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John,

I think I understand now. I was getting very confused by the attachment on your last post, so I went through all of the math and I think I know why. First, it seems as though you may have accidentally given the wrong sin and cos values for my actual latitude. In the upper right corner, you list the values as 0.59482 and 0.80386 respectively. These are the correct values for the most southerly latitude in the example (36°30' N). A simple error, but it threw me for a loop. It appears you used the correct numbers in your calculations, though.

Next, I noticed you did not include the 'negative sign' in front of the sin of the star's declination. I surmise you are using tables and want to avoid using negative numbers in your calculations, is this correct? I usually use a calculator, so it's trivial to use negative values. So, using the correct sin and cos values for my latitude and ignoring 'signs', I get the correct answer using '+' this time! :) I haven't tried any other examples yet, but I'm sure this is the answer.

I understand the relationships between GHA, LHA and longitude, COPs and GPs well enough, but thanks for taking the time to explain them anyway. I'm sure many other readers will benefit from it.

Cheers,

Sean C.