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"On This Day" In Engineering History

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December 30, 1924 – Beyond the Milky Way

Posted December 30, 2009 10:05 AM by Steve Melito

On this day in engineering history, the American astronomer Edwin Hubble discovered the existence of "island universes" beyond Earth's Milky Way galaxy. A man of many talents, Hubble had studied mathematics at Chicago and jurisprudence at Oxford before abandoning a budding legal career to turn his attentions skyward. In 1919, the former heavyweight boxer and U.S. Army Major joined California's Mount Wilson Observatory after earning a doctorate in astronomy. Five years later, Edwin Hubble made an amazing discovery using the 100-inch Hooker telescope, then the world's largest.

The Spiral Nebulae

For years, astronomers had debated whether the spiral nebulae were "island universes" (i.e. other galaxies) or "lesser systems tributary to the Galaxy". In 1906, George Ellery Hale, founder of the Mount Wilson Observatory, had theorized that the Andromeda Nebulae had a spectrum similar to that of the Sun. Photographs from the facility's 60-inch telescope showed "star-like condensations" that, as scientists would later learn, represented the first images of stars in other galaxies. Although a definitive answer to the celestial debate awaited Edwin Hubble's 1924 discovery, proponents of multiple galaxies cited the presence of interstellar material through the absorption of blue light from other galaxies.

Leaning on Leavitt

Using the Mount Wilson Observatory's 100-inch telescope, Edwin Hubble discovered a Cepheid, or variable star, in the Andromeda Nebulae on December 30, 1924. Thanks to Henrietta Leavitt, a Harvard College astronomer who had discovered the Cepheid variable-period luminosity relationship, Hubble studied the time the star took to go from bright to dim and then calculated that the Cepheid was too distant to be part of the Milky Way galaxy. In an age when many astronomers believed that space consisted of only the Milky Way and the Magellanic Clouds, Hubble announced that the universe was much larger than presumed.

A New Year's Celebration

When Edwin Hubble announced his findings to a meeting of the American Astronomical Society on New Year's Day, 1925, the long debate about multiple galaxies ended. According to Mount Wilson and Las Campanas Observatories staff member Allan Sandage in the Hubble Atlas of Galaxies, Edwin Hubble's discovery with the 100-inch telescope had "proved beyond question that nebulae were external galaxies comparable to our own. It opened the last frontier of astronomy, and gave, for the first time, the correct conceptual value of the universe. Galaxies are the units of matter that define the granular structure of the universe."

Resources

http://www.pbs.org/wgbh/aso/databank/entries/bahubb.html

http://www.mtwilson.edu/his/art/g1a4.php

http://www.pbs.org/wgbh/aso/databank/entries/baleav.html

http://cr4.globalspec.com/blogentry/9990

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