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Within these tables, January 1 is always the first day of the year. The Gregorian calendar did not exist before October 15, 1582. Gregorian dates before that are proleptic, that is, using the Gregorian rules to reckon backward from October 15, 1582. Years are given in astronomical year numbering.
There is a disagreement between astronomers and historians about how to count the years preceding year 1. In [Astronomical Algorithms], the 'B.C.' years are counted astronomically. Thus, the year before the year +1 is the year zero, and the year preceding the latter is the year −1. The year which historians call 585 B.C. is actually the year ...
In astronomy and celestial navigation, an ephemeris (/ ɪ ˈ f ɛ m ər ɪ s /; pl. ephemerides / ˌ ɛ f ə ˈ m ɛr ɪ ˌ d iː z /; from Latin ephemeris 'diary', from Ancient Greek ἐφημερίς (ephēmerís) 'diary, journal') [1] [2] [3] is a book with tables that gives the trajectory of naturally occurring astronomical objects and artificial satellites in the sky, i.e., the position ...
The Julian period is a chronological interval of 7980 years, derived from three multi-year cycles: the Indiction, Solar, and Lunar cycles. The last year that was simultaneously the beginning of all three cycles was 4713 BC (−4712), [2] so that is year 1 of the current Julian period, making AD 2025 year 6738 of that Period. The next Julian ...
However, the mean tropical year is not suitable as a unit of measurement because it varies from year to year by a small amount, 6.14 × 10 −8 days according to Newcomb. [5] In contrast, the Julian year is defined in terms of the SI unit one second , so is as accurate as that unit and is constant.
The mean tropical year in 2000 was 365.24219 ephemeris days, each ephemeris day lasting 86,400 SI seconds. [3] This is 365.24217 mean solar days . [ 4 ] For this reason, the calendar year is an approximation of the solar year: the Gregorian calendar (with its rules for catch-up leap days ) is designed so as to resynchronise the calendar year ...
The algorithm enables a computer to print calendar and diary pages for past or future sequences of any desired length from the reform of the calendar, which in England was 3/14 September 1752. The article Date of Easter gives algorithms for calculating the date of Easter. Combining the two enables the page headers to show any fixed or movable ...
A year has about 365.24 solar days but 366.24 sidereal days. Therefore, there is one fewer solar day per year than there are sidereal days, similar to an observation of the coin rotation paradox. [5] This makes a sidereal day approximately 365.24 / 366.24 times the length of the 24-hour solar day.