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In 1917, Heber Doust Curtis observed a nova within what then was called the "Andromeda Nebula". Searching the photographic record, 11 more novae were discovered. Curtis noticed that novas in Andromeda were drastically fainter than novas in the Milky Way. Based on this, Curtis was able to estimate that Andromeda was 500,000 light-years away.
The Andromeda Galaxy, for instance, was once referred to as the Andromeda Nebula (and spiral galaxies in general as "spiral nebulae") before the true nature of galaxies was confirmed in the early 20th century by Vesto Slipher, Edwin Hubble, and others. Edwin Hubble discovered that most nebulae are associated with stars and illuminated by starlight.
1750 – Thomas Wright discusses galaxies and the flattened shape of the Milky Way and speculates nebulae as separate. [11] 1755 – Immanuel Kant drawing on Wright's work conjectures that our galaxy is a rotating disk of stars held together by gravity, and that the nebulae are separate such galaxies; he calls them Island Universes.
In astronomy, galactocentrism is the theory that the Milky Way Galaxy, home of Earth ' s Solar System, is at or near the center of the Universe. [1] [2]Thomas Wright and Immanuel Kant first speculated that fuzzy patches of light called nebulae were actually distant "island universes" consisting of many stellar systems. [3]
Hubble proved that many objects previously thought to be clouds of dust and gas and classified as "nebulae" were actually galaxies beyond the Milky Way. [4] He used the strong direct relationship between a classical Cepheid variable 's luminosity and pulsation period [ 5 ] [ 6 ] (discovered in 1908 by Henrietta Swan Leavitt [ 7 ] ) for scaling ...
He waited until 1802 (in Catalogue of 500 new Nebulae, nebulous Stars, planetary Nebulae, and Clusters of Stars; with Remarks on the Construction of the Heavens) to announce the hypothesis that the two stars were "binary sidereal systems" orbiting under mutual gravitational attraction, a hypothesis he confirmed in 1803 in his Account of the ...
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Galaxies were initially discovered telescopically and were known as spiral nebulae. Most 18th- to 19th-century astronomers considered them as either unresolved star clusters or extragalactic nebulae, [ citation needed ] and were just thought of as a part of the Milky Way, but their true composition and natures remained a mystery.