Pillars of Creation: NASA (public domain)
Probability density of hydrogen electron (s,2): Florian Marquardt/ Wikipedia (Creative Commons license)
Grand Central clock: publicdomainpictures.net (public domain)
jakes4a: osInteractive, LLC
Substantial material, especially on 'Homework' page, from Professors Michael Weissman and (it is presumed) Jon Thaler. 'Term paper info' page features contributions, or likely contributions, from Professors David Ceperley, Anthony Leggett, Weissman, & Thaler.