The most widely distributed image in human history was shot on a whim, upside down, by an amateur weatherman hurtling through space. This deep dive unpacks the Blue Marble, the photograph of Earth taken on December 7, 1972 by the crew of Apollo 17 from roughly 29,400 kilometers away. The hosts explain why the December solstice trajectory gave the first fully illuminated view of the south polar ice cap, how a modified 70-millimeter camera with an 80-millimeter lens and a 1/250-second shutter froze a planet showing exactly 50 percent cloud cover, and why the original frame had the South Pole at the top.

From there the conversation covers the debate over who pressed the shutter, with onboard audio pointing to geologist and amateur meteorologist Harrison Schmitt, and the counterculture campaign of Stewart Brand, who in 1966 began mailing 25-cen ...