Variable Stars

Abstract

The description of stellar evolution given in the previous chapter leads quite naturally to variable stars, because as a star evolves away from the main sequence, it may, if it is massive enough, pass through instability regions in the H-R diagram. In these regions the star’s internal gravitational equilibrium is disturbed and relatively rapid structural changes occur that produce variations in the star’s luminosity. All stars, of course, change slowly as a consequence of their evolutionary development, but these are not the changes we have in mind, for these slow changes occur over hundreds of millions or billions of years. Variable stars are those whose brightness variations can be observed from day to day or hour to hour.

But he, with first a start and then a wink,

Said, “There’s another star gone out, I think.”

—GEORGE GORDON, LORD BYRON, George III