 Variable stars have periodic or random changes in luminosity because of intrinsic or extrinsic properties . Of the intrinsically variable stars , the primary types can be subdivided into three principal groups . 
 Variable stars <a href='got' title='1'><mark>have</mark></a> periodic or random changes in luminosity because of intrinsic or extrinsic properties . Of the intrinsically variable stars , the primary types can be subdivided into three principal groups . 
Variable stars got periodic or random changes in luminosity because of intrinsic or extrinsic properties . Of the intrinsically variable stars , da primary types can b subdivided into three principal groups .