Toward the rear of the ship. An outer ring shows the equator, poles, tropics, zodiacs, etc.
Inner rings depict the sun, moon, and stars.
The middle of the ship, either lengthwise or widthwise, or both. An astronomical instrument used by ancient Greeks and others to measure the height above the horizon of celestial bodies. The Seaman's astrolabe was a simple device used for measuring the altitude of the sun or a star for fixing one's approximate latitude. It consists of a heavy brass ring fitted with an alidade or sighting rule pivoted at the center of the ring. Suspended vertically from a shackle at the top of the ring, the alidade was positioned to sight the sun or star and the angle was read off on-scale marks on the ring.