[AZ-Observing] Re: Polaris Transit

  • From: Stan Gorodenski <stan_gorodenski@xxxxxxxxxxxxx>
  • To: az-observing@xxxxxxxxxxxxx
  • Date: Sun, 04 Mar 2007 11:26:05 -0700

Brian Skiff wrote:

>     For the apparent coords of the Sun, you'd really want to take
>into account one's topocentric position, rather than a straight
>geocentric position (if real precision actually matters), and it could
>be that the RASC Handbook positions are geocentric, or maybe for
>some 'center of Canada' location.  I'd be willing to bet that Bill Gray
>does indeed at least allow for this, but perhaps tweaking of input
>parameters would be involved.  This would account for the tens of
>time-seconds difference Stan quotes, and which ought to be calculable
>to an arc-second or so for any instant (tens of time-sec is a huge 
>error by comparison, so something is amiss).
It probably is the case that the geocentric differences account for the 
tens of time-sec differences. When I verified that Guide had the same 
apparent RA as the Astronomical Almanac, I only changed the longitude to 
that of Greenwich, but kept the latitude the same the same as at my 
location. Maybe this accounts for the time-sec difference, although I do 
not now remember if it was actually as high as tens of time-secs. Tens 
of time secs was close enough for what I am doing and so I wasn't 
concerned about the discrepancy.

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