ALT A Mark Twain graphic with a quote and a photograph of Twain in Tesla's lab.

ALT Photograph of Earth captured by the Apollo 17 crew on December 7, 1972. Earth takes up most of the image. Dark blue ocean water and swirling white clouds are visible. Africa is a large brown landmass from the center to the upper left, stretching from about 9 to 12 o'clock. Clouds cover most of the 6 o'clock. Credit: NASA

ALT A full disk image of Earth, as seen from the Orion capsule. The planet is a pale blue, swirling with white clouds and glowing slightly lighter blue in place from reflected light. From about 8 to 9 o'clock, a large brown landmass is Africa, with the Iberian peninsula twinkling with lights just where the planet curves. At the 1 o'clock spot, aurora glow in a thin green glow, just barely separated from the planet's surface. Earth is set against the black of space. Credit: NASA/Reid Wiseman