The optical device which the astronauts used for navigation while in the Apollo Lunar Module (LM) is an alignment optical telescope (AOT). The AOT was a periscope-type device that protruded through the top of the LM. The astronauts used AOT to make direct visual sightings and record precise angular measurements of pairs of celestial objects. This information was transferred to the Module's guidance computer, which determined the spacecraft's attitude and permitted the alignment of its intertial guidence system.
This item is an unflown surplus production version with the manufacturer's serial number 6. NASA transferred it to the Smithsonian in 1975.