Editing Variable star (section)

===Eclipsing binaries===
{{Main|Binary star#Eclipsing binaries}}
[[Image:Light curve of binary star Kepler-16.jpg|right|thumb|upright=1.4|How [[eclipsing binaries]] vary in brightness]]

Extrinsic variables have variations in their brightness, as seen by terrestrial observers, due to some external source. One of the most common reasons for this is the presence of a binary companion star, so that the two together form a [[binary star]]. When seen from certain angles, one star may [[eclipse]] the other, causing a reduction in brightness. One of the most famous eclipsing binaries is [[Algol]], or Beta Persei (β Per).

====Algol variables====
{{Main|Algol variable}}

Algol variables undergo eclipses with one or two minima separated by periods of nearly constant light. The prototype of this class is [[Algol]] in the [[constellation]] [[Perseus (constellation)|Perseus]].

====Double Periodic variables====
{{Main|Double periodic variable}}
Double periodic variables exhibit cyclical mass exchange which causes the orbital period to vary predictably over a very long period. The best known example is [[V393 Scorpii]].

====Beta Lyrae variables====
{{Main|Beta Lyrae variable}}

Beta Lyrae (β Lyr) variables are extremely close binaries, named after the star [[Beta Lyrae|Sheliak]]. The light curves of this class of eclipsing variables are constantly changing, making it almost impossible to determine the exact onset and end of each eclipse.

====W Serpentis variables====
W Serpentis is the prototype of a class of semi-detached binaries including a giant or supergiant transferring material to a massive more compact star. They are characterised, and distinguished from the similar β Lyr systems, by strong UV emission from accretions hotspots on a disc of material.

====W Ursae Majoris variables====
{{Main|W Ursae Majoris variable}}

The stars in this group show periods of less than a day. The stars are so closely situated to each other that their surfaces are almost in contact with each other.