● Arcturus Arcturus is a star in Bootes. ### ############# ################### ##################### ####################### ####################### ######################### ####################### ####################### ##################### ################### ############# ### Type Orange giant Constellation Bootes Magnitude -0.0 Spectral type K1.5IIIFe-0.5 Distance 37 light years You need naked eye from a dark sky Known as Bayer α Boo Yale HR 5340 Physical Radius 25 times the Sun More information about Arcturus Arcturus is an old star that has already left the main sequence and swollen to 25 times the Sun's width. It is moving through the galaxy at a steep angle to everything around it, which suggests it arrived with a small galaxy the Milky Way absorbed long ago. Its name is the Greek Ἀρκτοῦρος, "the bear guard", and it earns it by following the Great Bear around the pole. It is one of the very few star names to have come down unchanged from Greek without passing through Arabic on the way. Etymology From Greek Reading Arktouros · Ἀρκτοῦρος Literally bear guard Bayer lettered the stars of each constellation in his Uranometria of 1603, in order of brightness. He was working from Tycho's magnitudes by eye, and the order he recorded is often wrong. First published in 1930 by Yale astronomer Frank Schlesinger, and maintained since, the Yale Bright Star Catalogue lists every star down to magnitude 6.5. It contains 9,110 stars. where it is tonight: skymap.sh/Arcturus