All of these images are in the public domain courtesy of NASA. blue-marble-west.jpg: http://visibleearth.nasa.gov/view_rec.php?id=2429 cloud.jpg: www.spacetelescope.org/images/html/heic0601a.html comet.jpg: http://hubblesite.org/newscenter/newsdesk/archive/releases/2004/52/ earth-horizon.jpg: http://spaceflight.nasa.gov/gallery/images/station/crew-7/html/iss007e16249.html galaxy-ngc3370.jpg: http://hubblesite.org/newscenter/newsdesk/archive/releases/2003/24/ helix-nebula.jpg: http://hubblesite.org/newscenter/newsdesk/archive/releases/2003/11/ jupiter.jpg: http://hubblesite.org/newscenter/newsdesk/archive/releases/1999/29/ sombrereo.jpg: http://hubblesite.org/newscenter/newsdesk/archive/releases/2003/28/ whirlpool.jpg: http://hubblesite.org/newscenter/newsdesk/archive/releases/2005/12/image/a