The Andromeda Galaxy is one of the most distant objects visible to the naked eye, at over 2 million light years away it appears as a point of light and a faint smudge even in light polluted skies. It's full extent covers the length of 5 full moons in the sky though this would be very difficult to observe unaided. Andromeda is one of the more important objects when it comes to our understanding of the Universe and cosmology. For many years it was named The Spiral Nebula in Andromeda which reflects the fact that it was believed there was only one galaxy, The Milky Way. What we now know to be galaxies were imagined to be nebulae like any other. It wasn't until the early 20th century that their true nature was revealed. In 1908 Henrietta Swan Leavitt demonstrated a direct relationship between the period of a Cepheid type variable star and their absolute luminosity. By using this relationship Edwin Hubble was able to determine the absolute brightness of Cepheid variable stars in Andromeda and by comparing to their apparent brightness, find their distance. This showed that Andromeda and other spiral nebulae were much further away than had even been considered, at a greater distance than any other known objects. Therefore these must be their own galaxies like our Milky Way, in fact Andromeda is slightly larger, containing over 1 trillion stars.
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