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George has a point about calculated altitudes. But the explorers and
surveyors of the past routinely left the altitudes to be calculated. They
were using a different kind of nautical astronomy and a different kind of
Nautical Almanac. It was only in the twentieth century, with the advent of
the GHA Almanac, that navigators came to need accurate Greenwich time to work
their observations. I've tried to show how the old system worked in a series
of papers on Lewis and Clark's observations, published by the Navigation
Foundation.

But the point I particularly want to make is that people should observe
distances wherever they are, without taking the time or going to the trouble
of dealing with an artificial horizon. That way they will take hundreds of
observations, not just one or two, and they will become familiar with their
sextants.

Artificial horizons are an important topic on their own. I've read some good
advice, and done a bit of experimenting, but would not take many observations
if it were mandatory to set one up every time.

Haven't tried it yet, but I think we can figure out how to use our present
Almanac the same way the old navigators used theirs.

Bruce

   

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