In 1924,Edwin Hubble proved that the Andromeda Galaxy lay far beyond the bounds of the Milky Way,thus putting to rest the idea that it might have been a cloud within our own galaxy.How was he able to prove this?
A)He proved this by observing individual Cepheid variable stars in Andromeda and applying the period-luminosity relation.
B)He was able to measure the parallax of the Andromeda Galaxy.
C)He found that the universe is expanding,and therefore concluded that Andromeda must lie outside our own galaxy.
D)He was the first person ever to look through a telescope at the object we now call the Andromeda Galaxy.

Question

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Edwin Hubble was able to prove that the Andromeda Galaxy lay beyond the Milky Way by observing individual Cepheid variable stars in Andromeda and applying the period-luminosity relation. This allowed him to determine its distance from Earth and prove that it was not a cloud within our own galaxy.

In 1924,Edwin Hubble Proved That the Andromeda Galaxy Lay Far