Wendy Freedman used infrared measurements to constrain these stars’ Wesenheit (“VESS-en-hite”) function. Observing that an equation concerning these stars depended on “population” prompted Walter Baade to recalculate the size of the known universe (-5[1])to double its previous estimate. (10[1])Arthur (10[1])Eddington proposed (10[1])that compressing these stars’ outer layers causes an increase in opacity, an effect later known as the “kappa mechanism.” The Hubble constant was initially derived from observations (10[1])of these stars (10[2])in spiral galaxies, (10[2])utilizing a linear relation between “M-sub-V” and “log P.” These standard candles are commonly (10[1])used to calibrate distances to type Ia (“one-A”) supernovae (-5[1])and satisfy a period-luminosity relation discovered by Henrietta Swan Leavitt. For 10 points, name these variable stars. ■END■ (10[3]0[3])