The observational fact about a Cepheid variable star that leads to a measurement of its distance from Earth is that its period of variation is directly related to its
A) absolute magnitude or luminosity.
B) apparent magnitude.
C) speed away from us,using the relativistic effect upon pulsation period.
D) surface temperature.

Question

Quizplus · Accepted Answer

The period of variation of a Cepheid variable star is directly related to its absolute magnitude or luminosity. Therefore, by measuring its period of variation, astronomers can determine its absolute magnitude, which can then be compared to its apparent magnitude (as observed from Earth) to calculate its distance using the inverse square law of brightness.

The Observational Fact About a Cepheid Variable Star That Leads