NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Almanacs, theory and use.
From: Mike L
Date: 2007 Nov 20, 03:39 -0800
From: Mike L
Date: 2007 Nov 20, 03:39 -0800
We live in Scotland and my mother lives in England, so I thought it would be pretty simple to prove to my kids using a sextant that the world was spherical - so I bought an EBBCO on eBay. Whilst I've proved to myself I can use a sextant to find out where I am, I'm still to convince the children either that you can, or that you would want to. I started by using some software into which I put the time, approximate longitude, latitude and sextant reading, and (after working out I had to subtract half the sun's diameter) I finally got something average on our location on average about 3 miles from our location. Unfortunately, as far as a kid is concerned, if you have a PC, you may as well look up google/streetmap rather than waste time with a sextant, so I need to find a PC-less way to find out where I am. So, using a bit of trig (with some software from the web) I created my own single-page weekly tables (the sun don't shine everyday!), giving altitude and direction of the sun for a given location for each minute of the day. This allows me to create a table for any given place which most children who can add two digit numbers, and use a ruler/protractor could use by themselves (with instructions) to plot a line giving their location (to within 10miles I hope!), which if repeated twice in a day should give an "exact" location. Now, I know how my "Almanac" works, but even having figures for every minute of the day, for a known location and interpolating results for seconds, I will still be pushing it to get tabular errors less than 1'. From what I have been able to discern about real almanacs they contains a fraction of this information with only hourly figures for every location in the world. Although, I've downloaded a few worksheets to "calculate" the figures, I can't understand how these are used (I neither have a worked example, nor do I have an almanac, nor do I have a theoretical explanation for the tables - but I don't see that as a fundamental problem!) Surely getting from these figures in the Almanac to one at any time for a particular location but involve some complex trigonometry and rather hectic sinusoidal interpolations - neither of which are apparent on the worksheets! What I really want to know is how my "almanac" relates to a real almanac, and how, could and should I make my "almanac" more like a real almanac and still have it useable by children? I've tried searching the internet, for any explanation of how to use an almanac (with the theoretical background) - any help would be greatly appreciate (remembering I am not familiar with SHA, GHA, and whilst I learnt spherical geometry at University, I'm a little rusty) --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to NavList@fer3.com To , send email to NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---