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International Year of Astronomy - Edwin Hubble

The Andromeda Galaxy, or M31, is a spiral galaxy approximately 2.5 million light years away. It is one of the nearest large galaxies and one of the farthest objects visible with the unaided eye. R. Gendler
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Edwin Hubble (1889 -

"Equipped with his
five senses, man explores the universe around him and calls the adventure

American astronomer Edwin Powell Hubble worked at Mount
Wilson Observatory in California and is famous for his four groundbreaking
achievements in modern cosmology. 

Up until the early 20th century, it was commonly
believed that the Universe consisted entirely of stars, diffuse nebulae, and
other astronomical bodies within the Milky Way. Hubble observed that the then
called "Andromeda Nebula" was not a cloud-like structure, but was formed of a
great number of individual stars. Among those stars he found a special type
called Cepheid variables-stars whose brightness varies with a predictable
pattern and for which the period of the variation is correlated to each star's
intrinsic luminosity-, which allowed him to accurately measure the distance to
the Andromeda Nebula. Hubble therefore showed that Andromeda was at a much
greater distance than what was previously believed, surely not part of our
galaxy, and in fact was an entirely separate galaxy not unlike the Milky Way.

Hubble devised a galaxy classification scheme (commonly
known as the Hubble Tuning Fork or the Hubble Sequence) based of the different
shapes of the galaxies he observed-ellipticals, spirals, and barred spirals.
Further research on galaxies revealed-as had already been understood by other
scientists of his time-that all galaxies move away from each other. The speed
of this recession between any pair of galaxies is proportional to the distance
between them, so the greater their separation, the faster they move away from
each other. This relation, commonly known as the Hubble Law, implies that the
Universe is expanding and it is one of the main supports of the Big Bag theory. 

Edwin Hubble was widely recognized during his time for his
groundbreaking research in astronomy, but he is probably most famous among the
general public in contemporary times due to the space observatory that bears
his name-the Hubble Space Telescope.

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