 Arcturus in the constellation of Boötes. |
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| Observation
data Epoch J2000 Equinox J2000 |
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|---|---|
| Constellation | Boötes |
| Pronunciation | /ɑrkˈtjʊərəs/ |
| Right ascension | 14h 15 m 39.7s |
| Declination | +19° 10' 56" |
| Apparent magnitude (V) | −0.04 |
| Characteristics | |
| Spectral type | K1.5IIIFe-0.5 |
| U-B color index | 1.27 |
| B-V color index | 1.23 |
| R-I color index | 0.65 |
| Variable type | Variable star |
| note (category: variability): | H and K emission vary. |
| Astrometry | |
| Radial velocity (Rv) | +5 km/s |
| Proper motion (μ) | RA: −1093.45 mas/yr Dec.: −1999.40 mas/yr |
| Parallax (π) | 88.98 ± 0.68 mas |
| Distance | 36.7 ± 0.3 ly (11.24 ± 0.09 pc) |
| Absolute magnitude (MV) | −0.29 |
| Details | |
| Mass | 3.5[1] M☉ |
| Radius | 25.7 ± 0.3[2] R☉ |
| Luminosity | 210 ± 10[3] L☉ |
| Temperature | 4,300[4] K |
| Metallicity | 20–50% Sun |
| Rotational velocity (v sin i) | <17 km/s |
| Age | > 4.6 × 109 years |
| Other designations | |
| Database references | |
| SIMBAD | data |
| Data sources: | |
| Hipparcos Catalogue, CCDM (2002), Bright Star Catalogue (5th rev. ed.), VizieR catalog entry |
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Arcturus (α Boo / α Boötis / Alpha Boötis) is the brightest star in the constellation Boötes. With a visual magnitude of −0.05, it is also the third brightest star in the night sky, after Sirius and Canopus. It is, however, fainter than the combined light of the two main components of Alpha Centauri, which are too close together for the eye to resolve as separate sources of light, making Arcturus appear to be the fourth brightest. 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 Plough. By continuing in this path, one can find Spica (α Virginis) as well—hence the maxim, "Arc to Arcturus, then speed on to Spica."
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As one of the brightest stars in the sky, Arcturus has been significant to observers since antiquity. In Ancient Greece, the star's celestial activity was supposed to portend tempestuous weather. For citations see Plautus Rudens prol. 71 and Lewis and Short's Latin Dictionary and its entry for Arcturus.
Prehistoric Polynesian navigators knew Arcturus as Hōkūleʻa, the "Star of Joy". Arcturus is the zenith star of the Hawaiian Islands. Using Hōkūleʻa 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 at which 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 to landfall. If Hōkūleʻa could be kept directly overhead, they landed on the southeastern shores of the Big Island of Hawaiʻi. For a return trip to Tahiti the navigators could use Sirius, the zenith star of that island. Since 1976, the Polynesian Voyaging Society's Hōkūle‘a has crossed the Pacific Ocean many times under navigators who have incorporated this wayfinding technique in their non-instrument navigation.
The Koori people of southeastern Australia knew Arcturus as Marpean-kurrk, and its appearance in the north signified the arrival of larvae of the wood-ant (a food item) in spring. The beginning of summer was marked by the star's setting with the sun in the west and the disappearance of the larvae. The star was also known as the mother of Djuit (Antares), and another star in Bootes, Weet-kurrk.[5]
As one of the brightest stars in the sky, Arcturus has been the subject of a number of studies in the emerging field of asteroseismology.
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. 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.
Arcturus is a type K1.5 IIIpe orange 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 visually 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 neighborhood other than α Centauri. It is moving rapidly (122 km/s) relative to the solar system, and is now almost at its closest point to the Sun. Closest approach will happen in about 4000 years, when the star will be a few hundredths of a light year closer to Earth than it is today. 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 slightly larger than that of the Sun[6] (1.1-0.4+0.6 solar mass). 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. Recent results remain inconclusive, but do support the marginal Hipparcos detection of a binary companion.[7]
In 1993, radial velocity measurements of Aldebaran, Arcturus and Pollux showed that Arcturus exhibited a long-period radial velocity oscillation, which could be interpreted as a substellar companion. This substellar object would be nearly 12 times the mass of Jupiter and be located roughly within Earth's orbital zone, at 1.1 Astronomical Units. However, all three stars surveyed showed similar oscillations yielding similar companion masses, and the authors concluded that the variation was likely to be intrinsic to the star rather than due to the gravitational effect of a companion. So far no substellar companion has been confirmed.[8]
The name of the star derives from Ancient Greek Arktouros/Αρκτοῦρος, and means "Guardian of the Bear". This is a reference to it being the brightest star in the constellation Boötes (of which it forms the left foot), which is next to the Greater and Lesser 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 one of two stars called al-simāk "the uplifted one", the other being Spica. Arcturus, then, is السماك الرامح as-simāk ar-rāmiħ "the uplifted one of the lancer". This has been variously romanized in the past, leading to obsolete variants such as Aramec and Azimech. The name Alramih is used in Geoffrey Chaucer's Treatise on the Astrolabe of 1391. Another Arabic name is Haris-el-sema, from حارس السماء ħāris al-samā’ "the keeper of heaven."[9][10][11]
In Chinese astronomy, Arcturus is called Da Jiao (大角, Great Horn, Pinyin: Dàjiǎo), because it is the brightest star in the Chinese constellation called Jiao Xiu (角宿, Pinyin: Jiǎo Xiǔ). And later, it become a part of Kang Xiu (亢宿, Pinyin: Kàng Xiǔ), which is also a Chinese constellation.
Ancient Japanese astronomy adopted the Chinese name Da Jiao (大角, Ro'ku too), but its western name, Arcturus (アルクトゥルス), is more common now.
In Inuit astronomy, Arcturus is called the Old Man.
It corresponds to the Hindu astronomy Nakshatra of Svātī.
This bright star is the subject of numerous ancient and modern myths.
under the alternate name
Alchameth.Coordinates: 
14h 15m
39.7s, +19° 10′ 56″
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| ←Flame and Shadow | Arcturus by |
Arcturus brings the spring back
As surely now as when
He rose on eastern islands
For Grecian girls and men;
The twilight is as clear a blue,
The star as shaken and as
bright,
And the same thought he gave to them
He gives to me to-night.
 |
This work is in the public domain in
the United States because it was published before
January 1, 1923.
The author died in 1933, so this work is also in the public domain in countries and areas where the copyright term is the author's life plus 75 years or less. This work may also be in the public domain in countries and areas with longer native copyright terms that apply the rule of the shorter term to foreign works. |
ARCTURUS, the brightest star in the northern hemisphere, situated in the constellation Bootes in an almost direct line with the tail Q' and rt) of the constellation Ursa Major (Great Bear); hence its derivation from the Gr. tiprcros, bear, and oupos, guard. Arcturus has been supposed to be referred to in various passages of the Hebrew Bible; the Vulgate reads Arcturus for stars mentioned in Job ix. 9, xxxvii. 9, xxxviii. 31, as well as Amos v. 8. Other versions, as also modern authorities, have preferred, e.g., Orion, the Pleiades, the Scorpion, the Great Bear(cf. Amos in the "International Critical Comment." series,and G. Schiaparelli, Astronomy in the O.T., Eng. trans., Oxford, 1905, ch. iv.). According to one of the Greek legends about Arcas, son of Lycaon, king of Arcadia, he was killed by his father and his flesh was served up in a banquet to Zeus, who was indignant at the crime and restored him to life. Subsequently Areas, when hunting, chanced to pursue his mother Callisto, who had been transformed into a bear, as far as the temple of Lycaean Zeus; to prevent the crime of matricide Zeus transported them both to the heavens (Ovid, Metam. ii. 410), where Callisto became the constellation Ursa Major, and Arcas the star Arcturus (see Lycaon and Callisto).
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From Latin Arctūrus < Ancient Greek Ἀρκτοῦρος (Arktouros) < ἄρκτος (arktos) "bear" + οὖρος (ouros) "guard"
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Singular |
Plural |
Arcturus
From Ancient Greek Ἀρκτοῦρος (Arktouros) < ἄρκτος (arktos) "bear" + οὖρος (ouros) "guard"
Arctūrus
Meaning: bear-keeper
The name given by the ancients to the brightest star in the constellation Bootes. In the Authorized Version (Job 9:9; Job 38:32) it is the rendering of the Hebrew word 'ash, which probably designates the constellation the Great Bear. This word ('ash) is supposed to be derived from an Arabic word meaning night-watcher, because the Great Bear always revolves about the pole, and to our nothern hemisphere never sets.
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| | Illustration comparing the size of Arcturus with other stars - Comparative planetary and stellar sizes |
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