Final answer:
Cepheid variables can be used as "standard candles" to measure distances in astronomy. Their period of variation is directly related to their average luminosity, and by comparing their luminosity with their apparent brightness, astronomers can calculate their distances.
Step-by-step explanation:
Cepheid variables are a type of pulsating variable star that can be used as "standard candles" to measure distances in astronomy.
The brightness of cepheid variables varies in a regular repeating pattern, and their period of variation is directly related to their average luminosity. By measuring the period of a cepheid variable and comparing its luminosity with its apparent brightness, astronomers can calculate the star's distance.
For example, the longer the period of a cepheid variable (the longer the star takes to vary), the greater its luminosity. This relationship, known as the period-luminosity relation, allows astronomers to determine the luminosity of a cepheid variable once its period is measured. Then, by comparing the star's luminosity with its apparent brightness as observed from Earth, they can determine the star's distance using the inverse square law of light.