ERA00 Function

  1. astro_module.f90
  2. astro_module
  3. ERA00

public function ERA00(dj1, dj2) result(era)

Earth rotation angle (IAU 2000 model).

Status: canonical model.

Notes

  1. The UT1 date DJ1+DJ2 is a Julian Date, apportioned in any convenient way between the arguments DJ1 and DJ2. For example, JD(UT1)=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)

    The JD method is the most natural and convenient to use in cases where the loss of several decimal digits of resolution is acceptable. The J2000 and MJD methods are good compromises between resolution and convenience. The date & time method is best matched to the algorithm used: maximum accuracy (or, at least, minimum noise) is delivered when the DJ1 argument is for 0hrs UT1 on the day in question and the DJ2 argument lies in the range 0 to 1, or vice versa.

  2. The algorithm is adapted from Expression 22 of Capitaine et al.

    1. The time argument has been expressed in days directly, and, to retain precision, integer contributions have been eliminated. The same formulation is given in IERS Conventions (2003), Chap. 5, Eq. 14.

References

  • Capitaine N., Guinot B. and McCarthy D.D, 2000, Astron. Astrophys., 355, 398-405.

  • McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003), IERS Technical Note No. 32, BKG (2004)

History

  • IAU SOFA revision: 2009 December 15

Arguments

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

UT1 as a 2-part Julian Date (see note)
real(kind=wp), intent(in) :: dj2

UT1 as a 2-part Julian Date (see note)

Return Value real(kind=wp)

the Earth rotation angle (radians), in the range 0 to 2pi.


Calls

proc~~era00~~CallsGraph proc~era00 ERA00 proc~anp ANP proc~era00->proc~anp

Called by

proc~~era00~~CalledByGraph proc~era00 ERA00 proc~apco13 APCO13 proc~apco13->proc~era00 proc~c2t00a C2T00A proc~c2t00a->proc~era00 proc~c2txy C2TXY proc~c2txy->proc~era00 proc~gmst06 GMST06 proc~gmst06->proc~era00 proc~gst06 GST06 proc~gst06->proc~era00 proc~gmst00 GMST00 proc~gmst00->proc~era00 proc~aper13 APER13 proc~aper13->proc~era00 proc~apio13 APIO13 proc~apio13->proc~era00 proc~c2t00b C2T00B proc~c2t00b->proc~era00 proc~c2t06a C2T06A proc~c2t06a->proc~era00 proc~atco13 ATCO13 proc~atco13->proc~apco13 proc~gst06a GST06A proc~gst06a->proc~gst06 proc~atio13 ATIO13 proc~atio13->proc~apio13 proc~atoi13 ATOI13 proc~atoi13->proc~apio13 proc~ee06a EE06A proc~ee06a->proc~gmst06 proc~ee06a->proc~gst06a proc~gst00a GST00A proc~gst00a->proc~gmst00 proc~atoc13 ATOC13 proc~atoc13->proc~apco13 proc~c2tpe C2TPE proc~c2tpe->proc~gmst00 proc~gst00b GST00B proc~gst00b->proc~gmst00

Contents

Source Code

ERA00

Source Code

    function ERA00 ( dj1, dj2 ) result(era)

    implicit none

    real(wp),intent(in) :: dj1 !! UT1 as a 2-part Julian Date (see note)
    real(wp),intent(in) :: dj2 !! UT1 as a 2-part Julian Date (see note)
    real(wp) :: era !! the Earth rotation angle (radians), in the range 0 to 2pi.

    real(wp) :: d1, d2, t, f

    !  Days since fundamental epoch.
    if ( dj1 < dj2 ) then
       d1 = dj1
       d2 = dj2
    else
       d1 = dj2
       d2 = dj1
    end if
    t = d1 + ( d2-dj00 )

    !  Fractional part of T (days).
    f = mod ( d1, 1.0_wp ) + mod ( d2, 1.0_wp )

    !  Earth rotation angle at this UT1.
    era = ANP ( d2pi * ( f + 0.7790572732640_wp &
                           + 0.00273781191135448_wp * t ) )

    end function ERA00