Henrietta Swan Leavitt was born on July 4, 1868 in Lancaster, Massachusetts.

Henrietta Leavitt isn't a well known name, but a century ago she made one of the most important discoveries of 20th century astronomy. Previously, astronomers could only measure distances up to 100 light years, but her work extended that to 10 million light years.

She discovered the relationship that makes it possible to use Cepheid variable stars to calculate cosmic distances. It was traditionally known as the period-luminosity relation. This name completely bypassed its discoverer. It wasn't until 2009 that the American Astronomical Society agreed to encourage people to refer to it as the “Leavitt Law”. This usage has since become more common.

Although she made a revolutionary discovery, her life left almost no footprints on history. The book Miss Leavitt's Stars contrasts the solidity of her professional accomplishment with the butterfly touch of her life. Miss Leavitt isn't even the star of her own biography.

Mona Evans
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