On 20 July 1969, the lunar module Eagle landed in the Sea of Tranquillity, a dark, flat plain of old lava near the Moon’s equator. Neil Armstrong and Buzz Aldrin spent about two and a half hours walking outside, collecting 21.5 kg of rocks and setting up experiments, while Michael Collins circled overhead in the command module Columbia. The plain had been chosen because it was smooth and lit by a low morning Sun, but Armstrong had to steer past a field of boulders by hand and landed with less than a minute of fuel to spare. One of their instruments, a mirror for laser beams sent from the Earth, still works today.
