NUTATE

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

       NUTATE, jd, Nut_long, Nut_obliq

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

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

       (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.

       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".

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

       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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