... CFHT Star Trails . ... Henrietta Leavitt Calibrates the Stars . ... Humanity's understanding of the relative brightness and variability of stars was revolutionized by the work of Henrietta Swan Leavitt (1868-1921). Working at Harvard College Observatory, Leavitt precisely calibrated the photographic magnitudes of 47 stars to which all other stars could be compared. ... The bright stars above are well known as heart of the Trapezium, an open cluster of stars in the center of the Orion Nebula. ...