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Could someone either explain how the expressions for the sine, cosine
and tangent of Z (as discussed on this thread) are derived or else point
me to a published explanation? I have been trying to equate the three
expressions but the trig I was taught as a 16 year-old is far too rusty
for me to make sense of them. Nor can I find an explanation in any of
the texts I have to hand.


Any guesses as to why each textbook seemingly offers only one way of
calculating Z? Any observer must be well aware of whether each of his
sights is close to his meridian or to his prime vertical. So why are we
not told to find Z from its cosine when the body lies to east or west
and from its sine when it lies north or south? That way, ambiguities
would be avoided and we would be working with trigonometric values which
change swiftly with changing azimuth. (And without the complications of
"ATAN2" calculator buttons or other ways of applying George's tangent
approach.)


Trevor Kenchington



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Trevor J. Kenchington PhD                         Gadus@iStar.ca
Gadus Associates,                                 Office(902) 889-9250
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Nova Scotia  B0J 2L0, CANADA                      Home  (902) 889-3555

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