The identification of "spiral nebulae" as large groupings of stars outside of our own galaxy was proven by ____.
A) photographic plates made by Edwin Hubble showing stars and Cepheid variables
B) the results of the Shapley-Curtis debate
C) Immanual Kant's "island universe" theory
D) William Parsons' observation and description of their spiral structure
E) Harlow Shapley's observations of their radio spectrum

Question

Quizplus · Accepted Answer

Edwin Hubble's use of photographic plates to identify Cepheid variables in the Andromeda Nebula was crucial in proving that spiral nebulae are indeed separate galaxies outside of our own Milky Way. This discovery expanded our understanding of the universe significantly.

The Identification of "Spiral Nebulae" as Large Groupings of Stars