|watt||A unit of power (energy per unit time).|
|wavelength||The spacing of the crests or troughs in a wave.|
|weak nuclear force or weak interaction||The nuclear force involved in radioactive decay. The weak force is characterized by the slow rate of certain nuclear reactions-such as the decay of the neutron, which occurs with a half-life of 11 min.|
A star that has exhausted most or all of its nuclear fuel and has collapsed to a very small size; such a star is near its final stage of life.
|Wien's law||Formula that relates the temperature of a black-body to the wavelength at which it emits the greatest intensity of radiation.|
|winter solstice||Point on the celestial sphere where the Sun reaches its greatest distance south of the celestial equator; the time of the year with the shortest amount of daylight.|
|Wolf-Rayet star||One of a class of very hot stars that eject shells of gas at very high velocity.|