To Get the Distance to a Cepheid Variable Star, Astronomers

Multiple Choice

To get the distance to a Cepheid variable star, astronomers must take several steps. Which of the following is NOT one of these steps?

A) observe the star getting brighter and dimmer to establish that it varies
B) measure the period of variations by timing when the star is brightest and dimmest
C) estimate the apparent brightness of the star
D) measure the star's Doppler shift from its spectrum
E) apply the period-luminosity relationship