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 (-5[1])“kappa mechanism.” (10[2])The Hubble (10[1])constant was initially derived (10[1])from (10[1])observations (10[1])of these stars (10[2]-5[1])in spiral galaxies, (10[3])utilizing a linear relation between “M-sub-V” and “log P.” These standard candles (10[1])are commonly (10[1])used to calibrate distances to type Ia (“one-A”) supernovae (-5[1])and satisfy (10[1])a period-luminosity relation discovered by Henrietta Swan Leavitt. (-5[1])For 10 points, name these variable stars. ■END■ (10[5]0[4])