Henrietta Leavitt Calibrates the Stars . ... Credit Copyright: AAVSO Explanation: Humanity's understanding of the relative brightness and variability of stars was revolutionized by the work of Henrietta Swan Leavitt (1868-1921). ... Leavitt discovered and cataloged over 1500 variable stars in the nearby Magellanic Clouds . From this catalog, Leavitt discovered that brighter Cepheid variable stars take longer to vary, a fact used today to calibrate the distance scale of our universe . ...