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Posted on @rawstates
The Harvard College Observatory and its 600,000 glass plates
Cambridge, Massachusetts
Public domain · Wikimedia Commons
From the 1880s the observatory photographed the sky onto glass and hired women at low wages to measure the plates. Working from that pile, Henrietta Swan Leavitt found the relationship between a Cepheid variable's period and its brightness, which is how anyone can measure the distance to another galaxy. Annie Jump Cannon built the stellar classification scheme still in use. The plate stacks hold about 600,000 plates covering a century of sky.
That was 1 of the hidden places.
Location: historic site
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