A light curve is a graph showing the way in which the brightness of an object, such as a variable star, changes with time. The light variations may be due to intrinsic changes in the source, as in the case of Cepheid variables, or eclipses, when one member of a binary star system passes in front of the other. Modern techniques in photometry enable even the tiny fluctuations in the light received from a star by the transit of an orbiting planet to be detected.