A type of eclipsing binary with a light-curve that shows continuous variation throughout the orbital period, which is normally 1 day or more; abbr. EB. A secondary minimum is always observed and is normally much shallower than the primary minimum, which usually has an amplitude of less than 2 mag. Beta Lyrae itself varies between mags. 3.25 and 4.36 in 12.9 days, with a secondary minimum of 3.85. Beta Lyrae systems were once thought to be contact binaries with approximately ellipsoidal components. However, most appear to be semidetached binaries in which there is mass transfer towards the smaller component. In Beta Lyrae itself, a bright giant secondary is rapidly losing mass to what appears to be a main-sequence primary, which is hidden by a thick accretion disk. Energy from the infall of material excites high-temperature emission from a shell of material that surrounds both components and is being lost from the system.