USA HISTORY

Detailed explanation-1: -At the turn of the last century, a little remembered but dramatic debate took place between prominent astronomers Harlow Shapely and Heber Curtis.

Detailed explanation-2: -Shapley argued that the universe was comprised of a single galaxy, while Curtis held that it contained many galaxies. In holding these positions, each came to different conclusions regarding the celestial objects astronomers at the time called “spiral nebulae, ” the nature of which was still unclear in 1920.

Detailed explanation-3: -After the debate Later in the 1920s, Edwin Hubble showed that Andromeda was far outside the Milky Way by measuring Cepheid variable stars, proving that Curtis was correct.

Detailed explanation-4: -In 1920, there were two competing ideas about the universe. One was that our Milky Way was it, and that everything we saw was in it. The other was that these spiral nebulae seen in the sky were also like our Milky Way, island universes in their own right. Two astronomers debated this controversy in that year.

Detailed explanation-5: -On the other hand, some astronomers argued that these spiral nebulae were “island universes” like the Milky Way, and they were simply so far away that their stars were not resolved into point sources of light but were instead blurred together so they looked like a nebula.