When my grandmother was an adult...

...she didn't know that there were billions of galaxies.

According to Io9:

This star may not look like much, but in 1923 it changed our understanding of the universe forever. It showed us that the Milky Way wasn't a lonely island universe, but instead just one of billions and billions of galaxies.


It seems weird to think that less than a hundred years ago we still had no idea that other galaxies existed. While humanity had long since realized that the Earth revolved around the Sun - and in turn that the Sun revolved around the center of the Milky Way - astronomers still clung to the last vestiges of the ancient notion that we were at the center of the universe. In this case, that meant that our galaxy was the universe, meaning the entire cosmos was just this one vast collection of stars.

Our nearest major galactic neighbor is Andromeda, which in the early 1900s most astronomers just considered a "spiral nebula." This meant it was a blurry patch of light and nobody was quite sure what it was, but it was most assuredly inside our galaxy. At least, that was the orthodox view, but astronomers like Edwin Hubble weren't so sure. And that's when the discovery of this star, today known simply as Hubble variable number one, was so crucial.

A Cepheid variable star is one that brightens and dims in a predictable pattern, and by 1923 variable stars were already well established as a very reliable way to judge astronomical distances. When Hubble calculated the distance of star V1, he changed cosmology forever. The star was unquestionably outside our own galaxy and located far away in that of the Andromeda galaxy. And so the universe once again grew larger in the eyes of astronomers, and we more or less entered the modern age of cosmology.

I wonder what it was like for people to adjust to the idea that the Earth went around the sun, but that transformation is buried in history, back in the days of my great-to-the-15th-grandparents.  

But what it was like to go through the mental transformation involving the idea that our world is only a part of a galaxy that itself is only one out of billions of galaxies was something that I could have asked about, if I had only known to ask.