アークトゥルス

An orange K-type star, Arcturus shows the ruddy tint recorded in its comparatively high B–V colour index of 1.239. It is the brightest star of the constellation Boötes, listed as Alpha Boötis, and at apparent magnitude −0.05 it stands among the leading lights of the northern spring sky. The star lies 36.7 light-years away, close enough that its absolute magnitude of −0.31 differs little from how it appears from Earth. A northern declination of +19° makes Arcturus a familiar sight across both hemispheres. Its cool orange colour distinguishes it sharply from the blue-white and white stars that dominate the roster of first-magnitude objects.