In academia, Leavitt excelled in mathematics courses at Cambridge.[1] When she began working at the observatory she was tasked with measuring star brightness through photometry.[4] She found hundreds of new variable stars after starting to analyze the Great Nebula in Orion and her work was expanded to study the variables of the entire sky with Annie Jump Cannon and Evelyn Leland.[4] With skills gained in photometry, Leavitt compared stars in different exposures. Studying Cepheid variables, in the Small Magellanic Cloud, she discovered that their apparent brightness was dependent on their period. This discovery led to the use of Cepheid variables as a standard candle for determining cosmic distances.[14] That, in turn, led directly to the modern understanding of the true size of the universe, and Cepheid variables are still an essential rung in the cosmic distance ladder.