Arcturus

:This article is about the star. For a musical ensemble, see Arcturus (band).

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:For the Arcturus guild on the European Shadowsong server, see World of Warcraft

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Arcturus (α Boo / α Bo?tis / Alpha Bo?tis) is the brightest star in the constellation Bo?tes, and the third brightest star in the sky, with a visual magnitude of −0.05, after Sirius and Canopus. It is the second brightest star visible from northern latitudes and the brightest star in the northern celestial hemisphere.

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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.

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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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Alpha: The first letter of the Greek alphabet, Α α, also has some cultural meanings; see alpha (letter)....

Constellation: A constellation is a group of stars visibly related to each other in a particular configuration. In three-dimensional space, most of the stars we see have little relation to one another, but can appear to be grouped on the celestial sphere of the night sky. Humans excel at finding patterns and throu...

Visual magnitude: REDIRECT Apparent magnitude...