Procyon is the seventh brightest star in the night sky. It is also one of the nearest stars to the solar system, at only 11.41 light years distant. It is located in the constellation Canis Minor. Like many stars, Procyon is part of a binary system which includes Procyon A and Procyon B. Procyon B is a small white dwarf star similar in size to the Earth (~8600 km diameter), but with half the mass of the Sun.
Procyon A itself is a white star with 1.5 times the mass of the Sun, twice the diameter, and 7 times the luminosity. Its companion Procyon B orbits at a distance similar to that between the Sun and Uranus. Like many other binaries, its existence was inferred by astrometric data decades before it was confirmed visually. Astronomers knew its orbit in 1861, but didn't observe it until 1896.
Procyon is a subgiant star, meaning that it has fused most of the hydrogen in its core into helium, and is quickly building up an inert helium center. This helium center will strongly compress the hydrogen above it due to its immense gravity, causing it to fuse faster and for the star to grow into a red giant. Halfway in its transformation between a main sequence star and a giant star, Procyon is referred to as a subgiant. In 10-100 million years, a relatively short amount of time by astrophysics standards, it will swell to become a red giant, much like our Sun is scheduled to do in five billion years.
Because of its closeness, Procyon has been a subject of study in the newly emerging field of asteroseismology. Efforts have been made to observe oscillations in the star's brightness, such as those experienced by our Sun, but as of yet these efforts have not been successful — the star shines at a very steady rate. These findings have challenged some of the prevailing theory of stellar oscillations.
