Star whose observed brightness varies noticeably in intensity.
Pulsating variables expand and contract in cycles, pulsating rhythmically in brightness and size. Explosive variables include nova s and supernova s, which brighten rapidly due to sudden outbursts of radiant energy; the increased brightness lasts a short time, followed by relatively slow dimming. Eclipsing variable star s are variable only because light from one star is blocked by another in Earth's direction. Hundreds of thousands of variable stars are known. See also binary star ; Cepheid variable ; flare star ; pulsar ; T Tauri star .