Edwin Hubble
Is the universe standing still?
That time, that place
Mount Wilson held the hundred-inch telescope, the largest in the world.
And astronomy had a dispute it could not settle: are the faint spiral shapes in the sky clouds of gas inside our galaxy, or other galaxies beyond it?
With no way to measure their distance, there was no way to decide.
Why this question
Comparing plate after plate of the Andromeda nebula, Hubble found within it a star varying periodically in brightness.
Leavitt's ruler could now be used: measure the period to get the true brightness, compare with apparent brightness, and the distance follows.
What was found
The distance came out several times the size of our own galaxy. Andromeda was not inside it.
Our galaxy was not the universe but one among a multitude.
And what followed was larger. Analyzing the light of many galaxies, he found that nearly all their spectra were shifted toward the red — they were receding. Moreover, the farther away, the faster.
The universe was growing.
Our galaxy was the universe, and the universe was unchanging
A variable star found in Andromeda, and redshift growing with distance
Einstein had inserted a constant into his equations to keep the universe static, and called it his greatest blunder. Curiously, that constant returned at the end of the century as dark energy