One of the most recognizable elements of the lunar module of the Apollo missions.

The alignment optical telescope, mounted on the navigation base to provide mechanical alignment and a common reference between the telescope and the inertial measurement unit, is a unity-power, periscope-type device with a 6 conical field-of-view. It is operated manually by the astronauts. The telescope has a movable shaft axis (parallel to the LM X-axis) and a line-of-sight approximately 45 degrees from the X-axis in the Y-Z plane.