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Various calendar systems have been in use at different times and places around the world.This application deals with only two: the Gregorian calendar, now used universally for civil purposes, and the Julian calendar, its predecessor in the western world.This application assumes that the changeover from the Julian calendar to the Gregorian calendar occurred in October of 1582, according to the scheme instituted by Pope Gregory XIII.Specifically, for dates on or before 4 October 1582, the Julian calendar is used; for dates on or after 15 October 1582, the Gregorian calendar is used.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.
Instructions: Use this tool to convert between date and Julian (yyddd) date formats.The changeover to the Gregorian calendar system occurred as described above only in Roman Catholic countries.However, adoption of the Gregorian calendar in the rest of the world progressed slowly. Seidelmann eds., (Mill Valley, CA: University Science Books), Chapter 15, pp. The modified Julian date (MJD) is related to the Julian date (JD) by the formula: MJD = JD - 2400000.5 This data service uses one of our new Application Programming Interfaces (APIs). Some societies set up calendars based on the moon, or lunar cycle, and some on the sun, or solar cycle.
Many combined the two, inserting extra months when needed, to prevent the two cycles from getting out of phase, and to ensure seasons would begin the same time each year.
Julian dates are widely used as time variables within astronomical software.