More Information about M31 (the Andromeda Galaxy)
Credit: Public Domain
The Andromeda galaxy can be seen with the naked eye in the
constellation of Andromeda. It looks like a bright cookie in the sky
several degrees across. In the sense that one does not need an
optical aid to see it, one could say that the earliest people to
look up at the night sky "discovered" it.
In terms of when it was realized that it is a galaxy, and
in fact that there are such things as galaxies, each "island
universes" in and of themselves, that was only about 50 to 60
yrs ago. Up until that time, telescopes were not powerful
enough to be able to discern individual stars in galaxies
outside our own, so the objects which we now know to be galaxies
were referred to as "nebulae" - or bright gas clouds. In the early
1920s there was a debate between Curtis and Shapley - two
famous astronomers of the day - as to the nature of the "nebulae".
Curtis argued for the island universe interpretation whereby
each nebula is a galaxy consisting of many individual stars;
Shapley argued the traditional view - namely that all that exists
in the Universe is within a few thousand light years of us,
and our galaxy IS the Universe. Although Shapley was generally
acknowledged to be the "winner" of the debate by virtue of
having more correct and supportable arguments, Curtis turned
out to be right in the end.
The Andromeda galaxy is about 2 million light years from Earth.
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