Lunar distance (navigation)

In celestial navigation, lunar distance is the angle between the Moon and another celestial body. The lunar distances method uses this angle, also called a lunar, and a nautical almanac to calculate Greenwich time. By comparing that calculated time to the measured local time, the navigator can determine longitude. The method was used for some time during the 18th century, before the introduction of the marine chronometer. A similar method uses the positions of the Galilean moons of Jupiter.