Henrietta Leavitt was a human computer hired but the Harvard Observatory in the 1890s who figured out how to calculate star-distance, helping us understand how large the universe really is.

via Vox

It’s the same here on Earth. Imagine you’re on the beach at night and see two lighthouse lights glowing in the distance, but one seems brighter than the other. If you knew both lighthouses used the same lightbulb, you could conclude that the dimmer light is farther away. But it’s also possible that the dimmer light just comes from a lower-wattage lightbulb, perhaps nearer to you.

Scientists needed a way to find out the intrinsic brightness of stars — to figure out their wattage, so to speak. That’s when Henrietta Leavitt, a Massachusetts-born “computer” who worked at the Harvard College Observatory, came along. In 1908, she published a discovery that may sound small but is one of the most important in the history of astronomy. It cracked open the universe.

Read more.