Friedrich Argelander developed a system for naming these objects. The compression of layers of gas in these objects increases their opacity, according to the Eddington Valve mechanism. Henrietta Leavitt studied thousands of these objects in the Magellanic Clouds and derived a period-luminosity relationship for them. These stars, which come in intrinsic and extrinsic types, can be classified into types such as RR Lyrae, Mira, and Cepheid. For 10 points, name this class of stars whose brightness regularly fluctuates, as seen from Earth.
a) Pulsars
b) Quasars
c) Variable stars
d) Neutron stars