Alpha Cephei (α Cephei, abbreviated Alpha Cep, α Cep), officially named Alderamin , is a

second magnitude star 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 cau ...

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 ...

Cepheus Cepheus (Ancient Greek: Κηφεύς ''Kepheús'') may refer to: In Greek mythology * Cepheus (father of Andromeda), and King of Aethiopia * Cepheus (son of Aleus), a king of Tegea, Arcadia In astronomy * Cepheus (constellation), one of the 88 m ...

near the

northern pole Northern Pole (北极 in Simplified Chinese, ''běi jí'' in Pinyin) is a traditional Chinese asterism found in the Purple Forbidden enclosure (紫微垣 in Simplified Chinese, ''zǐ wēi yuán'' in Pinyin). It consists of five stars found in the ...

. The star is relatively close to

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

at 49

light year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distance, astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by t ...

s (''ly'') and drifting closer with a heliocentric

radial velocity The radial velocity or line-of-sight velocity of a target with respect to an observer is the rate of change of the vector displacement between the two points. It is formulated as the vector projection of the target-observer relative velocity ...

of about −16 km/s.

Nomenclature

''α Cephei'' ( Latinised to ''Alpha Cephei'') 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 ...

. It has a

Flamsteed designation A Flamsteed designation is a combination of a number and constellation name that uniquely identifies most naked eye stars in the 88 modern constellations, modern constellations visible from southern England. They are named after John Flamsteed, au ...

of 5 Cephei. It bore the traditional name ''Alderamin'', a contraction of 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 ...

phrase ''الذراع اليمين'' ''al-dhirā‘ al-yamīn'', meaning "the right arm". 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 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 ''Alderamin'' for this star.

Visibility

With a declination in excess of 62 degrees north, Alpha Cephei never rises south of −27° latitude, which means for much of South America, Australia, South Africa, and all of New Zealand, the star stays below the horizon. The star is circumpolar throughout all of

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

, northern Asia, Canada, and American cities as far south as

San Diego San Diego ( , ) is a city on the Pacific coast of Southern California, adjacent to the Mexico–United States border. With a population of over 1.4 million, it is the List of United States cities by population, eighth-most populous city in t ...

. Since Alpha Cephei has an apparent magnitude of about 2.5, the star is the brightest in the constellation and is easily observable to the naked eye, even in light-polluted cities.

Pole star

Alpha Cephei is located near the precessional path traced across the

celestial sphere In astronomy and navigation, the celestial sphere is an abstract sphere that has an arbitrarily large radius and is concentric to Earth. All objects in the sky can be conceived as being projected upon the inner surface of the celestial sphere, ...

by the Earth's

North pole The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is the point in the Northern Hemisphere where the Earth's rotation, Earth's axis of rotation meets its surface. It is called the True North Pole to distingu ...

. That means that it periodically comes within 3° of being a

pole star A pole star is a visible star that is approximately aligned with the axis of rotation of an astronomical body; that is, a star whose apparent position is close to one of the celestial poles. On Earth, a pole star would lie directly overhead when ...

, a title currently held by

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

. Alpha Cephei will next be the North Star in about the year 7500 AD. The north pole of

Mars Mars is the fourth planet from the Sun. It is also known as the "Red Planet", because of its orange-red appearance. Mars is a desert-like rocky planet with a tenuous carbon dioxide () atmosphere. At the average surface level the atmosph ...

points to the midpoint of the line connecting the star and

Deneb Deneb () is a blue supergiant star in the constellation of Cygnus. It is the brightest star in the constellation and the 19th brightest in the night sky, with an apparent magnitude slightly varying between +1.21 and +1.29. Deneb is one ...

Properties

Alderamin is a white class A star, evolving off the

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 ...

into a

subgiant A subgiant is a star that is brighter than a normal main-sequence star of the same spectral class, but not as bright as giant stars. The term subgiant is applied both to a particular spectral luminosity class and to a stage in the evolution ...

, probably on its way to becoming a

red giant A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses ()) in a late phase of stellar evolution. The stellar atmosphere, outer atmosphere is inflated and tenuous, making the radius large and the surface t ...

as its hydrogen supply runs low. On average, Alderamin 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 2.46. In 2007, the star's

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 ...

was measured at yielding a distance of 15 parsecs or approximately 49 light years from Earth.

Interferometry Interferometry is a technique which uses the ''interference (wave propagation), interference'' of Superposition principle, superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important inves ...

by the

CHARA array The CHARA (Center for High Angular Resolution Astronomy) array is an optical interferometer, located on Mount Wilson, California. The array consists of six telescopes operating as an astronomical interferometer. Construction was completed in ...

show that Alderamin has an oblate shape, its equatorial size measures and the polar radius measures . The star's temperature varies as well, from 8,440 K in the poles to 7,600 K in the equator. A more recent but less detailed measurement by the

Navy Precision Optical Interferometer The Navy Precision Optical Interferometer (NPOI) is an American astronomical interferometer, with the world's largest baselines, operated by the Naval Research Laboratory (NRL). Until the end of 2022, it was operated by a consortium that included ...

gives , which likely corresponds to the equatorial radius. Like other stars in its class, it is slightly variable with a range in brightness of 0.06 magnitude, and is listed as a

Delta Scuti variable A Delta Scuti variable (sometimes termed dwarf cepheid when the V-band amplitude is larger than 0.3 mag.) is a class of pulsating star, comprising several sub-classes of object with A- or F-type spectra. The variables follow a period-luminosity ...

. Alderamin has a very high rotation speed of at least 246 km/s, completing one complete revolution in less than 12 hours, with such a rapid turnover appearing to inhibit the differentiation of chemical elements usually seen in such stars. By comparison, the Sun takes almost a month to turn on its axis. Alpha Cephei is also known to emit an amount of X radiation similar to the Sun, which along with other indicators suggests the existence of considerable magnetic activity—something unexpected (though not at all unusual) for a fast rotator.

Etymology and cultural significance

This star, along with

Beta Cephei Beta Cephei (β Cephei, abbreviated Beta Cep, β Cep) is a triple star system of the third magnitude in the constellation of Cepheus. Based on parallax measurements obtained during the Hipparcos mission, it is approximately 690 light-y ...

(Alfirk) and

Eta Cephei Eta Cephei (η Cep, η Cephei) is a star in the northern circumpolar constellation of Cepheus. With an apparent visual magnitude of 3.4, this is a third magnitude star that, according to the Bortle Dark-Sky Scale, is readily visible to ...

(Alkidr) were ''al-Kawākib al-Firq'' (''الكواكب الفرق''), meaning "the Stars of the Flock" by

Ulug Beg Mīrzā Muhammad Tarāghāy bin Shāhrukh (; ), better known as Ulugh Beg (; 22 March 1394 – 27 October 1449), was a Timurid sultan, as well as an astronomer and mathematician. Ulugh Beg was notable for his work in astronomy-related ma ...

. In

Chinese Chinese may refer to: * Something related to China * Chinese people, people identified with China, through nationality, citizenship, and/or ethnicity **Han Chinese, East Asian ethnic group native to China. **'' Zhonghua minzu'', the supra-ethnic ...

, (), meaning '' Celestial Hook'', refers to an asterism consisting of α Cephei,

4 Cephei 4 (four) is a number, numeral and digit. It is the natural number following 3 and preceding 5. It is a square number, the smallest semiprime and composite number, and is considered unlucky in many East Asian cultures. Evolution of the Hi ...

HD 194298 HD may refer to: Business * H-D or Harley-Davidson, a motorcycle manufacturer * The Home Depot, NYSE stock symbol: HD Chemistry * Hydrogen deuteride, a diatomic compound of hydrogen and deuterium * Mustard gas Codes * Air Do, formerly Ho ...

, Theta Cephei, Xi Cephei,

26 Cephei 6 (six) is the natural number following 5 and preceding 7. It is a composite number and the smallest perfect number. In mathematics A six-sided polygon is a hexagon, one of the three regular polygons capable of tiling the plane. A hexagon a ...

Iota Cephei Iota Cephei (ι Cephei, ι Cep) is a star in the northern constellation Cepheus. Based upon an annual parallax shift of as seen from the Earth, it is located about from the Sun. The star is visible to the naked eye with an apparent visua ...

and

Omicron Cephei Omicron Cephei, Latinized from ο Cephei, is a binary star in the constellation of Cepheus. It consists of a less massive F-type main sequence star in orbit with a more massive G-type giant star. The overall apparent visual ...

. Consequently, the

Chinese name Chinese may refer to: * Something related to China * Chinese people, people identified with China, through nationality, citizenship, and/or ethnicity **Han Chinese, East Asian ethnic group native to China. **'' Zhonghua minzu'', the supra-ethni ...

for Alpha Cephei itself is (, .).

Namesakes

USS Alderamin (AK-116) 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.

References

External links

* *NASA's
History of Precession
*Crystallinks

{{DEFAULTSORT:Alpha Cephei Cephei, Alpha Cepheus (constellation) A-type subgiants Northern pole stars

Alderamin Alpha Cephei (α Cephei, abbreviated Alpha Cep, α Cep), officially named Alderamin , is a second magnitude star in the constellation of Cepheus near the northern pole. The star is relatively close to Earth at 49 light years (''ly'') ...

Castor Moving Group Cephei, 05 203280 8162 BD+61 2111 105199 Suspected variables Delta Scuti variables 0826