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Ken Gebhart wrote:

> Regarding Joel Silverberg's talk on latitude by double altitudes, I
> asked the question of how this works on the two days of equinoxes.  On
> these days there will be 12 hours between the zero altitudes of
> sunrise and sunset at all latitudes.  So how could a unique latitude
> be determined?


Ken,

You are right that the method falters if both observations are taken
with the body (-ies) at the prime vertical. But this is nothing specific
to either the double altitude method nor to the time of equinox. It is
simply due to the fact that the altitude of a body in the prime vertical
provides zero information on your latitude, no matter what your sight
reduction method be and at what time of the year or day the observation
be taken.

But the double altitude method to find latitude is not meant to be used
in that extreme way: One is supposed to take two observations with a
REASONABLE hour angle between them, say 60 to 90 deg. That always works,
also on the days of equinox. If the hour angle is 180 deg, there is no
doubt that some triangles degenerate and the method - and any other one
to find latitude - becomes useless.

Did I understand your question and did I answer it?

Herbert Prinz

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