The woman who discovered how to measure the universe

Mark Mortimer reviews Miss Leavitt’s Stars by George Johnson, in Universe Today:

LeavittMiss Henrietta Swan Leavitt obtained work at Harvard Observatory to review photographic plates. These were coming in fast and furious from the many large observatories being built in the Americas. These plates recorded the moment, but humans needed to interpret the dots. Small differences may be due to atmospheric effects, telescope adjustments, emulsion reactions or human intervention. Yet interpreting dots was considered an unworthy task for men, so women like Miss Leavitt were paid about minimum wage to spend hours every day looking at these plates, comparing each against another and against various metrics. With their effort, characteristics were catalogued for tens of thousands of stars.

…Johnson smoothly takes the reader on a journey through parallax measurements, red-blue shifting, luminosity, galaxies and variables. Certainly there’s Leavitt’s discovery published in 1908 where she noted that brighter variables have longer periods. This observation came in a publication that gave a full account of 1777 variables in the Magellanic Cloud, and was so entitled. We also read of Shapely’s and Curtis’s debate in 1920 on whether the Milky Way was the universe or whether the Milky Way was just one typical galaxy amongst others. Eventually Edwin Hubble used Leavitt’s relationship of Cepheid variables to show that Barnard’s Galaxy was over 700,000 light years away and certainly outside the realm of the Milky Way.

More here.