A type of eclipsing binary with a period of less than 1 day; abbr. EW. The system is a contact binary, with ellipsoidal components, generally of spectral type F–G (or later). Light variation is continuous throughout the orbit, such that the beginning and end of eclipses cannot be defined. Primary and secondary minima are usually of similar amplitude, which is normally below 0.8 mag. W Ursae Majoris itself varies between magnitudes 7.8 and 8.5 every 8 hours.