Arcturus
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 Arcturus in the constellation of Boötes. |
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| Observation data Equinox J2000 |
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|---|---|
| Constellation | Boötes |
| Right ascension | 14h 15m 39.7s |
| Declination | +19° 10' 56" |
| Apparent magnitude (V) | −0.04 |
| Characteristics | |
| Spectral type | K1.5 IIIpe |
| U-B color index | 1.22 |
| B-V color index | 1.24 |
| Variable type | Suspected |
| Astrometry | |
| Radial velocity (Rv) | −5.2 km/s |
| Proper motion (μ) | RA: −1093.45 mas/yr Dec.: −1999.40 mas/yr |
| Parallax (π) | 88.78 ± 0.68 mas |
| Distance | 36.7 ± 0.3 ly (11.26 ± 0.09 pc) |
| Absolute magnitude (MV) | −0.38 |
| Details | |
| Mass | 1–1.5 M☉ |
| Radius | 15.9 R☉ |
| Luminosity | 110 L☉ |
| Temperature | 4,300 K |
| Metallicity | 20–50% Sun |
| Rotation | |
| Age | > 4.6 × 109 years |
| Other designations | |
| Database references | |
| SIMBAD | data |
Arcturus (α Boo / α Boötis / Alpha Boötis) (IPA: [aɹkˈtjuɹəs]) is the brightest star in the constellation Boötes, and the third brightest star in the night sky, with a visual magnitude of −0.05, after Sirius and Canopus. Because Alpha Centauri consists of two bright stars which are closer together than the limit of resolution of the human eye, Alpha Centauri actually appears brighter than Arcturus to the naked eye. It is the second brightest star visible from northern latitudes and the brightest star in the northern celestial hemisphere. The star is in the Local Interstellar Cloud.
An easy way to find Arcturus is to follow the arc of the handle of the Big Dipper. By continuing in this path, one can find Spica (α Virginis) as well — leading to the coinage of the popular maxim, "Arc to Arcturus, then speed on to Spica."
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[edit] Etymology
The name of the star derives from ancient Greek Αρκτούρος (Arktouros) and means "Bear Guard." This is a reference to it being the brightest star in the constellation Boötes the Hunter (of which it forms the left foot), which is next to the Big and Little Bears, Ursa Major and Ursa Minor. There is also a Greek non-governmental environmental organization named Αρκτούρος that protects wild life.
In Arabic, it is called As-Simak ar-Ramih (السماك الرامح) which has been translated as "leg of the lance-bearer" or "the lofty lance-bearer." This name has been variously romanized in the past, leading to obsolete variants such as Aramec and Azimech. Another Arabic name is Al-Harith as-Sama' (الحارث السماء), "the keeper of heaven."[1][2][3]
In Chinese astronomy, Arcturus is called Dah Jyaoo (大角, Great Horn, Pinyin: Dajiao), because it is the brightest star in the Chinese constellation called Jyaoo Shiuh (角宿, Pinyin: Jiaosu). And later, it become a part of Kangh Shiuh (亢宿, Pinyin: Kangsu), which is also a Chinese constellation.
Ancient Japanese astronomy adopt Chinese name "大角", but its western name (アルクトゥルス) is more common now.[citation needed]
It corresponds to the Hindu astronomy Nakshatra of Svātī.
[edit] Stellar system
It is a type K1.5 IIIpe red giant star — the letters "pe" stand for "peculiar emission," which indicates that the spectrum of light given off by the star is unusual and full of emission lines. This is not too uncommon in red giants, but Arcturus has a particularly strong case of the phenomenon. It is at least 110 times more luminous than the Sun, but this underestimates its strength as much of the "light" it gives off is in the infrared; total power output is about 180 times that of the Sun. The lower output in visible light is due to a lower efficacy as the star has a lower surface temperature than the Sun.
Arcturus is notable for its high proper motion, larger than any first magnitude star in the stellar neighbourhood other than α Centauri. It is now almost [4] at its closest point to the Sun, and is moving rapidly (122 km/s) relative to the solar system. Arcturus is thought to be an old disk star, and appears to be moving with a group of 52 other such stars. Its mass is hard to exactly determine, but may be about the same as the Sun, and is no more than 1.5 solar masses. Arcturus is likely to be considerably older than the Sun, and much like what the Sun will be in its red giant phase.
According to the Hipparcos satellite, Arcturus is 36.7 light years (11.3 parsecs) from Earth, relatively close in astronomical terms. Hipparcos also suggested that Arcturus is a binary star, with the companion about twenty times dimmer than the primary and orbiting close enough to be at the very limits of our current ability to make it out. The most recent studies of the issue are generally coming down on the side of it being a single star, however.[1]
[edit] Seismology
As one of the brightest stars in the sky, Arcturus has been the subject of a number of studies in the emerging field of astroseismology.
Belmonte et al. (1990) carried out a radial velocity (Doppler shift of spectral lines) study of the star in April and May 1988, which showed variability with a frequency of the order of a few microhertz, the highest peak corresponding to 4.3 μHz (2.7 days) with an amplitude of 60 ms-1, with a frequency separation of ~5 μHz. They suggested that the most plausible explanation for the variability of Arcuturus is stellar oscillations.
High precision photometry from the Hipparcos satellite's observations showed Arcturus is now known to be slightly variable, by about 0.04 magnitudes over 8.3 days.[citation needed] It is believed that the surface of the star oscillates slightly, a common feature of red giant stars. In the case of Arcturus, this was an interesting discovery as it is known that the redder (more towards or within the M spectral class) a giant gets, the more variable it will be. Extreme cases like Mira undergo large swings over hundreds of days; Arcturus is not very red and is a borderline case between variability and stability with its short period and tiny range.
[edit] Cultural significance
Prehistoric Polynesian navigators knew Arcturus as Hokule'a, the "Star of Joy." Arcturus is the Zenith Star of the Hawaiian Islands. Using Hokule'a and other stars, the Polynesians launched their double-hulled canoes from Tahiti and the Marquesas Islands. Traveling east and north they eventually crossed the equator and reached the latitude where Arcturus would appear directly overhead in the summer night sky. Knowing they had arrived at the exact latitude of the island chain, they sailed due west on the trade winds until making landfall. If Hokule'a could be kept directly overhead, they landed on the southeastern shores of the Big Island of Hawaii. For a return trip to Tahiti the navigators could use Sirius, the zenith star of that island.
The star achieved fame in 1933 when its light was used to open the World's Fair in Chicago, Illinois. The star was chosen as it was thought that light from Arcturus had started its journey at about the time of the previous Chicago fair in 1893. Technically the star is 36.7 light years away so the light would have started its journey in 1896.
[edit] New Age
Some New Agers believe in Arcturians, a highly advanced extraterrestrial race.
[edit] Edgar Cayce
In a reading in which the 'sleeping prophet' describes philosophical concepts as they relate to religious tenets, Cayce mentions Arcturus.
(Q) The sixth problem concerns interplanetary and inter-system dwelling, between earthly lives. It was given through this source that the entity Edgar Cayce, after the experience as Uhjltd, went to the system of Arcturus, and then returned to earth. Does this indicate a usual or an unusual step in soul evolution?
(A) As indicated, or as has been indicated in other sources besides this as respecting this very problem, - Arcturus is that which may be called the center of this universe, through which individuals pass and at which period there comes the choice of the individual as to whether it is to return to complete there - that is, in this planetary system, our sun, the earth sun and its planetary system - or to pass on to others. This was an unusual step, and yet a usual one. (5749-14)
[edit] Biblical
In the King James Version of the Bible, Arcturus is mentioned twice in the Book of Job:
- "Which maketh Arcturus, Orion, and Pleiades, and the chambers of the south."
- "Canst thou bring forth Mazzaroth in his season?
- or canst thou guide Arcturus with his sons?"
The Hebrew word thus translated is עיש Ash or 'Ayish. Due to the obscurity of ancient terminology, some scholars dispute this identification, instead equating it with Aldebaran, Canopus, Ursa Major, or the Pleiades, among other celestial objects.[5]
[edit] Occult traditions
In the astrology of the Middle Ages, Arcturus was one of the 15 Behenian fixed stars, associated with jasper and the plantain herb. Cornelius Agrippa lists its symbol 
under the alternate name Alchameth.
[edit] See also
[edit] References
- ^ List of the 25 brightest stars, website of the Jordanian Astronomical Society, accessed March 28, 2007.
- ^ Richard Hinckley Allen, Star-names and their meanings (1936), p. 100-101.
- ^ Hans Wehr (J.M. Cowan ed.), A dictionary of modern written Arabic (1994).
- ^ "Almost" on an astronomical timescale. Closest approach will happen in about 4000 years, at a distance of 99.9% the current distance.
- ^ Hirsch, Emil G. (1906). Constellations. In The Jewish Encyclopedia. New York: Funk & Wagnall's. Retrieved July 11, 2005.
[edit] External links
- Illustration comparing the size of Arcturus with other stars
- Discussion of Arcturus' role in Marvel comics
- SolStation.com entry
Categories: Articles lacking sources from December 2006 | All articles lacking sources | Articles with unsourced statements since February 2007 | All articles with unsourced statements | Bayer objects | Boötes constellation | Flamsteed objects | HD and HDE objects | HIP objects | Orange giants | Red giants | Suspected variables
