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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