NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Calculators
From: Bill Murdoch
Date: 1999 Sep 02, 11:49 AM
From: Bill Murdoch
Date: 1999 Sep 02, 11:49 AM
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