The most distant object in space that we can see with our unaided eyes, the Andromeda Galaxy, is located more than 2 million light-years away — but you can see it in the early evening night sky this autumn.
By Joe Rao | SPACE.com
Step outside this week and look high overhead at around 8:30 p.m. local time, and you’ll be able to sight what is without a doubt the most famous galaxy in all of our sky, M31, in the constellation Andromeda — an object that nearly a century ago helped extend our perspective of the cosmos as nothing else has ever done.
As recently as the early 1900s, astronomers quarreled about whether this and other spiral „nebulas“ were part of our own system of stars, which we call the Milky Way, or if they were „island universes“ — that is, independent stellar systems of their own. [Seeing the Best Night-Sky Sights of Autumn Using Mobile Apps]
In an attempt to settle this issue once and for all, on April 26, 1920, two leading astronomers of the day, Harlow Shapley and Heber D. Curtis, squared off at the Smithsonian Museum of Natural History in Washington, D.C., in what has since become known as „The Great Debate.“ At the time, Shapley — who ultimately went on to become one of the 20th century’s greatest extragalactic experts — incorrectly argued that these spiral „nebulas“ were part of our own stellar system. He was led astray by Adriaan Van Maanen, an astronomer working at the Mount Wilson Observatory, who measured the distances of stellar objects using parallax.