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On Apr 10, 2005, at 7:32 PM, c roberts wrote:

> In postings on this list , altitudes and azimuths were required for
> accurate calculations of distances between bodies. How can
> precomputed lunar distances be done as has been done for centuries??
> It would seem that almanac GHA and DEC are the only data available.
> This same calculation would be used for inter stellar distances for
> checking sextant calibrations. It has been said that the values in
> Bauer's book are wrong. In the lunar distance calculations this value
> which is used to proportion for GMT is calculated. Can precomputed
> values be used to avoid this ?
>
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GHA and DEC are used to precompute lunar distances or other distances
between bodies.  Altitudes and azimuths don't enter into the
calculation.  Computation of distances on the hour for interpolation to
minutes and seconds is still a component of methods of determining GMT
from lunars.  The distance computations can be done beforehand,
precomputed, or as part of the process of clearing a set of lunar
distance observations.

Refraction is critical to clearing both interstellar and lunar
distances.  The mistake Bauer made in the table in his book is that he
did not account for refraction.  That, of course, would not be possible
without knowing one's position.

Refraction is dependent upon altitude, and altitudes either have to be
computed or measured to determine refraction when clearing lunars or
interstellar distances

George Huxtable gave a method suitable for electronic calculator using
"Young's Method."  Frank Reed gave one of the "approximate" methods.  I
believe both these methods are linked or presented on Arthur Pearson's
website
.

Fred

   

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