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Fred,

>
> As indicated in a previous post, I have no idea how Meeus' formula was
> developed.
>

Meeus gave in his book the formula provided by G.G. Bennett. To my
understanding this formula has no direct meaning, except that it delivers in
form of a simple expression the refraction values within the full range of
0? to 90? with great accuracy, this on the base of the apparent altitude.
Meeus added in his book his own (simmilar) equation for the inverse problem,
i.e. for calculating the refraction when the physical altitude of the object
is known.

There do exist also other formulae for calcuating refraction. Usually they
tend to be only exact within a certain part of the altitude range.

Marcel

   

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