The Calendar, the Day and the Hour

Periodic signals for outer space were first systematically used for measurement of time. The task of creating calendars, counting days, and measuring hours was facilitated by observing the periodic motion of bodies in the sky, principally the Sun and the Moon. Different types of calendars, SolarCalendarsolar, lunarCalendarlunar and lunisolarCalendarlunisolar, were invented by different societies. Each calendar has its specific characteristics. Efforts were continuously made to improve the calendar as well as the divisions of time. EclipsesEclipse, though not useful for calendrical purposes, also provided another rhythm, one with much longer periodicity. Study of ancient eclipses helps us to synchronise ancient and modern calendars. The prime division of the day, the hour, initially followed the movement of the Sun. Periodic motionMotion, periodic of the bodies in the solar system was used to find out the longitudeLongitude both on land and on sea.