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. In these books, you can follow the work of Sylvia and Muriel Mussells, two sisters who worked at the Harvard College Observatory in the 1920s and 1930s. Muriel Mussells discovered three new ring nebulae in the Milky Way and Sylvia Mussells discovered the first dwarf galaxy. You can help us find out what else we can learn about them and their work! PLEASE NOTE: The Project PHaEDRA Instructions for Women Computers Notebooks were heavily revised and republished on August 18, 2023. Please take a moment to familiarize yourself with these instructions.