A Cepheid variable is observed in a galaxy 1 Mpc distant. Its apparent magnitude of 19.8 corresponds to a brightness ratio of b/b_Ÿ = 2.35 x 10^-19. What is its period?

Question

Quizplus · Accepted Answer

The period-luminosity relation for Cepheid variables allows us to determine the period from the apparent magnitude and distance. Given the apparent magnitude and distance, we can calculate the absolute magnitude and use the period-luminosity relation to find that a period of 30 days corresponds to the given brightness ratio.

A Cepheid Variable Is Observed in a Galaxy 1 Mpc