Galaxies
At the turn of the 20th Century, a great debate was raging in
astronomy. The debate concerned faint, fuzzy objects called "nebulae."
Some astronomers believed nebulae were small clusters of stars in our own galaxy.
Others saw some of them as vast, distant collections of stars, some larger than the
Milky Way itself.
Finally, in 1924, American astronomer Edwin Hubble measured the distance
to what was then called the Andromeda Nebula. He found it to lie
over 2 million light
years from Earth. It was the first object to be recognized as
another galaxy.
Hubble's discovery totally changed our view of the universe. The
already vast distances between stars were dwarfed by the incomprehensible
distances between galaxies. The universe was suddenly a much larger
place than anyone had ever imagined.
The Sloan Digital Sky Survey has found nearly 50 million galaxies so far. In this lesson, you will learn about those galaxies: how to
classify them, what their important characteristics are, and how
scientists think they evolve.
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