Julian dating system
Julian dates (abbreviated JD) are simply a continuous count of days and fractions since noon Universal Time on January 1, 4713 BC (on the Julian calendar).
Almost 2.5 million days have transpired since this date.
The Julian calendar has a leap year every fourth year, while the Gregorian calendar has a leap year every fourth year except century years not exactly divisible by 400.Thus, there is a ten-day gap in calendar dates, but no discontinuity in Julian dates or days of the week: 4 October 1582 (Julian) is a Thursday, which begins at JD 2299159.5; and 15 October 1582 (Gregorian) is a Friday, which begins at JD 2299160.5.The omission of ten days of calendar dates was necessitated by the astronomical error built up by the Julian calendar over its many centuries of use, due to its too-frequent leap years.Enter a valid date or Julian date, and click 'Convert'. Enter dates in the form mm/dd/yy, dd-mmm-yyyy, 'today', ' 1 day' or similar.Astronomers, especially variable star observers, commonly use the chronological system of Julian Days to record their observations.
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The Smithsonian Astrophysical Observatory introduced the 'Modified Julian Date' to record the orbit of the Sputnik satellite in 18 bits.