in astronomy, graph of the changes in brightness with time of a star, particularly of the variable type. The light curves of different kinds of variable stars differ in the degree of change in magnitude (i.e., the amount of light flux observed), in the degree of regularity from one cycle to the next, and in the length of the cycle—i.e., the period. Variations in magnitude range from barely detectable for a star that is eclipsed by a planet in orbit around it to the billion fold increase in brightness of a supernova, while periods vary from milliseconds for some pulsars to a supernova's single explosion.