Zeta Tauri
Encyclopedia
Zeta Tauri is a binary star
in the constellation
Taurus
, the Bull. Known to the ancient Babylon
ians as Shurnarkabti-sha-shutu, meaning "the star
in the bull towards the south," Zeta Tauri is among the most prominent of the stars in well-known constellation figures, representing one of the celestial bull's protruding horns.
In Chinese astronomy
, Zeta Tauri is called 天關, Pinyin
: Tiānguān, meaning Celestial Gate, because this star is marking itself and stand alone in Celestial Gate asterism, Net
(mansion) (see : Chinese constellation
). 天關 (Tiānguān) is westernized into Tien Kwan, but the name Tien Kwan was designated not only for Zeta Tauri, but also for the stars near by, with the meaning is "the Heavenly Gate"
giant star
approximately 417 light years
from Earth
. It is classified as a Gamma Cassiopeiae type variable star
. Its brightness varies from magnitude +2.88 to +3.17 due to both its intrinsic variability, and also because it is an eclipsing binary. The two components of the binary system are separated by approximately one astronomical unit
and complete an orbit once every 133 days. Its much lower mass
companion star is a yellow G-type star, which has a magnitude of +5.2. A 9 solar mass
star around 25 million years old, Zeta Tauri is now evolving
, and is close to giving up core hydrogen
fusion
, if it has not done so already.
It radiates the light of approximately 5,700 of our own sun
from a surface heated to 22,000 kelvin
s. Together, temperature
and luminosity
yield a radius
5.2 times that of the Sun. What makes the star really special, however, is not its high temperature and luminosity, but its rotation
and mass loss. The equatorial rotation speed has been measured as high as 330 kilometers per second, which is 115 times that of the Sun, the star spinning around with a period of only one day (as opposed to the 25-day solar rotation period). The rotation, which is still well short of that needed to break up the star, is somehow related to a thick disk of matter that surrounds it. The disk radiates bright emissions from hydrogen
in the red and blue parts of the spectrum
, making Zeta Tauri one the sky's best-known "B-emission" stars. The star and disk are both large enough to have had their angular diameter
s actually measured. The disk is some 64 solar diameters across.
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...
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....
Taurus
Taurus (constellation)
Taurus is one of the constellations of the zodiac. Its name is a Latin word meaning 'bull', and its astrological symbol is a stylized bull's head:...
, the Bull. Known to the ancient Babylon
Babylon
Babylon was an Akkadian city-state of ancient Mesopotamia, the remains of which are found in present-day Al Hillah, Babil Province, Iraq, about 85 kilometers south of Baghdad...
ians as Shurnarkabti-sha-shutu, meaning "the 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...
in the bull towards the south," Zeta Tauri is among the most prominent of the stars in well-known constellation figures, representing one of the celestial bull's protruding horns.
In Chinese astronomy
Chinese astronomy
Astronomy in China has a very long history, with historians considering that "they [the Chinese] were the most persistent and accurate observers of celestial phenomena anywhere in the world before the Arabs."...
, Zeta Tauri is called 天關, Pinyin
Pinyin
Pinyin is the official system to transcribe Chinese characters into the Roman alphabet in China, Malaysia, Singapore and Taiwan. It is also often used to teach Mandarin Chinese and spell Chinese names in foreign publications and used as an input method to enter Chinese characters into...
: Tiānguān, meaning Celestial Gate, because this star is marking itself and stand alone in Celestial Gate asterism, Net
Net (Chinese constellation)
The Net mansion is one of the Twenty-eight mansions of the Chinese constellations. It is one of the western mansions of the White Tiger.-Asterisms:...
(mansion) (see : Chinese constellation
Chinese constellation
Chinese constellations are the way the ancient Chinese grouped the stars. They are very different from the modern IAU recognized constellations. This is because the IAU was based on Greco-Roman astronomy instead of Chinese astronomy....
). 天關 (Tiānguān) is westernized into Tien Kwan, but the name Tien Kwan was designated not only for Zeta Tauri, but also for the stars near by, with the meaning is "the Heavenly Gate"
Properties
Defining mid-third magnitude (3.00), Zeta Tauri is a brilliant hot blue-white B-typeStellar 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...
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...
approximately 417 light years
Light Years
Light Years is the seventh studio album by Australian recording artist Kylie Minogue. It was released on 25 September 2000 by Parlophone and Mushroom Records. The album's style was indicative of her return to "mainstream pop dance tunes"....
from 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...
. It is classified as a Gamma Cassiopeiae type variable star
Variable star
A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
. Its brightness varies from magnitude +2.88 to +3.17 due to both its intrinsic variability, and also because it is an eclipsing binary. The two components of the binary system are separated by approximately one astronomical unit
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
and complete an orbit once every 133 days. Its much lower mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
companion star is a yellow G-type star, which has a magnitude of +5.2. A 9 solar mass
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
star around 25 million years old, Zeta Tauri is now evolving
Stellar evolution
Stellar evolution is the process by which a star undergoes a sequence of radical changes during its lifetime. Depending on the mass of the star, this lifetime ranges from only a few million years to trillions of years .Stellar evolution is not studied by observing the life of a single...
, and is close to giving up core 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...
, if it has not done so already.
It radiates the light of approximately 5,700 of our own 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...
from a surface heated to 22,000 kelvin
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...
s. Together, temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
and luminosity
Luminosity
Luminosity is a measurement of brightness.-In photometry and color imaging:In photometry, luminosity is sometimes incorrectly used to refer to luminance, which is the density of luminous intensity in a given direction. The SI unit for luminance is candela per square metre.The luminosity function...
yield a radius
Radius
In classical geometry, a radius of a circle or sphere is any line segment from its center to its perimeter. By extension, the radius of a circle or sphere is the length of any such segment, which is half the diameter. If the object does not have an obvious center, the term may refer to its...
5.2 times that of the Sun. What makes the star really special, however, is not its high temperature and luminosity, but its rotation
Rotation
A rotation is a circular movement of an object around a center of rotation. A three-dimensional object rotates always around an imaginary line called a rotation axis. If the axis is within the body, and passes through its center of mass the body is said to rotate upon itself, or spin. A rotation...
and mass loss. The equatorial rotation speed has been measured as high as 330 kilometers per second, which is 115 times that of the Sun, the star spinning around with a period of only one day (as opposed to the 25-day solar rotation period). The rotation, which is still well short of that needed to break up the star, is somehow related to a thick disk of matter that surrounds it. The disk radiates bright emissions from 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...
in the red and blue parts of the spectrum
Spectrum
A spectrum is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by...
, making Zeta Tauri one the sky's best-known "B-emission" stars. The star and disk are both large enough to have had their angular diameter
Diameter
In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints are on the circle. The diameters are the longest chords of the circle...
s actually measured. The disk is some 64 solar diameters across.