idlastro / Astronomical Utilities: NUTATE

[Source code]

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