Time is defined by the Oxford Dictionary as “the indefinite progress of existence and events in the past, present and future regarded as a whole in an irreversible succession.” Time has different definitions that often depend upon the object or device used for measurement. Periodic events like the sun across the sky or moon phases are examples, as are pendulums and hourglasses of various types. Einstein’s theory of relativity is the primary framework for measuring spacetime and has shown that time there can be distorted and dilated, especially near the event horizons at the edges of black holes or when Congress is in session, and the measurement of spacetime may differ according to the position of the observer. As a general rule for those of us presently occupying the earth, chronometry (the measurement of time) is done by either calendar or by clocks. Calendars measure the passage of time in longer periods like days, weeks, months and years, and clocks are most often used to measure periods of time shorter than 24 hours. The celestial movement of the moon, stars and sun have been used by men for over 6,000 years, and lunar calendars featuring 12 and 13 months became a part of many cultures. The Mayan civilization used a religious and astronomically based calendar of 18 months of 20 days each with 5 extra bonus days, and the Egyptian, Coptic and Ethiopian 12-month calendars also feature these 5 extra days (plus one for leap years) to make their calendar “fit” celestial observations. Time is also socially significant in economics and personal values due to a combination of limited time in each day and in the totality of human lifespans.
The Gregorian calendar has been in use by most of the world since 1582 and replaced the Julian calendar. The Gregorian model used the 365.2425 days in the solar year to approximate the actual 365.2422 days in the solar year and allowed a leap year every 4 years to make up the difference between the two figures. The Gregorian, by so doing, shortened the average calendar year by 0.0075 days to keep the spring and autumnal equinoxes (equinoxi?) from drifting, calendar-wise too far from its actual occurrence in the calendar year. This adjustment was important to the Christian calendar because it allowed the March 21st date of the vernal equinox to remain fairly constant, which was necessary to keep the date of Easter within a given timeframe each year. Just as an aside for math people, every year that is divisible by 4 is a leap year except for years that are exactly divisible by 100. Those years are leap years only if they are exactly divisible by 400. 1700, 1800 and 1900, for example, were not leap years, but the year 2000 was. Most of us don’t live long enough for that to be an important consideration, but there it is.
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