Arcturus is the brightest star in the constellation of Boötes, the fourth-brightest in the night sky, and the brightest in the northern celestial hemisphere.
Together with Spica and Denebola (or Regulus, depending on the source), Arcturus is part of the Spring Triangle asterism and, by extension, also of the Great Diamond along with the star Cor Caroli.
Relatively close at 36.7 light-years from the Sun, Arcturus is a red giant of spectral type K0III—an aging star around 7.1 billion years old that has used up its core hydrogen and moved off the main sequence.
One astronomical tradition associates Arcturus with the mythology around Arcas, who was about to shoot and kill his own mother Callisto who had been transformed into a bear.
Zeus averted their imminent tragic fate by transforming the boy into the constellation Boötes, called Arctophylax “bear guardian” by the Greeks, and his mother into Ursa Major (Greek: Arctos “the bear”). The account is given in Hyginus’s Astronomy.
Aratus in his Phaenomena said that the star Arcturus lay below the belt of Arctophylax, although according to Ptolemy in the Almagest it lay between his thighs.
Alternative lore associates the name with the legend around Icarius, who gave the gift of wine to other men, but was murdered by them because they had had no experience with intoxication and mistook the wine for poison.
It is stated that Icarius, became Arcturus, while his dog, Maira, became Canicula (Procyon), although “Arcturus” here may be used in the sense of the constellation rather than the star.
In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars.
The WGSN’s first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN; which included Arcturus for this star. It is now so entered in the IAU Catalog of Star Names.
Astronomers term “metals” those elements with higher atomic numbers than helium. Arcturus has an enrichment of alpha elements relative to iron but only about a third of solar metallicity. It is possibly a Population II star.
Possible planetary system
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 humans’ current ability to make it out. Recent results remain inconclusive but do support the marginal Hipparcos detection of a binary companion.
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 at the same orbital distance from Arcturus as the Earth is from the Sun, 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.
In Arabic, Arcturus is one of two stars called al-simāk “the uplifted ones” (the other is Spica). Arcturus is specified as-simāk ar-rāmiħ “the uplifted one of the lancer“. The term Al Simak Al Ramih has appeared in Al Achsasi Al Mouakket catalog.
This has been variously romanized in the past, leading to obsolete variants such as Aramec and Azimech. For example, the name Alramih is used in Geoffrey Chaucer’s A Treatise on the Astrolabe (1391).
Arcturus was once again called by its classical name from the Renaissance onwards.
In Chinese astronomy, Arcturus is called Da Jiao, because it is the brightest star in the Chinese constellation called Jiao Xiu (Chinese: pinyin: Jiǎo Xiǔ; literally: ‘horn star’). Later it became a part of another constellation Kang Xiu.
In Indian Astrology or Vedic Astrology or Sidereal Astrology, Arcturus is called Swati which is a word meaning “very beneficent” derived from the language Sanskrit. It is the eponymous star of one of the nakshatras (lunar mansions) of Hindu astrology.
The Wotjobaluk Koori people of southeastern Australia knew Arcturus as Marpean-kurrk, mother of Djuit (Antares) and another star in Boötes, Weet-kurrk (Muphrid).
Its appearance in the north signified the arrival of the 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 people of Milingimbi Island in Arnhem Land saw Arcturus and Muphrid as man and woman and took the appearance of Arcturus at sunrise as a sign to go and harvest rakia or spike rush. The Wailwun of northern New South Wales knew Arcturus as Guembila “red”.
In Inuit astronomy, Arcturus is called the Old Man (Uttuqalualuk in Inuit languages) and The First Ones (Sivulliik in Inuit languages).
Arcturus had several names that described its significance to indigenous Polynesians. In the Society Islands, Arcturus, called Ana-tahua-taata-metua-te-tupu-mavae (“a pillar to stand by”), was one of the ten “pillars of the sky”, bright stars that represented the ten heavens of the Tahitian afterlife.
In Hawaii, the pattern of Boötes was called Hoku-iwa, meaning “stars of the frigatebird”. This constellation marked the path for Hawaiiloa on his return to Hawaii from the South Pacific Ocean. The Hawaiians called Arcturus Hoku-leʻa. It was equated to the Tuamotuan constellation Te Kiva, meaning “frigatebird“, which could either represent the figure of Boötes or just Arcturus.
However, Arcturus may instead be the Tuamotuan star called Turu. The Hawaiian name for Arcturus as a single star was likely Hoku-leʻa, which means “star of gladness“, or “clear star“.
In the Marquesas Islands, Arcturus was probably called Tau-tou and was the star that ruled the month of approximating January. The Māori and Moriori called it Tautoru, a variant of the Marquesan name and a name shared with Orion’s Belt.
- 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 Hōkūleʻa has crossed the Pacific Ocean many times under navigators who have incorporated this wayfinding technique in their non-instrument navigation.
- In ancient Mesopotamia, it was linked to the god Enlil, and also known as Shudun, “yoke“, or SHU-PA of unknown derivation in the Three Stars Each Babylonian star catalogues and later MUL.APIN around 1100 BC.
- In Ancient Rome, the star’s celestial activity was supposed to portend tempestuous weather, and a personification of the star acts as narrator of the prologue to Plautus’ comedy Rudens (circa 211 BC).
- In the Hebrew scriptures Arcturus is referred to in Job 38:32.
- In the Middle Ages, Arcturus was considered a Behenian fixed star and attributed to the stone Jasper and the plantain herb. Cornelius Agrippa listed its kabbalistic sign Agrippa1531 Alchameth.png under the alternate name Alchameth.
- The Karandavyuha sutra, compiled at the end of the 4th century or beginning of the 5th century, names one of Avalokiteshvara’s meditative absorptions as “The face of Arcturus“.
- One of the possible etymologies offered for the name “Arthur” assumes that it is derived from “Arcturus” and that the early Medieval character on whom the myth of King Arthur is based was originally named for the star