In The Constellation of Boötes
Arcturus , also designated Alpha Boötis is a star in the constellation of Boötes. It is relatively close at 36.7 light-years from the Sun. Together with Spica and Denebola (or Regulus, depending on the source), Arcturus is part of the Spring Triangle asterism and, by extension, also of the Great Diamond along with the star Cor Caroli.
With an apparent visual magnitude of -0.05, Arcturus is the brightest star in the Northern celestial hemisphere and the fourth-brightest star in the night sky,after Sirius (-1.46 apparent magnitude), Canopus (-0.86) and Alpha Centauri (-0.27). However, Alpha Centauri is a binary star, whose unresolved components to the naked eye are both fainter than Arcturus.
This makes Arcturus the third-brightest individual star, just ahead of Alpha Centauri A, whose apparent magnitude is -0.01. The French mathematician and astronomer Jean-Baptiste Morin observed Arcturus in the daytime with a telescope (a first for any star other than the Sun and supernovae) in 1635, and Arcturus has been seen at or just before sunset with the naked eye.
Arcturus is visible from both Earth's hemispheres as it is located 19° north of the celestial equator. The star culminates at midnight on 27 April, and at 9PM on June 10 being visible during the late northern spring or the southern autumn.
From the northern hemisphere, an easy way to find Arcturus is to follow the arc of the handle of the Big Dipper (Saucepan). By continuing in this path, one can find Spica, "Arc to Arcturus, then spike to Spica".
Ptolemy described Arcturus as subrufa ("slightly red"): it has a B-V color index of +1.23, roughly midway between Pollux (B-V +1.00) and Aldebaran (B-V +1.54).
Eta Boötis, or Muphrid, is only 3.3 light-years distant from Arcturus, and would have a visual magnitude -2.5, whereas an observer on the former system would find Arcturus as bright as Venus as seen from Earth.