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NUTATE

NUTATE

Name


      NUTATE

Purpose


      Return the nutation in longitude and obliquity for a given Julian date

Calling Sequence


      NUTATE, jd, Nut_long, Nut_obliq

Input


      jd - Julian ephemeris date, scalar or vector, double precision

Output


      Nut_long - the nutation in longitude, same # of elements as jd
      Nut_obliq - nutation in latitude, same # of elements as jd

Example


      (1) Find the nutation in longitude and obliquity 1987 on Apr 10 at Oh.
              This is example 22.a from Meeus
        IDL> jdcnv,1987,4,10,0,jul
        IDL> nutate, jul, nut_long, nut_obliq
            ==> nut_long = -3.788 nut_obliq = 9.443
           
      (2) Plot the large-scale variation of the nutation in longitude
              during the 20th century
      IDL> yr = 1900 + indgen(100) ;Compute once a year
      IDL> jdcnv,yr,1,1,0,jul ;Find Julian date of first day of year
      IDL> nutate,jul, nut_long ;Nutation in longitude
      IDL> plot, yr, nut_long
      This plot will reveal the dominant (18.6 year) period, but a finer
      grid is needed to display the shorter periods in the nutation.

Method


      Uses the formula in Chapter 22 of ``Astronomical Algorithms'' by Jean
      Meeus (1998, 2nd ed.) which is based on the 1980 IAU Theory of Nutation
      and includes all terms larger than 0.0003".

Procedures Called


      POLY() (from IDL User's Library)
      CIRRANGE, ISARRAY() (from IDL Astronomy Library)

Revision History


      Written, W.Landsman (Goddard/HSTX) June 1996
      Converted to IDL V5.0 W. Landsman September 1997
      Corrected minor typos in values of d_lng W. Landsman December 2000
      Updated typo in cdelt term December 2000
      Avoid overflow for more than 32767 input dates W. Landsman January 2005



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