Arcturus is a red giant star in the northern constellation of Boötes, and the brightest star in the constellation. It has the Bayer designation α Boötis, which is Latinized to Alpha Boötis and abbreviated Alpha Boo or α Boo. With an apparent visual magnitude of −0.05, it is the fourth-brightest star in the night sky and the brightest in the northern celestial hemisphere. Arcturus forms one corner of the Spring Triangle asterism.