At Harvard College Observatory (now the Center for Astrophysics | Harvard & Smithsonian), Women Astronomical Computers studied glass plate photographs of the night sky. Here they cataloged stars, identified variables, interpreted stellar spectra, counted galaxies, and measured the vast distances in space. Several of them made game-changing discoveries in astronomy and astrophysics. For Women's History Month, Project PHaEDRA is focusing on the notebooks of Women Astronomical Computers who made observations at the Maria Mitchell Observatory while associated with Harvard. The Maria Mitchell Observatory is located in Nantucket, Massachusetts, and was so named in 1908 after the first well-known American woman astronomer. Two of the Women Astronomical Computers served as the first directors of the Maria Mitchell Observatory after their time at Harvard; Margaret Harwood (1912-1957) and Dorrit Hoffleit (1957-1978). We are interested in the work that the Women Astronomical Computers were doing at the Maria Mitchell Observatory, and how this space may have furthered their careers and allowed them to work alongside and beneath the authority of other women. In this mini collection are notebooks by Margaret Harwood, Linda Lucignani, Dorrit Hoffleit, Francis Woodworth Wright, and others. Recently, research material originally produced during the mid-to-late 19th and early 20th centuries by researchers at the Harvard College Observatory was re-discovered in the HCO Plate Stacks holdings. These early notebooks and other materials are absolutely irreplaceable. The material represents the history of the Harvard College Observatory and comprises remarkable examples of primary source material showing the evolution of observation methods, along with early astronomy as a whole. The documents are also relevant to the history of women in science as the collection contains material produced by the Women Astronomical Computers. Women like Williamina Fleming, Annie Jump Cannon, Henrietta Swan Leavitt, Cecilia Payne-Gaposchkin and Antonia Maury made their mark in astronomy (and history!) here by studying these glass plates and publishing their findings in their own name. See an interesting bit, note, or image in the margins? Tell us about it on Twitter or Instagram @ProjectPHaEDRA ! For more information about this collection, check out the Plate Stacks website or contact the John G. Wolbach Library and ask about Project PHaEDRA. If you're a teacher or student, check out our resources about the Harvard Computers and other female astronomers on the Smithsonian Learning Lab.