NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Almanacs, theory and use.
From: Gary LaPook
Date: 2007 Nov 20, 11:36 -0800
From: Gary LaPook
Date: 2007 Nov 20, 11:36 -0800
Gary LaPook writes: the following link had been posted on september 8th to a nomogram which gives you the refraction correction which is easy to use: http://nsg.upor.net/library/altnomo.pdf gl On Nov 20, 11:31 am, glap...@pacbell.net wrote: > Gary LaPook writes: > > Attached is a link to site that will print out a version of the > Nautical Almanac daily pages. For times between the tabulated values > to find GHA you use straight line interpolation, 15� 00' per hour for > the sun and planets, 14� 19' for the Moon and 15� 02.5' for Aires. > > The "v" and "d" corrections at the bottom of the columns for the > planets, the top of the column for the moon and the "d" correction > only for the sun are also used for straight line interpolation for the > declinations of these bodies and for their GHA motion in excess of the > 15� 00' standard value for the planets. ( No "v" correction for the > sun.) the actual Nautical Almanac has interpolation tables included > for every second of time but these are not in this online almanac but > are easy to compute with a calculator. > > Also attached is a link to an online version of The American Practical > Navigator refrence work, go to chapter 19. > > http://www.tecepe.com.br/scripts/AlmanacPagesISAPI.isa > > http://www.i-DEADLINK-com/bowditch/ > > On Nov 20, 3:39 am, Isonomiawrote: > > > 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 -~----------~----~----~----~------~----~------~--~---