Annie Jump Cannon

What if I told you one person sorted hundreds of thousands of stars by their color? Her name was Annie Jump Cannon. She lived from 1863 to 1941 and worked in the late 1800s and early 1900s. She became a famous astronomer who solved a big problem: how to organize the stars.

Annie worked at the Harvard College Observatory as one of the team known as the 'Harvard Computers.' Her single most important contribution was making a simple, powerful system to sort stars by the light they give off — their spectra. This made studying the sky much easier.

She looked at photographs of starlight called spectra and watched for tiny dark and bright lines — like fingerprints for stars. Annie arranged the classes into the familiar order O, B, A, F, G, K, M (hot blue stars to cool red ones). Over her career she classified about 350,000 stars.

Why does this matter? Her clear ordering helped scientists learn how hot stars are, how they change with time, and how to compare stars across the sky. Because of her work, astronomers could turn messy lists into a useful map and discover more about how stars live and die.

Annie Jump Cannon turned a sky of sparkling dots into a map scientists could read. She worked carefully even though she was partly deaf, and she became one of history's most important women in science. Next time you look up, remember she helped the stars tell us their colors and temperatures.