Tau Herculis
Encyclopedia
Tau Herculis (τ Her, τ Herculis) is a fourth-magnitude star
in the constellation
Hercules
. Its traditional name Rukbalgethi Shemali, though seldom used today in scientific journals, shares certain etymological similarities with the stars Ruchbah
and Zubeneschamali
and means the "northern knee". The star was the north pole star
around the year 7400 BC, a phenomenon which is expected to reoccur in the year 18,400 due to precession
.
In Chinese
, , meaning Seven Excellencies
, refers to an asterism consisting of τ Herculis, 42 Herculis, φ Herculis, χ Herculis, ν1 Boötis
, μ1 Boötis
and δ Boötis. Consequently, τ Herculis itself is known as
B5IV. Its mass is 4.9 times solar. Though its apparent magnitude
is only 3.89, like all B-class stars, it is very luminous boasting a total bolometric
luminosity that is 700 times solar. Hipparcos
estimated its distance at roughly 96 parsec
s from Earth
, or 310 ± 20 light years away.
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 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....
Hercules
Hercules (constellation)
Hercules is a constellation named after Hercules, the Roman mythological hero adapted from the Greek hero Heracles. Hercules was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains one of the 88 modern constellations today...
. Its traditional name Rukbalgethi Shemali, though seldom used today in scientific journals, shares certain etymological similarities with the stars Ruchbah
Delta Cassiopeiae
Delta Cassiopeiae is a star in the constellation Cassiopeia. It has the traditional names Ksora and Ruchbah, derived from the Arabic word ركبة rukbah meaning "knee"...
and Zubeneschamali
Beta Librae
Beta Librae is the brightest star in the constellation Libra. It has the traditional name Zubeneschamali and the Latin name Lanx Borealis...
and means the "northern knee". The star was 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...
around the year 7400 BC, a phenomenon which is expected to reoccur in the year 18,400 due to precession
Precession
Precession is a change in the orientation of the rotation axis of a rotating body. It can be defined as a change in direction of the rotation axis in which the second Euler angle is constant...
.
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 Seven Excellencies
Heavenly Market enclosure
Tian Shi Yuan, the Heavenly Market Enclosure , is one of the San Yuan or Three enclosures. Stars and constellations of this group are visible during late summer and early autumn in the Northern Hemisphere . The summer triangle lies directly to the northwest.-Asterisms:The asterisms are :...
, refers to an asterism consisting of τ Herculis, 42 Herculis, φ Herculis, χ Herculis, ν1 Boötis
Nu1 Boötis
Nu1 Boötis is an orange K-type giant with an apparent magnitude of +5.04. It is approximately 872 light years from Earth.-References:* * *...
, μ1 Boötis
Mu Boötis
Mu Boötis is a triple star system in the constellation Boötes. It has the traditional name Alkalurops , and the Flamsteed designation 51 Boötis...
and δ Boötis. Consequently, τ Herculis itself is known as
Properties
Tau Herculis is a B5 subgiant star with stellar classificationStellar 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...
B5IV. Its mass is 4.9 times solar. Though 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...
is only 3.89, like all B-class stars, it is very luminous boasting a total bolometric
Bolometer
A bolometer is a device for measuring the power of incident electromagnetic radiation via the heating of a material with a temperature-dependent electrical resistance. It was invented in 1878 by the American astronomer Samuel Pierpont Langley...
luminosity that is 700 times solar. Hipparcos
Hipparcos
Hipparcos was a scientific mission of the European Space Agency , launched in 1989 and operated between 1989 and 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial objects on the sky...
estimated its distance at roughly 96 parsec
Parsec
The parsec is a unit of length used in astronomy. It is about 3.26 light-years, or just under 31 trillion kilometres ....
s 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...
, or 310 ± 20 light years away.
See also
- Lists of stars in the constellation Hercules
- Class B Stars
- Subgiant starSubgiant starA subgiant star is a star that is slightly brighter than a normal main-sequence star of the same spectral class, but not as bright as true giant stars...
External links
- Jim Kaler's Stars:Tau Herculis