Lunar caustic (Med. Chem.), silver nitrate prepared to be used as a cautery; -- so named because silver was called luna by the ancient alchemists. -- Lunar cycle. Same as Metonic cycle. See under Cycle. -- Lunar distance, the angular distance of the moon from the sun, a star, or a planet, employed for determining longitude by the lunar method. - - Lunar method, the method of finding a ship's longitude by comparing the local time of taking (by means of a sextant or circle) a given lunar distance, with the Greenwich time corresponding to the same distance as ascertained from a nautical almanac, the difference of these times being the longitude. -- Lunar month. See Month. -- Lunar observation, an observation of a lunar distance by means of a sextant or circle, with the altitudes of the bodies, and the time, for the purpose of computing the longitude. -- Lunar tables. (a) (Astron.) Tables of the moon's motions, arranged for computing the moon's true place at any time past or future. (b) (Navigation) Tables for correcting an observed lunar distance on account of refraction and parallax. -- Lunar year, the period of twelve lunar months, or 354 days, 8 hours, 48 minutes, and 34.38 seconds.