Henrietta Swan Leavitt

Denied a telescope. Ignored by history. But still, Henrietta Swan Leavitt measured the universe. Her discovery unlocked the true scale of space and changed astronomy forever. 🚀✨ #DeafSTEMChronicle #STEMinASL #Astronomy #WomenInSTEM

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Transcript: Henrietta Swan Leavitt was born on July 4, 1868, in Massachusetts, into a large, supportive family. From a young age, Henrietta showed an interest in learning and was encouraged to pursue her studies. She attended Radcliffe College (which was then called the Society for the Collegiate Instruction of Women), where she took courses in astronomy. During her time at college, Henrietta began to lose her hearing. Despite this challenge, she didn't let her partial deafness slow her down.

She developed a passion for studying the stars and began working as a "computer" at the Harvard College Observatory after graduating. At the time, women weren’t allowed to operate telescopes or lead research projects, so many were hired to analyze data collected by male astronomers. Henrietta joined a team of women examining photographic plates of the night sky. Though the work was tedious and repetitive, Henrietta had a sharp eye for detail and a deep curiosity about the universe.

Henrietta Swan Leavitt made one of the most important discoveries in astronomy through her study of a special type of star called a “Cepheid variable.” These stars don’t shine with constant brightness—instead, they regularly get brighter and dimmer in a repeating cycle. Henrietta noticed something remarkable: the brighter the star, the longer it took to complete a full cycle (from bright to dim and back again). In other words, a Cepheid that takes a long time to complete its cycle is intrinsically brighter than one that cycles more quickly. This consistent relationship between a Cepheid’s luminosity (its true brightness) and its period (the length of its cycle) became known as the Leavitt Law, or the Period-Luminosity Relation.

Why was discovery was so important? Astronomers can’t just take a ruler and measure the distance to stars and galaxies directly from Earth. But thanks to Henrietta’s work, they finally had a reliable tool. If you observe a Cepheid star and measure its period—say it takes 10 days to complete its cycle—you can use the Period-Luminosity Law to determine its true brightness (its luminosity), like knowing a light bulb is rated at 1000 watts. But when you actually observe the star, it may appear much dimmer. And if something that bright looks dim, it must be far away. By comparing its true brightness to how bright it appears, astronomers can plug the values into a formula (based on how light dims with distance) to calculate how far away the star is. It’s like knowing how powerful a light bulb is and figuring out its distance based on how dim it appears.

This method allowed astronomers to measure distances across our galaxy and beyond. Henrietta’s discovery was used by scientists like Edwin Hubble to show that galaxies are moving away from each other, proving that the universe is expanding! Even though Henrietta never got the full recognition she deserved during her life, her work provided the key to unlocking the mysteries of the cosmos, helping us understand the true size and scale of the universe. And she did all of this while being partially deaf, communicating through writing and focusing on the science she loved.