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Arcturus, α Boötis, is the fourth brightest star in the sky at magnitude -0.05.

Declination: 19°10'57" Right Ascension: 14h15m39.7s

It is a K1.5 IIIpe red giant star -- the letters "p" and "e" stand for "peculiar" and "emission", which indicates that the spectrum of light given off by the star is unusual and full of emission lines. This is not too unusual for red giants, but Arcturus has a particularly bad case of the phenomenon. It is 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 than of the Sun.

According to the Hipparcos satellite, Arcturus is 36.7 light years (11.3 parsecs) from Earth, relatively close by in astronomical terms. From this satellite's observations, 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.

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.

The name of the star derives from ancient GreekThe Greek language ( /Elini'k{/) is an Indo-European language which has existed from around the 14th century BC in the Cretan inscriptions called Linear B. Mycenaean Greek of this period is distinguished from later Classical or Ancient Greek of the 8th ce Arktouros and means "Bear Guard". This is a reference to it being the brightest star in the constellation Boötes, the Hunter, which is next to the Big and Little Bears, Ursa MajorUrsa Major is a constellation visible throughout the year in the northern hemisphere. Its name means Great Bear in Latin, and is derived from the legend of Callisto. Its seven brightest stars form a famous asterism known in North America as the Big Dipper and Ursa MinorUrsa Minor is a constellation in the northern sky, the name of which means "Smaller Bear" in Latin. It is one of the 88 modern constellations, and was also one of the 48 listed by Ptolemy. It is notable as the location of the north celestial pole, althoug.

Pre-historic Polynesian navigatorsThis article concerns navigation in the sense of determination of position and direction on the surface of the Earth. See Navigation (disambiguation) for other meanings. There are several traditions of navigation . Polynesian navigation The Polynesian nav knew Arcturus as Hokule'aHokule‘a is a full-scale replica of a wooden sailing vessel used in ancient Hawai'i. Its name means "star of gladness" in Hawaiian, and the name refers to the star Arcturus, which falls directly overhead at Hawai‘i's latitude. It was built in 1975 by the, the "Star of Joy". Arcturus is the zenith star of the Hawaiian IslandsThe Hawaiian Islands are an archipelago of numerous islands and atolls trending northwest by southeast in the North Pacific Ocean between latitudes 19° N and 29° N. The archipelago takes as its name that of the largest island in the group. It extends some. Using Hokule'a and other stars, the Polynesians launched their double-hulled canoeA canoe is a relatively small human-powered boat. It is propelled by one or more people (depending on the size of canoe), using single-bladed paddles. The paddlers face in the direction of travel, either in a seated position or kneeling on the bottom of ts from 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.

Arcturus is mentioned by name in the Bible, in Job 38:32.

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.