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Gary, you wrote:
"It looks like you are making it too hard. I always come back to to the 
question, "how accurate do you need your position to be?" "

If we can tolerate thirty mile errors, then hey, just use a kamal, etc. :-) 
But that isn't the point here, right? What kind of errors can one expect from 
using a 2006 almanac in 2010? It's a rather specific question.

And you wrote:
"If you can tolerate an error of up to one NM then you can use one set of 
star positions for at least one year on both sides of the date of the 
star positions."

That's good data, but not relevant to this question. He asked about using a 
2006 almanac in 2010. That's not one year.

You concluded:
"So using the December 31, 2009 star positions for all of 2010 will not 
result in "errors of a few minutes of arc"  that you are worried about."

But, Gary... You know that he didn't ask about 12-31-2009. He asked about a 
2006 almanac, which is a very reasonable thing to ask considering the leap 
year cycle for solar position data. As for the stars, if you use a 2006 
Nautical Almanac in 2010, you need to correct for precession (primarily 
precession, with other smaller effects). And to correct for precession, the 
simple correction for GHA Aries which you gave is insufficient, though it 
might be a good place to begin.

Let's try two specific cases: Capella and Kochab. What are their positions in 
the Nautical Almanac in 2006? What would they be in 2010?

-FER


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