Proxima Centauri is a red dwarf star with a mass about an eighth of the Sun’s mass (M☉), and average density about 33 times that of the Sun. Because of Proxima Centauri’s proximity to Earth, its angular diameter can be measured directly as about one-seventh the diameter of the Sun. Although it has a very low average luminosity, Proxima is a flare star that undergoes random dramatic increases in brightness because of magnetic activity. The star’s magnetic field is created by convection throughout the stellar body, and the resulting flare activity generates a total X-ray emission similar to that produced by the Sun. The mixing of the fuel at Proxima Centauri’s core through convection and its relatively low energy-production rate mean that it will be a main-sequence star for another four trillion years.