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). > > Brian, 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. Stan -- See message header for info on list archives or unsubscribing, and please send personal replies to the author, not the list.