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The Julian date (JD) of any instant is the Julian day number plus the fraction of a day since the preceding noon in Universal Time. Julian dates are expressed as a Julian day number with a decimal fraction added. [8] For example, the Julian Date for 00:30:00.0 UT January 1, 2013, is 2 456 293.520 833. [9]
Terrestrial Time (TT) is a modern astronomical time standard defined by the International Astronomical Union, ... is the TCG time expressed as a Julian date ...
The Julian day number is a simplified time-keeping system originally intended to ease calculation with historical dates which involve a diversity of local, idiosyncratic calendars. It was adopted by astronomers in the mid-1800s, and identifies each date as the integer number of days that have elapsed since a reference date ( "epoch" ), chosen ...
The Julian calendar has two types of year: "normal" years of 365 days and "leap" years of 366 days. There is a simple cycle of three "normal" years followed by a leap year and this pattern repeats forever without exception. The Julian year is, therefore, on average 365.25 days long.
A commonly used value in Lilius's time, from the Alfonsine tables, is 365.2425463 days. [13] As the average length of a Julian year is 365.25 days, the Julian year is almost 11 minutes longer than the mean tropical year. The discrepancy results in a drift of about three days every 400 years.
Universal Time (UT or UT1) is a time standard based on Earth's rotation. [1] ... where T u = (Julian UT1 date − 2451545.0). [2] History.
Except where stated otherwise, the transition was a move by the civil authorities from the Julian to the Gregorian calendar. In religious sources it could be that the Julian calendar was used for a longer period of time, in particular by Protestant and Eastern Orthodox churches. The historic area does not necessarily match the present-day area ...
The tables below list equivalent dates in the Julian and Gregorian calendars. Years are given in astronomical year numbering . This is a visual example of the official date change from the Julian calendar to the Gregorian