Η Boötis, or Muphrid, is only 3.3 light-years distant from Arcturus, and would have a visual magnitude −2.5, about as bright as Mercury from Earth, whereas an observer on the former system would find Arcturus as bright as Venus as seen from Earth. Ptolemy described Arcturus as subrufa ("slightly red"): it has a B-V color index of +1.23, roughly midway between Pollux (B-V +1.00) and Aldebaran (B-V +1.54). By continuing in this path, one can find Spica, "Arc to Arcturus, then spike (or speed on) to Spica".
From the northern hemisphere, an easy way to find Arcturus is to follow the arc of the handle of the Big Dipper (or Plough). on June 10 being visible during the late northern spring or the southern autumn. The star culminates at midnight on 27 April, and at 9 p.m. Īrcturus is visible from both of Earth's hemispheres as it is located 19° north of the celestial equator. Arcturus has been seen at or just before sunset with the naked eye. The French mathematician and astronomer Jean-Baptiste Morin observed Arcturus in the daytime with a telescope in 1635, a first for any star other than the Sun and supernovae. This makes Arcturus the third-brightest individual star, just ahead of α Centauri A (officially named Rigil Kentaurus), whose apparent magnitude is −0.01.
However, α Centauri AB is a binary star, whose components are both fainter than Arcturus. With an apparent visual magnitude of −0.05, Arcturus is the brightest star in the northern celestial hemisphere and the fourth-brightest star in the night sky, after Sirius (−1.46 apparent magnitude), Canopus (−0.72) and α Centauri (combined magnitude of −0.27). Observation Īrcturus is the brightest star in the constellation of Boötes. 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 α Boötis. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The designation of Arcturus as α Boötis ( Latinised to Alpha Boötis) was made by Johann Bayer in 1603. The folk-etymology connecting the star name with the bears (Greek: ἄρκτος, arktos) was probably invented much later. Hesiod's Work and Days, Hipparchus's and Ptolemy's star catalogs. The Greek name is found in ancient astronomical literature, e.g. The name Arcturus is Latinised from the Greek star name Ἀρκτοῦρος (arktoyros) meaning "the Guard". It is about the same mass as the Sun, but has expanded to 25 times its size and is around 170 times as luminous. Located relatively close at 36.7 light-years from the Sun, Arcturus is a single red giant of spectral type K1.5III-an aging star around 7.1 billion years old that has used up its core hydrogen and evolved off the main sequence. When viewed from Earth, it appears to be positioned almost at the north galactic pole of the Milky Way. 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. It is designated α Boötis, which is Latinized to Alpha Boötis. Alramech, Alramech, Abramech, α Boötis, Alpha Boo, α Boo, 16 Boötis, BD+19☂777, GJ 541, HD 124897, HIP 69673, HR 5340, SAO 100944, LHS 48, GCTP 3242.00Īrcturus is the brightest star in the northern constellation of Boötes, the fourth-brightest in the night sky, and the brightest in the northern celestial hemisphere.
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