NavList:

John,

You wrote:

Like a lot of equations in navigation it is either + or - depending on whether the Latitude and Declination are the same or different. In this case they are different and so the appropriate sign is +.

I just tried an example and I'm not so sure about this. Here are my calculations:

2015 Jan. 21  06:30:00 UT

My actual position: 37°03.3' N, 76°28.6' W

Rigel Ho: 16°11.2'  GHA: 138°59.3'  Dec. S8°11.4'

First, I used "-":

cos-1((sin(16°11.2') - sin(-8°11.4') · sin(37°3.3')) / (cos(-8°11.4') · cos(37°3.3'))) = 62°30.7' = LHA

138°59.3' - 62°30.7' = 76°28.6' W = my actual longitude

Then, I used "+":

cos-1((sin(16°11.2') + sin(-8°11.4') · sin(37°3.3')) / (cos(-8°11.4') · cos(37°3.3'))) = 75°51.8' = LHA

138°59.3' - 75°51.8' = 63°07.5' W ≠ my actual longitude

I got similar results when working another example using south latitude and north declination. Am I doing something wrong?

Regards,

Sean C.