prototype star of the class of Cepheid variables (Cepheid variable), in the constellation Cepheus. Its apparent visual magnitude at minimum is 4.34 and at maximum 3.51, changing in a regular cycle of about five days and nine hours. Its variations in brightness were discovered in 1784 by the English amateur astronomer John Goodricke (Goodricke, John), and periodic changes in radial velocity (now attributed to pulsation) were established in 1894.