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From: Lu Abel (no email)
Date: Tue Jun 07 2005 - 12:19:45 EDT
Frank Reed wrote:
> Where is this world where one crosses oceans without GPS? Are you concerned
> that yours might break down? The best backup for GPS is another GPS.
> Celestial navigation is no longer a primary method of navigation. There are plenty of
> people who want to do it for fun and challenge and maybe, just maybe, for a
> backup in case something happens to the main GPS *and* the various spare GPS
> receivers.
Right on, Frank! I'll bet you'll be crucified for this remark by the
"you can't trust anything with electronics in it" crowd along with the
"it was good enough for Lord Nelson, it's good enough for me" crowd, but
you what you speak is absolute truth. I once fantasied about writing
(say, to this list) a proposal for a new satellite navigation system
which could be unavailable for long periods due to weather conditions,
would give LOPs only for roughly 12 hours a day, and would give fixes
only during very brief periods twice a day -- and then pointing out that
I had described celestial navigation.
> Well sure. You can do that. Consider an alternative: even the most
> enthusiastic students will enjoy being able to get a good position fix on the first
> day of class. So teach lat/lon by noon sun, and then move on.
Here's where I respectfully disagree: In order to teach noon sights,
you've got to teach obtaining the sun's declination from the Nautical
Almanac for any arbitrary GMT, plus calculating LAN (which means the
equation of time), plus calculating time fairly accurately (watch error,
ZDs, etc) (I'm assuming you do not want to tell the student to just
stand there for hours taking observations, but rather want to give
him/her the enjoyment of getting a good position fix with 15~30 minutes
observation. Plus they have to know all about IE/IC, semidiameters,
etc, etc.... Putting it another way, the only thing NOT required for a
good noon sight is LHA! But, to give the devil his due, reduction is a
lot simpler.
Wouldn't a shot on a bright planet at dusk be just as simple as a way of
giving the student the early encouragement? A good sight reduction
form should step the student through the steps, including stepping
him/her through the equations for calculator reduction. (I'll admit
bias -- my very first shot was of Venus at dusk. We took sights and
then adjourned to a local coffee shop where our instructor helped us
reduced our sights. When my LOP came out only about 1-1/2 miles away
from my known position I felt like Christopher Columbus!)
I was going to reply to another of Frank's postings, but I'll include my
ideas here since part of this posting included comments on the
variability of students "getting" celestial: I think one of reasons why
people don't want to learn celestial (ignoring for the moment that today
it's an anachronism) is that it seems so very complicated. But a big
part of this is simply our mysterious terminology. When I open a
celestial class (or even try to motivate folks completing a coastal
piloting course to consider going on to learn offshore navigation) the
very first thing I tell them is that it seems more scary than it really
is because celestial is based on many notions they already know, but
it's obfuscated by arcane terminology. Why, for example, do we speak of
the GP of a body in terms of DEC and GHA instead of L/Lo??
Speaking of the challenges of teaching: I'm an engineer. I've always
lived and worked where there have been a high concentration of
engineers. I've taught USPS's coastal piloting courses for over two
decades. Teaching a mixed audience the concepts of allowing for
currents is always a challenge. The engineers in my class see it
instantly as a simple problem in vector math and are ready to move on;
the others are totally mystified and I have to figure out how to explain
current diagrams to someone who last took high school math 20 years ago
and hated it!
Lu Abel
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