View Full Version : Nautical Almanac: Perpetual or 'Long Term' ?
05-05-2006, 06:45 PM
Perpetual Nautical Almanac: Sources for ??
I am interested in simple long term or perpetual nautical almanacs, understanding that is is likely only the sun and stars(Aries) that will be so regular that their tables may be simplified. So far I have found the items listed below, and I have copys of #2 & #3.
I understand that full almanacs are available in computerized/programatic form, but for this discussion I am looking for abbreviated, 'Life Boat' almanacs if you will.
(1) The back cover AP3270 - Sight Reduction Tables for Air Navigation (UK version) contains a 50 year almanac for the sun.
(2) Self- Contained Celestial Navigation with H.O. 208 (John S. Letcher) , contains an 'long term' almanac for 1975-2000.
(3) Bowditch, Vol_1 (1984), appendix 'H' is a perpetual almanac, based on a four year cycle.
Well? how much do you expect on paper?
05-28-2011, 05:09 PM
I was searching for theodolite information (friend wants data on a old one he bought) and by accident found this interesting article/shortstory related to navigation.
Uhm, OK, surveying but same problem azimuth and altitudes calculated using spherical trig and the to us so familiar P-Z-X triangle, discussion on precission and formulas...
the bonus is a PDF of the Bowditch Long term almanac
here is the link
05-28-2011, 10:23 PM
Almanac data for sun and stars valid till 2050
by Dr. Geoffrey Kolbe
It is smaller than a sheet of letter size paper and about 1/2" thick.
Nautical almanac data for the sun and selected stars valid until 2050, plus easy to use, concise sight reduction and altitude correction tables. Plus work forms to make the process even easier. A concise one-book solution for celestial navigation. It takes a few extra steps to get GHA and dec with the Long Term Almanac, since it does it without the usual 10 pounds of reference books, but with practice it takes just a few minutes longer than normal almanac look up.
05-29-2011, 12:21 PM
One can use a Nautical Almanac that is 4 years out of date with satisfactory results. I always kept a set of 4 in my nav bag along with a set of sight reduction tables for air navigation (air tables are much more compact and plenty accurate for sights taken on a small boat tossed about in large seas), so I could grab and run without worry.
The long term NA is a much more elegant solution. I didn't know about those things decades ago.
06-02-2011, 02:47 AM
ah, yes i actually have that almanac, very good and compact, but this is just four pages and accurate to about 2.5' as far as i have seen, together with the excellent sight reduction table made by Henning Umland it is good enough for finding land most anywhere.
here is his two tables the compact is something like 15 pages (manual and legal add another 8)
the larger one is well worht the extra paper, have made very tight fixes with that both at land and sea, only downside (not to great) is loss of accuracy close to 90 and 270degrees.
06-21-2011, 03:20 AM
One can use a Nautical Almanac that is 4 years out of date with satisfactory results.
true Sun and Aries repeat, not exactly but to within roughly 0.75' for sun and 0.5' for Aries, this mean that SHA and the stars declinations and SHA s are within reason for two consecutive four year "cycles" from date on regular NA without additional maths.
beyond 8 years error will increase beyond what I consider reasonable, by saying within reason I mean within 8'
Sun is still within reason for say 12 years but stars...
Capella change in SHA ~1.1'/Year and Atria 1.6'/year, still others -Achernar, acrux, Dubhe, Schedar to name few- change declination slightly more than 0.3' each year these all add to fairly large errors after 8 years.
Sadly moon and planets do N O T ! repeat in such a simple manner, moon especially is wobbling more than smoothly revolving, and as I do lunars, I more or less always have Henning Umlands larger table and NA in the boat, but for easy carry and grab bags the 2000-2050 longterm or Bowditch Longterm+ Hennings compact are hard to beat.
To make time pass I actually have made an updated Bowditch variant (base year 2008) last winter (a 6 month project few lines here and some there), sadly I have not had time to verify it... I added Dip (0.5m-20.5m) and refraction table (90°down to 0°0') and some other minor things and did a check on the SHA and DEC figures of the stars and got them to 3 decimals, also updated all declinations and SHA figures to the 2008 value, also did a update for Sun for 2008-2011.
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