“Annie Jump Cannon & Henrietta Swan Leavitt, 1913” by unattributed – Harvard University Library. Licensed under Public Domain via Wikimedia Commons – http://commons.wikimedia.org/wiki/File:Annie_Jump_Cannon_%26_Henrietta_Swan_Leavitt,_1913.jpg#/media/File:Annie_Jump_Cannon_%26_Henrietta_Swan_Leavitt,_1913.jpg