Variable stars vary in the intensity of the light they emit. Some physical changes that are
usually related to changes in brightness are changes in size, mass, colour, and/or
Variable stars are grouped into three categories: the pulsating (expanding and
contracting, causing them to change their brightness and size) variables, the eruptive
(sudden outbursts of radiant energy, which causes rapid brightening) variables, and the
eclipsing (partially blocks the light of another star as it passes in front of it)
The pulsating and eruptive variables are both intristic variables because the stars
change physically, whereas the eclipsing variables are extrinsic because the change is
caused by two stars, neither physically changing.
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