Arcturus

Brightest star in the constellation Boötes and the fourth-brightest star in the night sky. Arcturus is a red giant about 28 times larger than the Sun and 70 times more luminous, 36 light years away from the Sun.

Its name is derived from the Greek and signifies ‘the Guardian of the Bear’. As the brightest star in the north celestial hemisphere it must always have been conspicuous, but some of the ancient literary references to it, such as those in the biblical Book of Job, are probably intended to include the Great Bear as well.

Arcturus was the first star for which a proper motion was detected. Edmond Halley in 1718 noticed that, relatively to the surrounding stars, it had moved by about one degree from the position recorded by the Greek astronomer Ptolemy (2nd century AD) in the Almagest.