Measuring Light Years: How Far Is the Andromeda Galaxy?

[JustATheory]

I was reading up on the Andromeda Galaxy and it was saying that it was 2.2 to 3 million light years away from earth. So my question is how do we measure how far it is in light years?

 

[Drakkith]

Read this article: http://en.wikipedia.org/wiki/Cosmic_distance_ladder

 

[JustATheory]

Awesome thank you!

 

[Chronos]

In fact, Cepheids were used to establish the fact that galaxies other than the Milky Way actually existed in the universe! re: http://hubblesite.org/newscenter/archive/releases/2011/15