Meridian altitude

Meridian altitude is a method of astronomical navigation used to calculate ones latitude on earth, in this case the latitude of a ship at sea. Using a nautical almanac to determine an estimated time of the meridian altitude of a planet or star, a ship’s captain would then use a sextant to track the  object’s altitude for a few minutes before and during its pass through the meridian (in the case of the sun this was usually at noon).