The observation by Hubble that demonstrated for the first time that the Andromeda "nebula" was at a very large distance from the Sun,and outside our Galaxy,was that
A) the "nebula" appeared to be rotating night-by-night around a center that was not the center of our Galaxy.
B) Cepheid variable stars appeared to be very faint in the "nebula."
C) stars with characteristics similar to those of our Sun appeared to be absent in this "nebula."
D) globular clusters appeared to be distributed in a halo around the "nebula," a sure sign of a separate galaxy.

Question

Quizplus · Accepted Answer

Hubble observed Cepheid variable stars in the Andromeda "nebula" and used their known luminosity-period relationship to calculate their distance. The faintness of these stars indicated that Andromeda was much farther away than previously thought, placing it well outside our own Galaxy.

The Observation by Hubble That Demonstrated for the First Time