JD2CAL Subroutine

  1. astro_module.f90
  2. astro_module
  3. JD2CAL

public subroutine JD2CAL(dj1, dj2, iy, im, id, fd, j)

Julian Date to Gregorian year, month, day, and fraction of a day.

Status: support routine.

Notes

  1. The earliest valid date is -68569.5 (-4900 March 1). The largest value accepted is 10^9.

  2. The Julian Date is apportioned in any convenient way between the arguments DJ1 and DJ2. For example, JD=2450123.7 could be expressed in any of these ways, among others:

         DJ1            DJ2

 2450123.7D0        0D0        (JD method)
  2451545D0      -1421.3D0     (J2000 method)
 2400000.5D0     50123.2D0     (MJD method)
 2450123.5D0       0.2D0       (date & time method)

  3. In early eras the conversion is from the "Proleptic Gregorian Calendar"; no account is taken of the date(s) of adoption of the Gregorian Calendar, nor is the AD/BC numbering convention observed.

Reference

  • Explanatory Supplement to the Astronomical Almanac, P. Kenneth Seidelmann (ed), University Science Books (1992), Section 12.92 (p604).

History

  • IAU SOFA revision: 2019 June 20

Arguments

TypeIntentOptionalAttributesName
real(kind=wp), intent(in) :: dj1

Julian Date (Notes 1, 2)
real(kind=wp), intent(in) :: dj2

Julian Date (Notes 1, 2)
integer, intent(out) :: iy

year
integer, intent(out) :: im

month
integer, intent(out) :: id

day
real(kind=wp), intent(out) :: fd

fraction of day
integer, intent(out) :: j
  • 0 = OK
  • -1 = unacceptable date (Note 1)

Called by

proc~~jd2cal~~CalledByGraph proc~jd2cal JD2CAL proc~utcut1 UTCUT1 proc~utcut1->proc~jd2cal proc~utctai UTCTAI proc~utcut1->proc~utctai proc~dtf2d DTF2D proc~dtf2d->proc~jd2cal proc~utctai->proc~jd2cal proc~d2dtf D2DTF proc~d2dtf->proc~jd2cal proc~jdcalf JDCALF proc~jdcalf->proc~jd2cal proc~ut1utc UT1UTC proc~ut1utc->proc~jd2cal proc~apco13 APCO13 proc~apco13->proc~utcut1 proc~apco13->proc~utctai proc~apio13 APIO13 proc~apio13->proc~utcut1 proc~apio13->proc~utctai proc~taiutc TAIUTC proc~taiutc->proc~utctai proc~atco13 ATCO13 proc~atco13->proc~apco13 proc~atoi13 ATOI13 proc~atoi13->proc~apio13 proc~atio13 ATIO13 proc~atio13->proc~apio13 proc~atoc13 ATOC13 proc~atoc13->proc~apco13

Contents

Source Code

JD2CAL

Source Code

    subroutine JD2CAL ( dj1, dj2, iy, im, id, fd, j )

    implicit none

    real(wp),intent(in) :: dj1 !! Julian Date (Notes 1, 2)
    real(wp),intent(in) :: dj2 !! Julian Date (Notes 1, 2)
    integer,intent(out) :: iy !! year
    integer,intent(out) :: im !! month
    integer,intent(out) :: id !! day
    real(wp),intent(out) :: fd !! fraction of day
    integer,intent(out) :: j !! status:
                             !! *  0 = OK
                             !! * -1 = unacceptable date (Note 1)

    !  Minimum and maximum allowed JD
    real(wp),parameter :: djmin = -68569.5_wp
    real(wp),parameter :: djmax = 1.0e9_wp

    integer :: jd, l, n, i, k
    real(wp) :: dj, d1, d2, f1, f2, f, d

    !  Check if date is acceptable.
    dj = dj1 + dj2
    if ( dj<djmin .or. dj>djmax ) then
       j = -1
    else
       j = 0

       !  Copy the date, big then small, and re-align to midnight.
       if ( abs(dj1) >= abs(dj2) ) then
          d1 = dj1
          d2 = dj2
       else
          d1 = dj2
          d2 = dj1
       end if
       d2 = d2 - 0.5_wp

       !  Separate day and fraction.
       f1 = mod(d1,1.0_wp)
       f2 = mod(d2,1.0_wp)
       f = mod(f1+f2,1.0_wp)
       if ( f < 0.0_wp ) f = f+1.0_wp
       d = anint(d1-f1) + anint(d2-f2) + anint(f1+f2-f)
       jd = nint(d) + 1

       !  Express day in Gregorian calendar.
       l = jd + 68569
       n = ( 4*l ) / 146097
       l = l - ( 146097*n + 3 ) / 4
       i = ( 4000 * (l+1) ) / 1461001
       l = l - ( 1461*i ) / 4 + 31
       k = ( 80*l ) / 2447
       id = l - ( 2447*k ) / 80
       l = k / 11
       im = k + 2 - 12*l
       iy = 100 * ( n-49 ) + i + l

       fd = f
    end if

    end subroutine JD2CAL