A nautical almanac is a publication describing the positions of a selection of celestial bodies for the purpose of enabling navigators to use celestial navigation to determine the position of their ship while at sea. The Almanac specifies for each whole hour of the year the position on the Earth's surface at which the Sun, Moon, planets, and First Point of Aries is directly overhead. The positions of 57 selected stars are specified relative to the First Point of Aries.