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:
“What is art,
But life upon the larger scale, the higher,
When, graduating up in a spiral line
Of still expanding and ascending gyres,
It pushes toward the intense significance
Of all things, hungry for the Infinite?
Art’s life,—and where we live, we suffer and toil.”
—Elizabeth Barrett Browning (1806–1861)