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Subject: Re: Calculators
From: Bill Murdoch (WSMurdoch@XXX.XXX)
Date: Thu Sep 02 1999 - 13:49:27 EDT
I guess my first point is that astro navigation calculators run from $10 trig
function calculators to Pentium IIIs. All of them are useful. The first $10
replaces several pounds of sight reduction books by solving the cosine
formula. The next $25 will get you a solar almanac and replace the dip and
refraction tables along with the pencil needed to do the sums to reduce a sun
sight. The next $50 will buy enough calculator to replace all the other
information in the Nautical Almanac. The last $2000 makes it all very slick.
There are good reasons for stopping anywhere along that path; especially in
the days of GPS when astro is basically a hobby.
My second point is that programming a calculator (or computer) is for some
people fun. Sure, it is easier to buy a Celesticomp, Palm Pilot or PC, load
in a program, and go to it. But, there is a sense of accomplishment in
doing it yourself. The easiest path may not be the most rewarding - it is
easier, cheaper, and faster to fly from Charlotte to Marsh Harbor than to
sail down from Beaufort, but some prefer to sail.
My third point is that life is about learning. Learning how to take a sight.
Learning how to reduce it. Learning how to clean and care for a sextant.
And, learning how all those numbers in the almanac are calculated. Almost
every JN student asks where the numbers in the almanac come from. Programing
your own astro calculator can be a path to that answer.
I agree with you, the sun is easy. After making the conversion of years,
months, days, hours, minuets, and seconds into a single measure of time,
after handling the data sight data input and the output, and keeping an
accuracy of 0.1', about this much program memory is needed to calculate
almanac data in a TI calculator:
Aries - 75 bytes
Sun - Aries plus 700 bytes
Moon - Aries plus 2000 bytes
Planets - Aries plus Sun plus 600 bytes plus for
Venus - 600 bytes
Mars - 1000 bytes
Jupiter - 1500 bytes
Saturn - 2000 bytes
92 stars - Aries plus 2500 bytes
But, the sun is also the most useful body. You may need no more. (It is a
shame the moon's motion is so complicated. It woudl be a good second body.)
Bill Murdoch
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