The Julian day number was devised in 1583 by Joseph Scaliger. It is a count of the number of days from noon on January 1, 4713 BCE (-4712) in the Julian proleptic calendar. (This is equivalent to November 24, 4714 BCE in the proleptic Gregorian calendar.) It covers a period of 7980 years because 7980 is the least common multiple of the lengths of three periods used in the Julian calendar: the indiction cycle of 15 years (an ancient system of dating documents), the Metonic cycle of 19 years (related to the lengths of the solar year and the lunar month), and the 28 year solar cycle (which takes account of the four year rule for leap years in the Julian calendar and the seven-day week to produce a 28 year cycle).

The JulianDayNumber( year, month, day ) command returns the modified Julian day number of the date specified by year, month and day.

The value of year must be greater than or equal to $\mathrm{-4800}$, the month value month must be in the range 1..12, and day must equal a valid day of the month month.

The modified Julian day number of a date is equal to the Julian day number offset by the value $\mathrm{-2.4000005}\times {10}^6$. This results in smaller numerical values, and represents a day count from midnight, rather than noon.

The ModifiedJulianDayNumber( y, m, d ) command returns the modified Julian day number of the date specified by year, month and day.

$\mathrm{with}\left(\mathrm{Calendar}\right)\:$

$\mathrm{JulianDayNumber}\left(2017\,11\,3\right)$

$2458061$

$\mathrm{ModifiedJulianDayNumber}\left(2017\,11\,3\right)$

$58060.5$

$\mathrm{JulianDayNumber}\left(-4713\,11\,24\right)$

$0$

$\mathrm{JulianDayNumber}\left(1940\,2\,30\right)$

Error, (in Calendar:-JulianDayNumber) day number 30 is greater than the number 29 of days in the 2nd month

The Calendar[JulianDayNumber] and Calendar[ModifiedJulianDayNumber] commands were introduced in Maple 2018.

For more information on Maple 2018 changes, see Updates in Maple 2018.