+ Once upon a time we didn't know how far away everything in space was. Without a means of measuring the distance to far away stars there was no way to be sure: Enter Henrietta Swan Leavitt! She discovered that a class of variable stars have an inherent brightness in a ratio to how long it takes to go through their variable cycle. So if we can find two of these stars and compare their brightness and period we can compare the relative distance between to two! Though cock-blocked of recognition in her day, her work is what allowed us to finally measure great distances in space, and eventually led Hubble to determine that the universe is expanding.