Groombridge 1830
Encyclopedia
Groombridge 1830 is a star
in the constellation
Ursa Major
.
subdwarf catalogued by Stephen Groombridge
with the Groombridge Transit Circle
between 1806 and the 1830s and published posthumously in his star catalog, Catalogue of Circumpolar Stars (1838). Its high proper motion
was noted by Friedrich Wilhelm Argelander
in 1842.
It is 29.7 light years from Earth
's Solar System
, which means its absolute magnitude
is almost equal to its apparent magnitude
. It is a halo
star; such stars account for only 0.1 to 0.2 percent of the stars near the Sun
. Like most halo stars, it is metal-poor
.
Once suspected of being a binary star
with a period of 175 days, current consensus is that it is single. In fact, previous suspected observations of a stellar companion were probably "superflares"—analogous to the Sun's solar flare
s, but hundreds to millions of times more energetic.
of any star known, replacing 61 Cygni
in that department. Later it dropped to second place after the discovery of Kapteyn's Star
, and still later to third place after the discovery of Barnard's Star
. It is considerably farther away than either of those stars, however, which means its transverse velocity is greater.
Actually, it is the Sun which is following the motion of galaxy rotation by revolving around the center of the Milky Way
; halo stars like Groombridge 1830 do not follow this galaxy rotation and thus are "standing still" and appear to be moving in "retrograde direction" at high speed.
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....
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...
.
Description
It is a yellowish class G8Stellar 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...
subdwarf catalogued by Stephen Groombridge
Stephen Groombridge
Stephen Groombridge FRS was a British astronomer.In 1806, using a then new transit circle built by Edward Troughton, he began compiling a star catalogue of stars down to about eighth or ninth magnitude...
with the Groombridge Transit Circle
Groombridge Transit Circle
Groombridge Transit Circle was a meridian transit circle made by Edward Troughton for Stephen Groombridge in 1806, which Groombridge used to compile data for the star catalogue, Catalogue of Circumpolar Stars. The advantage of a transit circle over a mural circle is that it allows measuring right...
between 1806 and the 1830s and published posthumously in his star catalog, Catalogue of Circumpolar Stars (1838). Its high proper motion
Proper motion
The proper motion of a star is its angular change in position over time as seen from the center of mass of the solar system. It is measured in seconds of arc per year, arcsec/yr, where 3600 arcseconds equal one degree. This contrasts with radial velocity, which is the time rate of change in...
was noted by Friedrich Wilhelm Argelander
Friedrich Wilhelm Argelander
Friedrich Wilhelm August Argelander was a German astronomer. He is known for his determinations of stellar brightnesses, positions, and distances.- Life and work :...
in 1842.
It is 29.7 light years 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...
's 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...
, which means its absolute magnitude
Absolute magnitude
Absolute magnitude is the measure of a celestial object's intrinsic brightness. it is also the apparent magnitude a star would have if it were 32.6 light years away from Earth...
is almost equal to 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...
. It is a halo
Galactic halo
The term galactic halo is used to denote an extended, roughly spherical component of a galaxy, which extends beyond the main, visible component. It can refer to any of several distinct components which share these properties:* the galactic spheroid...
star; such stars account for only 0.1 to 0.2 percent of the stars near the 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...
. Like most halo stars, it is metal-poor
Metallicity
In astronomy and physical cosmology, the metallicity of an object is the proportion of its matter made up of chemical elements other than hydrogen and helium...
.
Once suspected of being 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 period of 175 days, current consensus is that it is single. In fact, previous suspected observations of a stellar companion were probably "superflares"—analogous to the Sun's solar flare
Solar flare
A solar flare is a sudden brightening observed over the Sun surface or the solar limb, which is interpreted as a large energy release of up to 6 × 1025 joules of energy . The flare ejects clouds of electrons, ions, and atoms through the corona into space. These clouds typically reach Earth a day...
s, but hundreds to millions of times more energetic.
Proper motion
When discovered, it had the highest proper motionProper motion
The proper motion of a star is its angular change in position over time as seen from the center of mass of the solar system. It is measured in seconds of arc per year, arcsec/yr, where 3600 arcseconds equal one degree. This contrasts with radial velocity, which is the time rate of change in...
of any star known, replacing 61 Cygni
61 Cygni
61 Cygni,Not to be confused with 16 Cygni, a more distant system containing two G-type stars harboring the gas giant planet 16 Cygni Bb. sometimes called Bessel's Star or Piazzi's Flying Star, is a binary star system in the constellation Cygnus...
in that department. Later it dropped to second place after the discovery of Kapteyn's Star
Kapteyn's Star
Kapteyn's Star is a class M1 red dwarf star about 13 light years from Earth in the southern constellation of Pictor. With a magnitude of nearly 9 it is visible through binoculars or a telescope.-History:...
, and still later to third place after the discovery of Barnard's Star
Barnard's star
Barnard's Star, also known occasionally as Barnard's "Runaway" Star, is a very low-mass red dwarf star approximately six light-years away from Earth in the constellation of Ophiuchus . In 1916, the American astronomer E.E...
. It is considerably farther away than either of those stars, however, which means its transverse velocity is greater.
Actually, it is the Sun which is following the motion of galaxy rotation by revolving around the center of the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
; halo stars like Groombridge 1830 do not follow this galaxy rotation and thus are "standing still" and appear to be moving in "retrograde direction" at high speed.
Discovery of high proper motion
- AN 19 (1842) 393/394 (in German)
- AN 20 (1843) 163/164 (in German)
- AN 20 (1843) 279/280