A Cepheid variable is observed in a distant galaxy. The period of its brightness variations is found to be 10 days. What will astronomers use this observation to determine about the galaxy?
Astronomers will use this observation to determine the distance to the galaxy. Cepheid variables have a well-known relationship between their period of brightness variations and their intrinsic luminosity. By measuring the period of the Cepheid variable in the distant galaxy, astronomers can use this relationship to calculate the absolute magnitude of the star. By comparing this absolute magnitude to the apparent magnitude observed from Earth, astronomers can then determine the distance to the galaxy using methods such as the distance modulus equation.
