Henrietta Swan Leavitt (7/4/1868 – 12/12/1921) 1 2 5 6 8 9 10 3 4 7 11 1) Henrietta Leavitt working at HCO, circa 1900. Measuring Variable Stars 2) Plate a2969. Leavitt studied changes in variable stars by inspecting photos of the same section of sky taken on different dates. Photos were imaged through tele­ scopes onto glass plate negatives coated in light-sensitive chemicals. (The bright­ er a star, the more photons reached the plate and the larger its dark dot.) She labeled each star, measuring diameters through a loupe (magnifying glass). 3) Leavitt kept her analyses in handwrit­ ten notebooks. For each plate, she would draw a detailed chart of the stars she was exam- ining as they appeared in the sky. (Mirror image to her markings on the back of the plate. See circled “u” and “v”.) 4) List of magnitudes for each labeled star on plate a2969. Stars were sometimes recalibrated. See 8. Comparing Plates 5) Detail from Plate b20650, exposed for 4 hours on October 20, 1897. Henrietta Swan Leavitt, a deaf American astronomer and graduate of Radcliffe College, worked at the Harvard College Observatory (HCO) as a “computer”, examining glass photographic plates in order to measure and catalog the bright- ness of stars. This work led her to discover the relation between the luminosity and the period of Cepheid variables. Though she received little recognition in her lifetime, Leavitt’s discovery later provided astronomers with the first “stand- ard candle” with which to measure the distance to faraway galaxies. 1 2 Williamina Fleming (5/15/1857 – 5/21/1911) c e a d f 4 5 6 8 9 7 new variable 10 11a 11b 1) Portrait, circa 1890s. Fleming orga­ nized the Draper Catalogue, classifying 10,498 stars, based on 28,266 spectra on 633 plates. By 1910, she had examined ~200,000 HCO photographic plates. 2) Orion Nebula in Glass Plate b10250 (de­ tail), September 8, 1893 with markings by Fleming. 3) b10250 (detail), in which Fleming dis­ covered the Horsehead Nebula. Fleming discovered 10 novae, 59 gaseous nebulae, ~ 300 variable stars, and was the first to recog­ nize the existence of white dwarfs. 4) Photo of Horsehead Nebula; Ken Craw­ ford, Rancho Del Sol Observatory. Note nebula color and position are reversed from negative in 3). Work With Variable Stars 5) Fleming’s notes. She would draw a chart with the new variable, as well as stars near it (red box), then document positions & known magni­ tudes (green). 6) Determining magnitude of new star (Plate i10491) using the “Pickering-Fleming Method” (cyan box): Compare variable star “v” with a known, slightly dimmer star. Note how many Williamina Patton Fleming was the most famous woman astronomer in America during her lifetime. She helped develop a common designation system for stars and showed that variable stars and novae could be identified by their spectra, discovering many. A founding member of the Harvard Computers, a group of female astronomers and analysts at Har­ vard College Observatory (HCO), she supervised other women astronomers and managed publications issued during her time there. A charter member of the Astronomical and Astrophysical Society, she advocated for women in astronomy. Read more about Williamina Fleming at https://library.cfa.harvard.edu/phaedra/fleming 3 The Project PHaEDRA Collection: An Anchor to Connect Modern Science With Historical Data Poster by: Peggy Wargelin, Project PHaEDRA, Wolbach Library, Center for Astrophysics | Harvard & Smithsonian Presented by: Edward Los, Harvard College Observatory, AAVSO Member ABSTRACT Project PHaEDRA (Preserving Harvard's Early Data and Research in Astronomy) is an initiative by the Wolbach Library, in collaboration with many partners, to catalog, digitize, transcribe, and enrich the metadata of over 2500 logbooks and notebooks produced by the Harvard Computers and early Harvard astronomers. Our goal is to ensure that this remarkable set of items, created by a remarkable group of people, is as accessible and useful as possi­ bl