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CO_ABERRATION

CO_ABERRATION

Name


    CO_ABERRATION

Purpose


    Calculate changes to Ra and Dec due to the effect of annual aberration

Explanation


      as described in Meeus, Chap 23.

Calling Sequence


      co_aberration, jd, ra, dec, d_ra, d_dec, [EPS = ]

Inputs


      jd : Julian Date [scalar or vector]
      ra, dec : Arrays (or scalars) of the ra and dec's in degrees
  Note: if jd is a vector, then ra and dec must either be scalars, or
                vectors of the same length.

Outputs


      d_ra, d_dec: the corrections to ra and dec due to aberration in
                    arcseconds. (These values can be added to the true RA
                    and dec to get the apparent position). Note that d_ra
                    is *not* multiplied by cos(dec), so that
                    apparent_ra = ra + d_ra/3600.

Optional Input Keyword


      eps : set this to the true obliquity of the ecliptic (in radians), or
        it will be set for you if you don't know it (in that case, set it to
                an empty variable).

Example


  Compute the change in RA and Dec of Theta Persei (RA = 2h46m,11.331s, Dec =
  49d20',54.54") due to aberration on 2028 Nov 13.19 TD
      IDL> jdcnv,2028,11,13,.19*24,jd ;Get Julian date
      IDL> co_aberration,jd,ten(2,46,11.331)*15,ten(49,20,54.54),d_ra,d_dec
      ==> d_ra = 30.045" (=2.003s) d_dec = 6.697"

Notes


  These formula are from Meeus, Chapters 23. Accuracy is much better than 1
  arcsecond.
  The maximum deviation due to annual aberration is 20.49" and occurs when the
  Earth velocity is perpendicular to the direction of the star.

Revision History


  Written, June 2002, Chris O'Dell, U. of Wisconsin
  Fix error with vector input W. Landsman June 2009
  June 2009 update fixed case where JD was scalar but RA,Dec were vectors, but
    broke the case when both JD and RA,Dec were vectors Aug 2012 W. Landsman
  Further fix when JD is 1 element vector W. Landsman



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