Proxima Centauri is a faint red star a little over 4 light-years from our solar system, and is the closest star to Earth other than the sun. It is classified as a red dwarf, the smallest, dimmest, and longest-lived type of active star. (I say "active" to indicate that it is currently producing energy from nuclear fusion, unlike "dead" stars such as white dwarfs and neutron stars.) It is close to the binary star Alpha Centauri, and might be in orbit around it, but scientists aren't sure whether this is so. With an apparent magnitude of 11, Proxima Centauri is far too dim to see from Earth, and would have a magnitude of 5 if seen from the vicinity of Alpha Centauri. (Magnitudes are indicated numerically in a logarithmic manner. A magnitude 1 star appears 2.51 times as bright as magnitude 2 star, a magnitude 2 star appears 2.51 times as bright as a magnitude 3 star, and so on. Depending on viewing conditions, stars with a magnitude between 5 and 6 are the faintest that can be seen with the unaided eye.)
Today, astronomers have announced that Proxima Centauri has a planet, which would of course be the closest exo-planet to our solar system. It orbits the star every 11 Earth days, and lies within the "Goldilocks zone", in which liquid water may exist. The planet has a mass about 1.3 times that of Earth. Whether is has an atmosphere or even a solid surface has not been determined.
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