Here’s a nice graphic summary of one of the great advances of science (in particular, astronomy) in the past century.
Vox: How scientists discovered the universe is really freaking huge, subtitled, Edwin Hubble’s name is everywhere in astronomy. Henrietta Leavitt’s should be too.
It’s a podcast, which I haven’t listened to (I never have time for podcasts) with Brian Resnick and others, but it’s also a series of graphics and texts about Henrietta Leavitt, a “computer” back in the days when the term referred to people (usually women) who did calculations. Hers was a first step in a series of discoveries about the size of our universe.
Most stars are too far away to distance by parallax. Leavitt discovered that Cepheid variables, whose variable pulses were directly correlated with brightness, could be used to establish their distance. Thus by the length of pulses, she determined how far away they were, including some in the Magellanic Clouds– now known to be small galaxies outside of our own, the Milky Way.
This resolved a debate about observations by Edwin Hubble that led to conclusions that other nebulous patches in the sky, like the Andromeda “Nebula” (visible to the naked eye), were actually separate galaxies apart from the Milky Way. And millions of light years away.
Scientists kept building on Leavitt’s ruler to measure the universe. And as they used these measuring tools, their understanding of the universe evolved. They realized it was far bigger than previously thought, there are billions of galaxies, and it’s expanding: Those galaxies are moving further and further away from one another.
Astronomers also realized that the universe had a beginning. If galaxies are moving away from one another now, it means they were closer together in the past — which led scientists to the idea of the Big Bang.