Spiral Nebula
"Spiral nebula" is an old term for a spiral galaxy. Until the early 20th century, most astronomers believed that objects like the Whirlpool Galaxy were just one more form of nebula that were within our own Milky Way galaxy. The idea that they might instead be other galaxies, independent of the Milky Way, was the subject of the Great Debate of 1920, between Heber Curtis of Lick Observatory and Harlow Shapley of Mt. Wilson Observatory. In 1926, Edwin Hubble observed Cepheid variables in several spiral nebulae, including the Andromeda Galaxy, proving that they are, in fact, entire galaxies outside our own. The term "spiral nebula" has since fallen into disuse.
Read more about this topic: Spiral Galaxy
Famous quotes containing the word spiral:
“Year after year beheld the silent toil
That spread his lustrous coil;
Still as the spiral grew,
He left the past year’s dwelling for the new,
Stole with soft step its shining archway through,
Built up its idle door,
Stretched in his last-found home, and knew the old no more.”
—Oliver Wendell Holmes, Sr. (1809–1894)