Inverse JD (Julian Date) Calculator For the Julian and Gregorian Calendars

Enter any positive JD Number or Julian Date in the range from
JD = 0.0   to   JD = 5373484.5    to compute the corresponding
dates and times on the Julian and Gregorian calendars




Calendar Input Mode:    Julian              Gregorian 
J   2017     October
SunMonTueWedThuFriSat
            1
2 3 4 5 6 7 8
9 10 11 12 13 14 15
16 17 18 19 20 21 22
23 24 25 26 27 28 29
30 31          
      
G   2017     October
SunMonTueWedThuFriSat
1 2 3 4 5 6 7
8 9 10 11 12 13 14
15 16 17 18 19 20 21
22 23 24 25 26 27 28
29 30 31        
For JD (Julian Date) 2458045 on the Gregorian Calendar, the
corresponding JD number, calendar date and time is:

JD (Julian Date)JD NumberGregorian Calendar DateTime
245804524580452017 October 18 Wed12:00:00.000

NOTE:
There is a distinction to be made between the JD (Julian Date) and the JD (Julian Day) Number. They are not always numerically equivalent but can sometimes be confused as such because they can sometimes be equivalent.

The JD (Julian Date) corresponds to a specific date and time of day. It is usually a fractional value and only equates to an integer value at noon on the corresponding date, at which point it also equates to the standard JD Number for that calendar date. This is the only time that the Julian Date and the JD number happen to be numerically equivalent.

The JD (Julian Day) Number is ALWAYS an integer value. It is simply the sequential serial count of the number of calendar days since the mathematical origin of the respective calendar system to which it applies.

Every date on either the Julian or Gregorian calendar system has a unique sequential date serial number called the Julian Day Number, always a positive integer, usually simply called the JD number, to distinguish it from all other dates on the calendar. The only thing the JD number tells us is the date on the calendar. When the time of day is involved, then we use the general Julian Date, usually abbreviated to JD, with the fractional part of it referring to the time of day on the given date.
Calendar   Mathematical Origin        (JD = 0.0,  JD Num = 0)
---------  --------------------------------------------------
Julian     -4712 Jan 01.5  =  4713 BC Jan 01 Mon 12:00:00.000
Gregorian  -4713 Nov 24.5  =  4714 BC Nov 24 Mon 12:00:00.000
Given any general JD (Julian Date) value, the corresponding JD Number value and day of the week (DoW) index are found by:
JDNum = floor(JD + 0.5)

DoW = (JDNum + 1) mod 7

The DoW indices are:  0=Sun, 1=Mon, ..., 6=Sat
The DoW index formula applies equally to both the Julian and Gregorian calendars.

Jay Tanner - 2017