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

Question

Quizplus · Accepted Answer

Hubble used the observation of Cepheid variable stars in M31 to determine its distance. Cepheid variables are very luminous stars whose brightness varies in a regular pattern that can be used to determine their distance. This method allowed Hubble to establish the concept of separate and individual galaxies throughout the universe.

The Method Used by Hubble to Determine the Distance to the Andromeda