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NUTATE

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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