stars point towards

Polaris Polaris is a star in the northern circumpolar constellation of Ursa Minor. It is designated α Ursae Minoris ( Latinized to ''Alpha Ursae Minoris'') and is commonly called the North Star or Pole Star. With an apparent magnitude that ...

, the North Star.

Stellar system

α Ursae Majoris is located at a distance of approximately 123

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 from the Sun, based on

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 object ...

measurements. It is a spectroscopic binary made up of the stars designated ''α Ursae Majoris A'' and ''α Ursae Majoris B''. The pair orbit at a separation of about 23

astronomical unit The astronomical unit (symbol: au, or or AU) is a unit of length, roughly the distance from Earth to the Sun and approximately equal to or 8.3 light-minutes. The actual distance from Earth to the Sun varies by about 3% as Earth orbi ...

s (AU) with a period of 44.5 years and an

eccentricity Eccentricity or eccentric may refer to: * Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal" Mathematics, science and technology Mathematics * Off- center, in geometry * Eccentricity (graph theory) of a ...

(ovalness) of 0.44. There is another spectroscopic binary at an

angular separation Angular distance \theta (also known as angular separation, apparent distance, or apparent separation) is the angle between the two sightlines, or between two point objects as viewed from an observer. Angular distance appears in mathematics (in pa ...

of 7.1 arcminutes, forming a 7th magnitude pair showing an F8 spectral type with an orbital period of 6.035 days and an eccentricity of 0.09. It is sometimes referred to as Alpha Ursae Majoris C, but is separately catalogued as HD 95638. Together they form a quadruple star system. Component A is the system's primary, and it is a

giant star A giant star is a star with substantially larger radius and luminosity than a main-sequence (or ''dwarf'') star of the same surface temperature.Giant star, entry in ''Astronomy Encyclopedia'', ed. Patrick Moore, New York: Oxford University Press ...

that has

evolved Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation te ...

away from the

main sequence In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Her ...

after consuming the hydrogen at its core. It is 280 million years old with 3.4 times the mass and has expanded 17 times the radius of the Sun. The star is radiating 165 times the luminosity of the Sun from its enlarged

photosphere The photosphere is a star's outer shell from which light is radiated. The term itself is derived from Ancient Greek roots, φῶς, φωτός/''phos, photos'' meaning "light" and σφαῖρα/''sphaira'' meaning "sphere", in reference to it ...

at 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 5,012 K. The secondary star, component B, is a

star that has 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 t ...

of F0V. α Ursae Majoris has been reported to vary in brightness by about a thousandth of a magnitude. Ten radial oscillation modes have been detected, with periods between 6.4 hours and 6.4 days. Although it is part of the constellation of Ursa Major, it is not part of the Ursa Major Moving Group of stars that have a common motion through space.

Nomenclature

''α Ursae Majoris'' (Latinised to ''Alpha Ursae Majoris'') is the star system'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 name ''Dubhe'', which is derived 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; Walte ...

for 'bear', , from the phrase ' 'the back of the Greater Bear'. The ancient Egyptians called it ''Ak'', meaning 'The Eye'. 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 List of proper names of stars, proper names for stars for the international astronomical community. It operates under ...

(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 ''Dubhe'' for the star α Ursae Majoris A. The Hindus refer to the star as ''

Kratu Kratu ( sa, क्रतु, lit=strength) is described as one of the manasaputras, the mind-born children of the creator deity, Brahma, in Hinduism. He is also a rishi, who appears in two different ages. He is considered to be one among the s ...

'', one of the Seven Rishis. In Chinese, Běi Dǒu, meaning '' Northern Dipper'', refers to an asterism equivalent to the Big Dipper. Consequently, the

Chinese name Chinese names or Chinese personal names are names used by individuals from Greater China and other parts of the Chinese-speaking world throughout East and Southeast Asia (ESEA). In addition, many names used in Japan, Korea and Vietnam are oft ...

for Alpha Ursae Majoris itself is Běi Dǒu yī, ( en, the First Star of Northern Dipper) and Tiān Shū, ( en, Star of Celestial Pivot).

In culture

Dubhe is the official star of the

State of Utah Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to its w ...

. ''Dubhe'' was a ship in the

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 ...

. The Danish National Home Guard Navy ship

MHV806 This is a list of the active vessels of the Royal Danish Navy. Overview 1st Squadron Division 11 * ''Thetis''-class ocean patrol vessels: ** ''HDMS Thetis'' (F357) ** ''HDMS Triton'' (F358) ** ''HDMS Vædderen''(F359) ** ''HDMS Hvidbjør ...

is also named'' Dubhe''.

References

{{Portal bar, Astronomy, Stars, Spaceflight, Outer space, Solar System K-type giants F-type main-sequence stars Suspected variables 4 Double stars Big Dipper Ursa Major (constellation) Ursae Majoris, Alpha BD+62 1161 Ursae Majoris, 50 095689 054061 4301 Dubhe

Stellar system

Nomenclature

In culture

See also

References