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Dr. Edwin Hubble: Study of Extragalactic Nebulae, 1939

An Important Question

In 1919, when Edwin Hubble first began his work in the field of astronomy, there was an ongoing debate whether Earth's home, the Milky Way galaxy, made up the whole universe, or whether it was just one of many galaxies inhabiting a much greater space. But without better telescopes, scientists couldn't come to a resolution. Hubble was fortunate enough to conduct his research at Mount Wilson Observatory, using the largest and most powerful telescope in the world.

Hubble's research involved an important question that astronomers hadn't been able to answer up to that point. What are nebulae? Setting his sights on Andromeda Nebula, Hubble was able to detect Cepheid stars within it, and applying Henrietta Leavitt's pioneering work using Cepheid stars as a measure of distance, determined that the Andromeda Cepheids were much too far away to be part of the Milky Way galaxy. He concluded that Andromeda Nebula wasn't a cloud of gas within the Milky Way at all, but rather an "island universe"—an entirely different galaxy. Hubble settled the ongoing debate with his discovery that the Milky Way is but one of millions of galaxies, and forever changed man's view of the universe.


Letter from Edwin Hubble to Dr. Allen, Enclosing a copy of rough draft of address, 5/19/1939 (626k)


Letter from Secretary and Director to Edwin Hubble, Expressing appreciation for participation in Medal Day ceremonies, 5/25/1939 (390k)