|
|
|
|
|||||
|
||||||
From: Frank Reed (no email)
Date: Sat Jun 04 2005 - 20:42:25 EDT
George H wrote:
"But why, in this age, does a mariner still ask for separate determinations
of latitude and longitude? It's as if we were still stuck in the early
1800s, and Sumner and St Hilaire had never invented position lines."
A little ironic, no?
Why, in this age, does a mariner still ask how celestial navigation works?
It's as if we were still stuck in the 1970s, and GPS has not been
commercialized yet.
Or how about this variant:
Why, in this age, does a mariner still ask how lunar distance observations
might work? It's as if we're still stuck...
Well... you get the idea!
And:
"Why not just measure two altitudes of the Sun, at any old times, but times
which
are well separated so that the Sun's azimuth has changed significantly
between them. Then draw a couple of position lines from some assumed
position, allow for vessel's run in the interval, see where they cross, and
that's where you are, in lat and long. Simple as that. Applies to any sight
of any body at any time: a universal way of doing the job. Who needs
anything different? "
That's a ten-week course of work and frequent repetition required to keep up
the skill. By contrast lat/lon by noon sun is something that can be learned
and re-learned in an afternoon. It's not quite as accurate (does that matter?
depends on what you're trying to achieve) as full-blown celestial navigation,
but fewer and fewer students are interested in toiling over the details of
the Nautical Almanac's interpolation tables and the tedious study of H.O. 229
or other sight reduction tables. They wanna play with their sextants and
figure out where they are in the fewest possible steps (just in case something
bad happens to GPS). Of course, there are still plenty of others who want to
learn the complete methods of "apex celestial navigation" because that suits
their personal goals and interests. We're even getting to the point where
people are studying it out of historical interest...
-FER
42.0N 87.7W, or 41.4N 72.1W.
www.HistoricalAtlas.com/lunars
|