A red dwarf is the smallest and coolest kind of star on the Main Sequence. Red dwarfs are by far the most common type of star in the Milky Way, at least in the neighbourhood of the Sun, but because of their low luminosity, individual red dwarfs cannot be easily observed. From Earth, not one that fits the stricter definitions of a red dwarf is visible to the naked eye. Proxima Centauri, the nearest star to the Sun, is a red dwarf, as are fifty of the sixty nearest stars. According to some estimates, red dwarfs make up three-quarters of the stars in the Milky Way.