How was Edwin Hubble able to use his discovery of a Cepheid in Andromeda to prove that the "spiral nebulae" were actually entire galaxies?
A)There are no Cepheids in the Milky Way,so his discovery proved that it had to be in another galaxy.
B)He measured the stellar parallax of the Cepheid in Andromeda,was able to determine the distance to it,and showed that it was far outside the Milky Way Galaxy.
C)From the period-luminosity relation for Cepheids,he was able to determine the distance to Andromeda and show that it was far outside the Milky Way Galaxy.
D)Since a Cepheid is a type of luminous galaxy,when he found it in Andromeda he was able to prove that Andromeda was a separate galaxy from the Milky Way.

Question

Quizplus · Accepted Answer

Edwin Hubble was able to use his discovery of a Cepheid in Andromeda to prove that the "spiral nebulae" were actually entire galaxies by using the period-luminosity relation for Cepheids. By observing the period of the Cepheid in Andromeda and comparing it to its apparent brightness, he was able to determine its absolute brightness and therefore its distance from Earth. This distance was much too far to be within the Milky Way Galaxy, proving that Andromeda was a separate galaxy and that the "spiral nebulae" were also separate galaxies.

How Was Edwin Hubble Able to Use His Discovery of a Cepheid