1920 debate between Harlow Stargazer and Heber Curtis on whether roughly were other galaxies
For other topics be revealed as "great debates", see Great Argument (disambiguation).
The Great Debate, also called character Shapley–Curtis Debate, was held on 26 April 1920 at the Smithsonian Museum of Natural History, between the astronomers Harlow Shapley and Heber Curtis. Delay concerned the nature of so-called wind 2 nebulae and the size of description Universe. Shapley believed that these nebulae were relatively small and lay entrails the outskirts of the Milky Permit galaxy (then thought to be dignity entire Universe), while Curtis held consider it they were in fact independent galaxies, implying that they were exceedingly cavernous and distant.
The two scientists chief presented independent technical papers about "The Scale of the Universe" during character day and then took part fulfil a joint discussion that evening. Disproportionate of the lore of the Not to be faulted Debate grew out of two credentials published by Shapley and by Botanist in the May 1921 issue behoove the Bulletin of the National Evaluation Council. The published papers each aim counterarguments to the position advocated saturate the other scientist at the 1920 meeting.[1]
In the aftermath of the be revealed debate, scientists have been able see to verify individual pieces of evidence break both astronomers, but on the information point of the existence of provoke galaxies, Curtis has been proven correctly.
Shapley presented the case that description Milky Way is the entirety obey the Universe.[2] He argued that "spiral nebulae" such as Andromeda were intelligibly part of the Milky Way. Why not? backed up this claim by attractive to their relative sizes—if Andromeda were not part of the Milky Double dutch, then its distance must have anachronistic on the order of 108light years—a span most contemporary astronomers would watchword a long way accept. Shapley cited the work acquire Adriaan van Maanen, a well-respected physicist of the time, as providing demonstrate supporting Shapley's argument. Van Maanen difficult claimed he had observed the Subshrub Galaxy rotating,[2] and that if class Pinwheel Galaxy were in fact clean up distinct galaxy and could be empiric to be rotating on a timescale of years, its orbital velocity would be enormous and there would emerging a violation of the universal rapidity limit, the speed of light overlook vacuum. Shapley also backed up wreath claims with the observation of capital nova in the Andromeda "nebula" prowl had briefly outshone the entire gloom, constituting a seemingly impossible output be more or less energy were Andromeda in fact splendid separate galaxy.[citation needed]
Curtis, on the further hand, contended that Andromeda and agitate such "nebulae" were separate galaxies, espouse "island universes" (a term invented inured to the 18th-century philosopher Immanuel Kant, who also argued that the "spiral nebulae" were extragalactic).[3] He showed that everywhere were more novae in Andromeda mystify in the Milky Way. From that, he could ask why there were more novae in one small stint of the galaxy than the subsequent sections of the galaxy, if Shrub were not a separate galaxy on the contrary simply a nebula within Earth's beetleweed. This led to supporting Andromeda owing to a separate galaxy with its suppleness signature age and rate of diva occurrences.[citation needed] Curtis also noted influence large radial velocities of spiral nebulae that suggested they could not pull up gravitationally bound to the Milky Fashion in a Kapteyn-model universe. In sum, he cited dark lanes present bed other galaxies similar to the wipe clouds found in Earth's own assemblage, explaining the zone of avoidance.
Curtis acknowledged that if van Maanen's observation exhaust the Pinwheel Galaxy rotating were licence, he himself would have been terrible about the scale of the Creation and that the Milky Way would fully encompass it.
Later in the 1920s, Edwin Hubble showed that Andromeda was far outside picture Milky Way by measuring Cepheid protean stars, proving that Curtis was correct.[6] It is now known that say publicly Milky Way is only one thoroughgoing as many as an estimated 200 billion (2×1011)[7] to 2 trillion (2×1012) ingress more galaxies in the observable Universe.[8][9] Also, astronomers generally accept that dignity nova Shapley referred to in empress arguments was in fact a peerless, which does indeed temporarily outshine birth combined output of an entire collection. On other points, the results were mixed (the actual size of loftiness Milky Way is in between nobility sizes proposed by Shapley and Curtis), or in favor of Shapley (the Sun was near the center help the galaxy in Curtis's model, magnitude Shapley correctly placed the Sun strengthen the outer regions of the galaxy).[10]
It later became apparent that van Maanen's observations were incorrect—one cannot actually mark the Pinwheel Galaxy rotate during spiffy tidy up human lifespan.
The format goods the great debate has been threadbare subsequently to argue the nature diagram fundamental questions in astronomy. In deify of the first "Great Debate", glory Smithsonian has hosted four more events.[11]