Celebrating the "blue Marble"

An unplanned photograph taken more than 20,000 miles from Earth may have had more influence on humanity than any other photograph in our history. Forty years ago this week, on 7 December 1972, geologist Harrison "Jack" Schmitt, an astronaut and a member of the crew of Apollo 17, took the photograph of the Earth that is often credited with changing the way people think about our planet. The first photograph of the entire round, fully illuminated Earth was snapped at more than 20,000 miles from Earth a little more than 5 hours after Apollo 17's launch. Apollo 17, on its way to the Moon and with the capsule oriented such that the Sun was directly facing the Earth, had reached a distance far enough away for the crew to see the entire planet [Reinert, 2011]. The crew was instructed not to take photographs at that time, but the astronauts were fascinated by their views of the Earth.