Space sextant

The logic is that of a marine sextant: bring two objects together in the field of view and read the angle off the limb scale. The difference is that the "horizon" is the sunlit edge of the Earth and the measurement is made through a porthole in gloves. The instrument was part of the emergency kit of lunar ships and stations: with communications lost, the crew had to fix their position and compute a manoeuvre themselves. Never used in anger, it remains a telling example of engineering pessimism — a mandatory quality in crewed hardware. On display is the sextant in its stowage case with a reference star chart.