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The calendar bases the own unit of measure on quantity of fixed duration, (days, months, years) reported to processings of based calculations on the observation of astronomical phenomena, type solar lunation and cycles. Such calculations have, in the course of the historical ages, endured several modifications and interpretations, dictated from the fact that the astronomical cycles are not exactly formed from an entire number of days. As a result of that, we today find ourselves to consider various measurements of the days, between which:

CALENDAR LUNI-SOLAR (Hebrew, Chinese and other Asia)

In the western calendar it is considered the period of revolution of the Earth around the Sun (tropic year), that it is worth 365,2422 days, for this it is considered solar. Considering 365 entire days it would be had in the time one sliding of the seasons. To that bissextile year has been obviated inserting 1 every day 4 years (bissextile year)

In the lunar calendar it is considered the lunar phases, (lunar synodic month) that they have duration of 29,53 days. This resist to having months (12 year) alternated of 29 and 30 days, and consequently the year has one alternated duration of 354 or 355 days.To the comparison with the western one a refuse from 10 to 12 days is had, but after 30 years, they coincide. Such refuse is consequence of the advance of the New Year's Day Muslim regarding the Gregorian. The account of the years is made to begin the 16-7-672 (year of the Egira).

The luni-solar calendar is also it based on the lunar cycle, for which alternate months of 29 and 30 days, re-united in periods of 19 years (cycle of Metone), that they comprise 12 years of 12 months (common year), and 7 years of 13 months (embolism year). The account of the years is made to begin the 3761 B.C. corresponding to the traditional date of the creation of the world.

Gregorian calendar

Astronomer was introduced from the Pope Gregory Xlll in the 1582, in order to correct the previous intentional Julian calendar from Julius Caesar. In fact the astronomers convened in the 46 a.C. from J. Caesar, considered the year, composed from 365 days and 6 hours, instead of the effectives 365 days 5h 48 ' and 46 ". Such difference in excess of 11 ' and 14 ", involved an increment of 1 every day 128 years. In the 1582 a delay of 10 days was therefore accumulated, for which Gregorio Xlll it established that the successive day to a 4 friday October 1582, became 15 saturdays October, bringing back therefore the date of the spring equinox to 21-3. Beyond to this the Pope astronomer it considered also for the future years, in fact it established the abolition of 3 days every 4 centuries, removing from the number of the bissextile years those secular years whose group of the first two figures was not divisible for four. 1700, 1800, 1900 were not bissextile, it will be 2000, 2400. Also this system however is affection from error regarding the seasons, quantify in 1 every day 3300 years. This system of calendar came immediately adopted from the countries of catholic religion, and later on also from the other nations:
in 1700 in Norway and Denmark
in 1752 in England
in 1918 in Russia
in 1932 in Greece

bissextile year

The bissextile year (366 days) servants exactly to recover the 6 hours approximately, of which the calendar year it differs from that solar one. It was introduced for before the time from the Julian reform, came called therefore why the Roman, not wanting for superstition to modify the month, they thought about to make the added one, even to the end of the year, after the sixth antecedent day the calends of March (23 February) that in such a way it came repeated two times, therefore " bis sextus ".

year zero respect b.C. & a.C.

3760 b.C. for the Hebrew the creation of the man.
622 a.C. for the Muslims, Maometto emigrated from the Mecca to Medina.
551 b.C. for the confucianist Chinese, nacque Confucius.
660 b.C. for the Japanese the king Jimmutenno founded the Japanese empire.
284 a.C. for the copti (Christian of Abyssinia, Egypt and Sudan), advent to the throne of Diocletian.

year definition

SIDEREAL YEAR: exact time that the Earth employs in order to complete an entire one turn of revolution around to the Sun; solar 365 gg 6h 9 ' 13 ".
SOLAR YEAR OR TROPICO: interval that passes between two successive ones spring equinoxes; 365 gg 5h 48 ' 46 ".
YEAR LITURGICAL or ECCLESIASTIC: considered for the ceremonies of church; it begins with the Advent (from the come Latin adventus = of the Getlteman).
JUDICIAL YEAR: 1 January - 31 Decembers.
PLANETARY YEAR: time that employs a planet in order to complete one turn of revolution around the Sun.

unit of time reports from 1 second

medium solar day (d) = 8.64*104
sideral day = 8.616409*104
medium solar minute (min) = 60
sideral minute = 59.83617
medium standard time (h) = 3.6*103
sideral hour = 3.59017*103
sideral second = 0.9972696
shake = 1*10-8

dates of Easter

The Christian Easter is Sunday that follows the 1 plenilune that one verification after the of spring equinox, and is inclusive between March 22 and April 25. Such rule has stayed established from the Council of Nicea (325).

The Passover commemorates the liberation from the slavery from Egypt, and has lasted 8 days beginning from the plenilune of March

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