Name

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      NUTATE

Purpose

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

Calling Sequence

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      NUTATE, jd, Nut_long, Nut_obliq

Input

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

Output

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

Example

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      (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

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      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

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

Revision History

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      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