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CO_NUTATE

CO_NUTATE

## Purpose

Calculate changes in RA and Dec due to nutation of the Earth's rotation

## Explanation

Calculates necessary changes to ra and dec due to
the nutation of the Earth's rotation axis, as described in Meeus, Chap 23.
Uses formulae from Astronomical Almanac, 1984, and does the calculations
in equatorial rectangular coordinates to avoid singularities at the
celestial poles.

## Calling Sequence

CO_NUTATE, jd, ra, dec, d_ra, d_dec, [EPS=, D_PSI =, D_EPS = ]

## Inputs

JD: Julian Date [scalar or vector]
RA, DEC : Arrays (or scalars) of the ra and dec's of interest
Note: if jd is a vector, ra and dec MUST be vectors of the same length.

## Outputs

d_ra, d_dec: the corrections to ra and dec due to nutation (must then
be added to ra and dec to get corrected values).

## Optional Output Keywords

EPS: set this to a named variable that will contain the obliquity of the
ecliptic.
D_PSI: set this to a named variable that will contain the nutation in the
longitude of the ecliptic
D_EPS: set this to a named variable that will contain the nutation in the
obliquity of the ecliptic

## Example

(1) Example 23a in Meeus: On 2028 Nov 13.19 TD the mean position of Theta
Persei is 2h 46m 11.331s 49d 20' 54.54". Determine the shift in
position due to the Earth's nutation.

IDL> jd = JULDAY(11,13,2028,.19*24) ;Get Julian date
IDL> CO_NUTATE, jd,ten(2,46,11.331)*15.,ten(49,20,54.54),d_ra,d_dec
====> d_ra = 15.843" d_dec = 6.217"

NUTATE

## Revision History

Written Chris O'Dell, 2002
Vector call to NUTATE W. Landsman June 2002

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