Henrietta Swan Leavitt

Hello! My name is Henrietta Swan Leavitt. I was born on a day full of fireworks, July 4th, in the year 1868. Even as a little girl, I loved the biggest firework show of all: the night sky! I would stare up at the twinkling stars and wonder what they were and how far away they could be. I loved learning so much that I went to college, which was something not many women did back then. I studied everything I could, but the stars were always my favorite.

After I finished school in 1892, I got a very special job. In 1893, I started working at a famous place called the Harvard College Observatory. But I wasn't looking through the giant telescopes. In those days, that was a job for men. Instead, I was a 'computer.' That didn't mean I was a machine! It meant my job was to look very closely at pictures of the stars that were taken on big glass plates. My friends and I would sit in a room all day, measuring and counting the tiny specks of light. It was like being a detective for the stars!

While I was looking at my star pictures, I noticed some very special stars. They weren't just shining—they were blinking! They would get brighter, then dimmer, then brighter again, like a slow, steady heartbeat. These were called Cepheid variable stars. I studied them for a long, long time. Then, in 1908, I found a secret pattern! The really big, bright stars blinked very slowly. The smaller, dimmer stars blinked much faster. This was a huge discovery! It meant that if you knew how fast a star was blinking, you could figure out how bright it truly was, and that could help you figure out how far away it was. It was like I had found a ruler to measure the whole universe!

My discovery helped other astronomers make even bigger discoveries. They used my 'star ruler' to prove that our galaxy, the Milky Way, is just one of many, many galaxies in the giant universe. I lived to be 53 years old. Even though I became deaf and couldn't hear the world around me very well, I felt like I could hear the stars singing. Today, people remember me as the woman who gave us a way to measure the heavens. The next time you look up at the night sky, I hope you'll remember that every little light has a story to tell.