It's a somber day for spaceflight, as NASA astronaut Alan Bean has died at the age of 86 after falling ill during a trip. He was the fourth person to walk on the Moon, flying aboard Apollo 12, and proved crucial to humanity's understanding of its closest celestial neighbor. He was the only geologist to have walked on the Moon and provided an immensely valuable collection of samples that inform lunar geology to this day. He also led the second of three Skylab crews, staying a then record-setting 59 days as he survayed both the Earth's resources and the Sun.