While at Wellesley, she took astronomy courses from one of Pickering's star students, Sarah Frances Whiting.[1] She became the first female assistant to study variable stars at night.[4] She studied the light curve of variable stars which could help suggest the type and causation of variation.[4] Cannon considered merging the classification systems developed by Fleming and Maury rather than inventing a brand new one, and developed the Harvard Classification Scheme, which is the basis of the today's familiar O-B-A-F-G-K-M system. She also categorized the variable stars into tables so they could be identified and compared more easily.[4] These systems connect the color of stars to their temperature.