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The Andromeda Galaxy
Copyright NOAO/AURA/NSF

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 more than 80 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.