Procyon

Procyon (ˈproʊsi.ɒn) is the brightest star in the constellation of Canis Minor and usually the eighth-brightest star in the night sky, with an apparent visual magnitude of 0.34. It has the Bayer designation α Canis Minoris, which is Latinized to Alpha Canis Minoris, and abbreviated α CMi or Alpha CMi, respectively. As determined by the European Space Agency Hipparcos astrometry satellite, this system lies at a distance of just , and is therefore one of Earth's nearest stellar neighbors. A binary star system, Procyon consists of a white-hued main-sequence star of spectral type F5 IV–V, designated component A, in orbit with a faint white dwarf companion of spectral type DQZ, named Procyon B. The pair orbit each other with a period of 40.84 years and an eccentricity of 0.4. Procyon is usually the eighth-brightest star in the night sky, culminating at midnight on 14 January. It forms one of the three vertices of the Winter Triangle asterism, in combination with Sirius and Betelgeuse. The prime period for evening viewing of Procyon is in late winter in the Northern Hemisphere. It has a color index of 0.42, and its hue has been described as having a faint yellow tinge to it. Procyon is a binary star system with a bright primary component, Procyon A, having an apparent magnitude of 0.34, and a faint companion, Procyon B, at magnitude 10.7. The pair orbit each other with a period of 40.84 years along an elliptical orbit with an eccentricity of 0.4, more eccentric than Mercury's. The plane of their orbit is inclined at an angle of 31.1° to the line of sight with the Earth. The average separation of the two components is 15.0AU, a little less than the distance between Uranus and the Sun, though the eccentric orbit carries them as close as 8.9 AU and as far as 21.0 AU. The primary has a stellar classification of F5IV–V, indicating that it is a late-stage F-type main-sequence star. Procyon A is bright for its spectral class, suggesting that it is evolving into a subgiant that has nearly fused its hydrogen core into helium, after which it will expand as the nuclear reactions move outside the core.