WHAT CAUSES VARIABILITY?
Variable stars are classified based on the actual physical mechanism that causes their brightness to vary. Pulsating variables are stars which brighten and dim due to a physical change in their size and surface temperature. We will observe Delta Cephei, which belongs to this class of variable stars. Eclipsing binaries appear to brighten and dim because the light from one star is blocked from view (occulted or eclipsed) by an orbiting companion star. As a result, the light from an eclipsing binary is generally constant except for those brief periods when one star is actually in front of the other. While Algol (the “demon star” in Perseus) is the most famous and easily observed example, Perseus will not be easily visible for us until the end of the Fall semester. Instead, we will observe Beta Lyrae, another naked-eye eclipsing binary.
