Alpha Herculis
Encyclopedia
Alpha Herculis (α Her, α Herculis) is a multiple star system
in the constellation
Hercules
. It has the traditional name Rasalgethi or Ras Algethi ( Head of the Kneeler), and the Flamsteed designation
64 Herculis. The traditional name "Head" comes from the fact that in antiquity Hercules was depicted upside down on the constellation maps.
The term ra's al-jaθiyy or Ras al Djathi was appeared in the catalogue of stars in the Calendarium of Al Achsasi al Mouakket
, which was translated into Latin
as Caput Ingeniculi.
In Chinese astronomy
, Rasalgethi is called 帝座, Pinyin
: Dìzuò, meaning Emperor's Seat, because this star is marking itself and stand alone in Emperor's Seat asterism, Heavenly Market enclosure
(see : Chinese constellation
). 帝座 (Dìzuò) was westernized into Ti Tso by R.H. Allen, with the same meaning
34 ± 0.8 mas, or 0.034 arcseconds. At an estimated distance of 110 parsec
s, this corresponds to a radius of about 280 million kilometers (or 170 million miles), which is roughly 400R☉ or 1.87 AU
. If Rasalgheti were at the center of our Solar System
its radius would extend past the orbit of Mars
at 1.5 AU
but not quite as far as the asteroid belt
. The red giant is estimated to have started its life with about 7-8 solar mass
es. Like most type M stars near the end of their lives, Rasalgethi is experiencing a high degree of stellar mass loss
creating a sparse, gaseous envelope that extends at least 90 astronomical unit
s.
. α2 is actually a double star
system with a primary yellow giant star and a secondary, yellow-white dwarf star. (These components are sometimes designated α Herculis A, Ba and Bb, respectively.)
Star system
A star system or stellar system is a small number of stars which orbit each other, bound by gravitational attraction. A large number of stars bound by gravitation is generally called a star cluster or galaxy, although, broadly speaking, they are also star systems.-Binary star systems:A stellar...
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...
. It has the traditional name Rasalgethi or Ras Algethi ( Head of the Kneeler), and the Flamsteed designation
Flamsteed designation
Flamsteed designations for stars are similar to Bayer designations, except that they use numbers instead of Greek letters. Each star is assigned a number and the Latin genitive of the constellation it lies in...
64 Herculis. The traditional name "Head" comes from the fact that in antiquity Hercules was depicted upside down on the constellation maps.
The term ra's al-jaθiyy or Ras al Djathi was appeared in the catalogue of stars in the Calendarium of Al Achsasi al Mouakket
Al Achsasi al Mouakket
Mohammad Al Achsasi Al Mouakket was an Egyptian astronomer whose calendarium and catalogue of stars, entitled Durret al Muddiah Fih al Aamal al Shamsiah , was written at Cairo about 1650.Al Achsasi was sheikh of the Grand Mosque of the University of Cairo, where his name al...
, which was translated into Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
as Caput Ingeniculi.
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."...
, Rasalgethi is called 帝座, 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...
: Dìzuò, meaning Emperor's Seat, because this star is marking itself and stand alone in Emperor's Seat asterism, Heavenly Market enclosure
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 :...
(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....
). 帝座 (Dìzuò) was westernized into Ti Tso by R.H. Allen, with the same meaning
Properties
The angular diameter of the red giant, α1 Her, has been measured with an interferometer as34 ± 0.8 mas, or 0.034 arcseconds. At an estimated distance of 110 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, this corresponds to a radius of about 280 million kilometers (or 170 million miles), which is roughly 400R☉ or 1.87 AU
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
. If Rasalgheti were at the center of our Solar System
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
its radius would extend past the orbit of Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
at 1.5 AU
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
but not quite as far as the asteroid belt
Asteroid belt
The asteroid belt is the region of the Solar System located roughly between the orbits of the planets Mars and Jupiter. It is occupied by numerous irregularly shaped bodies called asteroids or minor planets...
. The red giant is estimated to have started its life with about 7-8 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...
es. Like most type M stars near the end of their lives, Rasalgethi is experiencing a high degree of stellar mass loss
Stellar mass loss
Stellar mass loss is a phenomenon observed in some massive stars. It occurs when a triggering event causes the ejection of a large portion of the star's mass. Stellar mass loss can also occur when a star gradually loses material to a binary companion or into interstellar space.-Causes:A number of...
creating a sparse, gaseous envelope that extends at least 90 astronomical unit
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
s.
Star system
When viewed through a telescope, this system is resolved into two components designated α1 and α2. These two components are more than 500 astronomical units apart, with an estimated orbital period of approximately 3600 years. α1 is a relatively massive red bright giantBright giant
The luminosity class II in the Yerkes spectral classification is given to bright giants. These are stars which straddle the boundary between giants and supergiants, and the classification is in general given to giant stars with exceptionally high luminosity, but which are not sufficiently bright...
. α2 is actually a double star
Double star
In observational astronomy, a double star is a pair of stars that appear close to each other in the sky as seen from Earth when viewed through an optical telescope. This can happen either because the pair forms a binary star, i.e...
system with a primary yellow giant star and a secondary, yellow-white dwarf star. (These components are sometimes designated α Herculis A, Ba and Bb, respectively.)
See also
- List of largest known stars
- Lists of stars in the constellation Hercules
- Betelgeuse mass loss
- Spectral types F, G & M
External links
- Jim Kaler's Stars, University of Illinois: RASALGETHI (Alpha Herculis)
- An Atlas of the Universe: Multiple Star Orbits
- Upside down Hercules showing Rasalgethi as the head: Hercules