The method Hubble used to determine the distance to the Andromeda Galaxy (M31), thereby establishing the concept of separate and individual galaxies throughout the universe, was the
A) observation of Cepheid variable stars.
B) measurement of the redshift of the whole galaxy.
C) measurement of stellar parallax, or apparent motion, of stars because of Earth's orbital motion.
D) observation of the brightnesses of novae.

Question

Quizplus · Accepted Answer

Hubble used the observation of Cepheid variable stars in the Andromeda Galaxy to determine its distance. Cepheid variables have a well-defined relationship between their luminosity and pulsation period, allowing astronomers to use them as "standard candles" for measuring astronomical distances. This method showed that Andromeda was far outside the Milky Way, leading to the realization that it was a separate galaxy and that the universe contained many galaxies.

The Method Hubble Used to Determine the Distance to the Andromeda