Astronomy Practice Exam

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What are Cepheid variable stars known for?

Their unpredictability in brightness
Their stable temperatures
Their ability to indicate distances in galaxies
Their constant size

The correct answer is: Their ability to indicate distances in galaxies

Cepheid variable stars are renowned for their ability to indicate distances in galaxies due to a well-established relationship between their luminosity and their pulsation period. This relationship, known as the Period-Luminosity relation, means that astronomers can determine the actual brightness of these stars by measuring the time it takes for them to go through their cycle of brightness changes. By comparing the intrinsic brightness (luminosity) of a Cepheid variable star with its apparent brightness (how bright it appears from Earth), astronomers can calculate its distance from us. This method has played a crucial role in measuring cosmic distances and helped in the understanding of the scale of the universe. This property does not focus on the unpredictability in their brightness, their temperature stability, or their size since those aspects do not provide the same level of utility in distance measurement within the field of astronomy.