Th'uban is also an enemy in the video game Final Fantasy X

Final Fantasy X

is a role-playing video game developed and published by Square as the tenth title in the Final Fantasy series. It was released in 2001 for Sony's PlayStation 2, and will be re-released for PlayStation 3 and PlayStation Vita in 2012...

.

Thuban also known by its Bayer designation

Bayer designation

A Bayer designation is a stellar designation in which a specific star is identified by a Greek letter, followed by the genitive form of its parent constellation's Latin name...

 Alpha Draconis (α Draconis, α Dra) is a star

Star

A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...

 (or star system) in the constellation

Constellation

In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....

 of Draco

Draco (constellation)

Draco is a constellation in the far northern sky. Its name is Latin for dragon. Draco is circumpolar for many observers in the northern hemisphere...

. A relatively inconspicuous star in the night sky of the Northern Hemisphere

Northern Hemisphere

The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...

, it is historically significant as having been the north pole star

Pole star

The term "Pole Star" usually refers to Polaris, which is the current northern pole star, also known as the North Star.In general, however, a pole star is a visible star, especially a prominent one, that is approximately aligned with the Earth's axis of rotation; that is, a star whose apparent...

 in ancient times. Thuban is an Arabic word for snake

Snake

Snakes are elongate, legless, carnivorous reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears. Like all squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales...

  .

Even though Johann Bayer

Johann Bayer

Johann Bayer was a German lawyer and uranographer . He was born in Rain, Bavaria, in 1572. He began his study of philosophy in Ingolstadt in 1592, and moved later to Augsburg to begin work as a lawyer. He grew interested in astronomy during his time in Augsburg...

 gave Thuban the designation Alpha

Alpha

Alpha is the first letter of the Greek alphabet. Alpha or ALPHA may also refer to:-Science:*Alpha , the highest ranking individuals in a community of social animals...

, its apparent magnitude

Apparent magnitude

The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...

 of 3.65 is 3.7 times fainter than the brightest star in the constellation, Gamma Draconis (Eltanin), whose apparent magnitude is 2.24.

Visibility

Given good viewing conditions, Thuban is relatively easy to spot in the night sky, due to its location in relation to the Big Dipper

Big Dipper

The Plough, also known as the Big Dipper or the Saptarishi , is an asterism of seven stars that has been recognized as a distinct grouping in many cultures from time immemorial...

 asterism

Asterism (astronomy)

In astronomy, an asterism is a pattern of stars recognized on Earth's night sky. It may form part of an official constellation, or be composed of stars from more than one. Like constellations, asterisms are in most cases composed of stars which, while they are visible in the same general direction,...

 of Ursa Major

Ursa Major

Ursa Major , also known as the Great Bear, is a constellation visible throughout the year in most of the northern hemisphere. It can best be seen in April...

. While it is well known that the two outer stars of the 'dipper' point to the modern-day pole star

Pole star

The term "Pole Star" usually refers to Polaris, which is the current northern pole star, also known as the North Star.In general, however, a pole star is a visible star, especially a prominent one, that is approximately aligned with the Earth's axis of rotation; that is, a star whose apparent...

 Polaris

Polaris

Polaris |Alpha]] Ursae Minoris, commonly North Star or Pole Star, also Lodestar) is the brightest star in the constellation Ursa Minor. It is very close to the north celestial pole, making it the current northern pole star....

, it is less well known that the two inner stars, Phecda

Gamma Ursae Majoris

Gamma Ursae Majoris is a star in the constellation Ursa Major. It has the traditional name Phad, or Phecda, from the Arabic phrase فخذ الدب "fakhð ad-dubb" ....

 and Megrez

Delta Ursae Majoris

Delta Ursae Majoris is a star in the constellation Ursa Major. It has the traditional names Megrez , from the al-maghriz "the base [of the bear's tail]", and Kaffa....

, point to Thuban, just 15 degrees of arc from Megrez. Thuban is not bright enough to be viewed from light-polluted

Light pollution

Light pollution, also known as photopollution or luminous pollution, is excessive or obtrusive artificial light.The International Dark-Sky Association defines light pollution as:...

 areas.

Pole star

Due to the precession of Earth

Earth

Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

's rotational axis, Thuban was the naked-eye star closest to the north pole

North Pole

The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is, subject to the caveats explained below, defined as the point in the northern hemisphere where the Earth's axis of rotation meets its surface...

 from 3942 BC, when it moved farther north than Theta Boötis

Theta Boötis

Theta Boötis is a star in the constellation Boötes. It has the traditional name Asellus Primus and the Flamsteed designation 23 Boötis....

, until 1793 BC, when it was superseded by Kappa Draconis

Kappa Draconis

Kappa Draconis is a blue giant star located in the constellation Draco. At an apparent magnitude of 3.88, it is barely visible to the naked eye when artificial lighting from cities is present. Nevertheless, it is a powerful star, approximately five time as massive as the Sun...

. It was closest to the pole in 2787 BC, when it was less than two and a half arc-minutes away from the pole. It remained within one degree of true north for nearly 200 years afterwards, and even 900 years after its closest approach, was just five degrees off the pole. Thuban was considered the pole star until about 1900 BC, when the much brighter Kochab

Beta Ursae Minoris

Beta Ursae Minoris is the second brightest star in the bowl of the "Little Dipper,"the constellation Ursa Minor. It has the traditional name Kochab. Kochab's magnitude is 2.07. It is 16 degrees from Polaris. The star is an orange giant and is 126.4 ± 2.5 light years from Earth. It is 130 times...

 began to approach the pole as well.

Having gradually drifted away from the pole over the last 4,800 years, Thuban is now seen in the night sky at a declination

Declination

In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...

 of 64° 20' 45.6", RA

Right ascension

Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...

 14h 04m 33.58s. After moving nearly 47 degrees off the pole by 10000 AD, Thuban will gradually move back toward the north celestial pole. In 20346 AD, it will again be the pole star, that year reaching a maximum declination of 88° 43' 17.3", RA 19h 08m 54.17s.

Preceded by	Pole Star Pole star The term "Pole Star" usually refers to Polaris, which is the current northern pole star, also known as the North Star.In general, however, a pole star is a visible star, especially a prominent one, that is approximately aligned with the Earth's axis of rotation; that is, a star whose apparent...	Succeeded by
(unknown)	c. 4000 BC–1900 BC	Kochab & Pherkad

Properties

Thuban has a spectral class

Stellar classification

In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...

 of A0III, indicating its similarity to Vega

Vega

Vega is the brightest star in the constellation Lyra, the fifth brightest star in the night sky and the second brightest star in the northern celestial hemisphere, after Arcturus...

 in temperature and spectrum

Electromagnetic spectrum

The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object....

, but more powerful and more massive. Thuban is not a main sequence

Main sequence

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 Hertzsprung and Henry Norris Russell...

 star; it has now ceased hydrogen

Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 fusion

Nuclear fusion

Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...

 in its core and is fusing helium

Helium

Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...

. That makes it a white giant star, being 250 times more powerful than our Sun

Sun

The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

 but over 300 light-year

Light-year

A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...

s distant.

Thuban has no real anomalies other than the relative rarity of being a giant star in the A class, which is usually reserved for main sequence stars and the occasional supergiant. This indicates that Thuban has not been a giant star for very long and may well still be in the process of expanding, probably to eventually become a K class red-orange giant of the Aldebaran

Aldebaran

Aldebaran is a red giant star located about 65 light years away in the zodiac constellation of Taurus. With an average apparent magnitude of 0.87 it is the brightest star in the constellation and is one of the brightest stars in the nighttime sky...

 sort. It may also mean that it has recently run out of helium to fuse and is contracting before starting to burn carbon

Carbon

Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

, in which case it may end up a blue giant

Blue giant

In astronomy, a blue giant is a star with a spectral type of O or B and a luminosity class of III...

 such as Beta Centauri

Beta Centauri

Beta Centauri , also known as Hadar or Agena, is the second brightest star in the constellation Centaurus and the tenth brightest star in the night sky. Beta Centauri is a B1 III blue-white giant star that the astrometric Hipparcos satellite calculates as about 161 parsecs or 525 light-years from...

.

Thuban is a binary star

Binary star

A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...

, with a companion star in a 51-day orbit. The companion has not been directly imaged, and from its mass is probably a red dwarf

Red dwarf

According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool star, of the main sequence, either late K or M spectral type....

 or a low mass white dwarf

White dwarf

A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...

.

Etymology

In Chinese

Chinese language

The Chinese language is a language or language family consisting of varieties which are mutually intelligible to varying degrees. Originally the indigenous languages spoken by the Han Chinese in China, it forms one of the branches of Sino-Tibetan family of languages...

, , meaning Right Wall of Purple Forbidden Enclosure

Purple Forbidden enclosure

The Purple Forbidden enclosure is one of the San Yuan or Three enclosures. Stars and constellations of this group lie near the north celestial pole and visible all year from temperate latitudes in the Northern Hemisphere.-Asterisms:The asterisms are :...

, refers to an asterism consisting of α Draconis, κ Draconis

Kappa Draconis

Kappa Draconis is a blue giant star located in the constellation Draco. At an apparent magnitude of 3.88, it is barely visible to the naked eye when artificial lighting from cities is present. Nevertheless, it is a powerful star, approximately five time as massive as the Sun...

, λ Draconis

Lambda Draconis

Lambda Draconis is a star in the constellation Draco. It has the traditional names Gianfar, Giansar, Juza, Giausar or Giauzar....

, 24 Ursae Majoris, 43 Camelopardalis

43 Camelopardalis

43 Camelopardalis is a star in the constellation Camelopardalis.43 Camelopardalis is a blue-white B-type giant with an apparent magnitude of +5.11...

, α Camelopardalis

Alpha Camelopardalis

Alpha Camelopardalis is an O-type supergiant star, with an apparent visual magnitude of approximately 4.301. It is the third brightest star in the constellation of Camelopardalis, the first and second brightest being β Camelopardalis and CS Camelopardalis, respectively...

 and BK Camelopardalis

BK Camelopardalis

BK Camelopardalis is a variable star in the Camelopardalis.-Chinese name:In Chinese, , meaning Right Wall of Purple Forbidden Enclosure, refers to an asterism consisting of BK Camelopardalis, α Draconis, κ Draconis, λ Draconis, 24 Ursae Majoris, 43 Camelopardalis and α Camelopardalis...

. Consequently, α Draconis itself is known as , representing , meaning Right Pivot. 右樞 (Yòushū) is westernized into Yu Choo by R.H. Allen with the same meaning.

See also

• Lists of stars in the constellation Draco
• Class A Stars
• Giant star
  Giant star
  A giant star is a star with substantially larger radius and luminosity than a main sequence star of the same surface temperature. Typically, giant stars have radii between 10 and 100 solar radii and luminosities between 10 and 1,000 times that of the Sun. Stars still more luminous than giants are...
  
  
• Thuban in fiction

External links

• Jim Kaler's Stars, University of Illinois:THUBAN (Alpha Draconis)
• NASA's: History of Precession
• Crystalinks:Precession of the Equinoxes