Julian Date and JD Number Number For Any Julian or Gregorian Calendar Date
and Time and Optional Delta T
Date:   ±Y  M  D   (Neg/Pos = BC/AD) Time UT:   H M S ΔT:   ± H M S
Calendar Input Mode:    Julian              Gregorian 
J   2017     March
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     March
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  
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GENERAL JD NUMBER AND JULIAN DATE FOR GIVEN CALENDAR MODE, DATE AND TIME
WITH OPTIONAL DELTA T

DATE = 2017 March 27 - Monday (Gregorian)

Time  UT HMS =  00:00:00 =  0.00000000 day
Delta T ±HMS = +00:00:00 = +0.00000000 day

JD12 = 2457840 = JD For 12h (midpoint of date) = Julian Day number for date
JD00 = 2457839.5 = (JD12 - 0.5) = JD for 00h (beginning of date)
JDTT = 2457839.5 = (JD00 + UTFrac + dTFrac) = Full Astronomical JD

TIME VARIABLES CORRESPONDING TO JD AND RECKONED FROM J2000.0
J2000.0 = 2000 Jan 01 at 12h TT
      T = 0.1723340177 Julian centuries reckoned from J2000.0
      t = 0.0172334017 Julian millennia reckoned from J2000.0

DIFFERENCE BETWEEN GREGORIAN AND JULIAN CALENDARS
Gregorian calendar date = Julian calendar date plus 13 days 

Julian calendar date = Gregorian calendar date minus 13 days 

Note that the corresponding days of the week are the same on both calendars
regardless of the actual number of days difference between the calendars.
Jay Tanner - 2017 - v3.4