[AZ-Observing] Re: Rigorous Precession

  • From: Stan Gorodenski <stanlep@xxxxxxxxxxxxx>
  • To: az-observing@xxxxxxxxxxxxx
  • Date: Sat, 22 May 2010 12:11:42 -0700

I did not know you had worked with Dick and Helen Lines years ago. I 
used to visit them and their location in Mayer is one reason I bought 
and put up  my observatory where I did. Unfortunately, Dick passed away 
in 1991, and the property was sold (to an amateur).

I am sure the book you are suggesting is very good, but also, the 
formulas in "The Sky Catalogue 2000.0" are very adequate for what AJ is 
doing, I believe. They gave almost exact estimates of RA and DEC for 
Polaris that Bradley measured in 1755, RA 0h 43m 42.2s vs. 0h 43m 43s, 
Dec 87degrees 59' 41'' vs. 87degrees 59' 41''. Since this is so accurate 
going back 245 years, it seems safe to assume they would be very 
accurate for smaller time periods. The "The Sky Catalogue 2000.0" has 
the proper motions for all (as far as I can see) the stars down to 8th 
magnitude. If anyone is interested in the algorithms from this book, I 
can scan the two pages and put them on my web space.

Of course, you are more an expert than me and so your judgment reigns.

On 5/22/2010 11:02 AM, Ken Sikes wrote:
> AJ, I am familiar with the program you are talking about, Bill Anderson and
> I once talked about the 1875 version. At that time the constellation
> boundaries followed simpler lines. Over time the boundary lines have changed
> and that program is not as accurate. There is a newer program, but it is
> difficult to use.
> When you say "objects" are you referring to DSO's or stars? If stars one has
> to take into account the proper motion of the star as well when calculating
> the new location and constellation. Bill and I had a very long and deep
> conversation about this one time at Hovatter and he concluded that the new
> program would be more work that gain.
> If one was going to precess coordinates to a specific date say Aug 20, 2010
> then the primary constants would remain the same and the only change would
> be the spherical coordinates. The book I mentioned to Stan is excellent for
> this and you are welcome to borrow it if you like.
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