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Alex wrote:

> Today I made my first observations with my new MkIXa
> bubble sextant (purchased on E-bay for $41).

With a lighted bubble sextant and a stable platform, twilight is no longer a
limitation for star sights.

Most texts use upper transits of the sun to derive latitude directly, or
Polaris.  Despite lower availability, why not other stars etc.?  No pole
star in the southern hemisphere to rely on. And why no mention of lower
transits of circumpolar bodies for direct latitude?

If trying to pull longitude from a sun transit, the exact time of transit is
problematic by altitude, so we take sights before the expected transit and
after and plot. Or take one perhaps 15 minutes before expected transit and
then match that Ho after transit and split the time to determine transit
time.  That requires a perfect observation on the front and backside, as
well the problem of declination changing over a period of 30-40 minutes time
(albeit about noise given the system resolution).  Stars have a relatively
stable declination, but the viewing period with a conventional sextant would
be a problem.

Why not combine the best of all worlds?  The problem with a time site that
gives you longitude directly is knowing your latitude.  It has been said, "A
good sailor always knows his latitude."  Yet the basis for the discovery of
Sumner's celestial LOP was the fact he was not sure about his latitude. Pull
latitude off Polaris or another transit, and do a time site from a body to
the east or west almost simultaneously.  Almost nstant lat and lon.

I may have reinvented the wheel here, but it was fun to think about.

Bill


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