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At 19:23 18/05/2012, you wrote:

>I have spent some free time updating the Bowditch Long term almanac,
>now with base year 2008.

How did you go about doing that? Did you use the quadrennial
corrections given in Bowditch?


>Any ideas how to verify that it works?
>As for the testing I have tried several random times/dates and have
>not been out more than 2.4' on sun and 1.9' on star (yet).

I checked my LTA using a statistical sample testing procedure. The
errors were typically less than 0.3' over 50 years compared to full
blown theoretical predictions, and never more than 0.7'.

The quadrennial corrections depend on the epoch and the period over
which the LTA is supposed to be valid. I found that linear (single
term) quadrennial corrections are sufficient for a period of about 50
years, but accuracy drops off rapidly (errors greater than 1') if you
try to try to use linear corrections for longer period of validity than that.

One problem with with the LTA given in Bowditch (at least, in my 1981
edition) is that the period of validity is not given. Too, simply
transplanting the quadrennial corrections for a 1972 epoch from
Bowditch and hoping they will work for a 2008 epoch is not a valid procedure.

Anyway, as far as I can tell, the quadrennial corrections given in
Bowditch did not even work very well for a 1972 epoch, which makes me
suspect that somebody took an even older set of quadrennial
corrections and transferred them to 1972!

Geoffrey Kolbe

   

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