Next message: Frank Reed: "Re: Bubble Horizon Follow Up"
George H wrote:
"I would agree with Howell's view here, not with Frank. Because those
corrections are so very small, and because the inherent accuracy of a
bubble=-sextant (even on a steady platform with a steady hand) is so much
worse than that of a sextant using a sea-horizon or liquid
artificial-horizon, then such temperature / pressure corrections will have
little practical effect on the answer, except under extreme climatic
conditions."
Saying that they MAY be ignored because they have little practical effect is
certainly reasonable. But notice that this would get you in trouble in a
backyard in Denver again. A 15% change in refraction should not be ignored even
with a low accuracy sextant sight. Of course, the Nautical Almanac refraction
tables were never intended to be used at high altitudes. The Air Almanac
refraction tables included a separate entry for altitude above sea level (which is
equivalent to removing the sea level calibration from the barometric pressure).
Also the section in Sue's book is specifically describing artificial horizon
sights which can actually be *more* accurate than standard sights using a sea
horizon. So her instructions to ignore the temperature correction are
definitely incorrect. It's an excellent introduction to celestial navigation, but
unfortunately Sue never had the opportunity to revise it thoroughly.
Frank R
[ ] Mystic, Connecticut
[X] Chicago, Illinois
