NavList:

Hewitt wrote:

"Is the +2.1' 4-year correction to GHA Aries mentioned by Gary based on
new astronomical work? I've always used +1.84'. Kolbe's long-term
almanac does also.  -Hewitt"

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I was wondering about that myself. I have used Kolbe's almanac and it is easy to use and produces accurate data. I have compared his data with my N.A. and with the data on the Naval Observatory website and I am impressed with its accuracy. Its use is similar to the long term almanac in H.O. 249 but produces data to one-tenth of a minute compared to H.O. 249's one whole minute precision.

So I decided to investigate the discrepancy between Kolbs's 1.84 constant and the 2.1 constant I posted. I am working with the assumption that the Naval Observatory website is authoritative.

http://aa.usno.navy.mil/data/docs/celnavtable.php

Looking at four year cycles, 2000, 2004.....2032; 2001, 2003.......2033; etc., I found that there was not a constant difference per cycle but varied from 1.5 to 2.2. Looking at eight such cycles for each starting year (2000, 2001, etc.) since the Naval Observatory website only goes to 2035, the average change, sorted by starting year, varied from 1.85 to 1.90. The average of the averages is 1.87, very close to Kolbe's value. Since his almanac goes all the way to 2050 it is likely that his average change came from considering this larger data set. Kolbe's almanac produces quite accurate data, certainly good enough for navigation, using his long term average constant for GHA Aries. It doses appear that  a slight improvement in accuracy could be made if you have access to the N.A.s for the the two years in question or to the N.O.'s website and you calculate the constant to use with his almanac.

I hope nobody construes this as a criticism of his fine almanac since it provides very accurate data for navigator's at sea who do not have access to a new N.A every year or to the Navy website. I used his almanac on my recent Atlantic crossing and I am quite impressed with its accuracy and ease of use.

gl




Hewitt Schlereth wrote:

Is the +2.1' 4-year correction to GHA Aries mentioned by Gary based on
new astronomical work? I've always used +1.84'. Kolbe's long-term
almanac does also.  -Hewitt

On 12/8/09, Greg Rudzinski <gregrudzinski@yahoo.com> wrote:
  

Thanks Gary and Frank,

 I will be using my 2006 Nautical Almanac for 2010 Sun observations
 with no corrections and be within .5 MOA (good enough). For stars the
 plan is to photo copy the online Nautical Almanac for
 1/1/10,3/1/10,6/1/10,9/1/10 and use the star SHA and declinations plus
 a 2.1 minute GHA aries correction which should get me within .5 MOA
 (good enough). Looks like I'm out of luck for the Moon and Planets
 though. Any ideas on how to compensate the Nautical Almanac Polaris
 table ?


 Greg


 On Dec 7, 5:10 pm, Greg Rudzinski <gregrudzin...@yahoo.com> wrote:
 > Any opinions on using a Nautical Almanac that is four years out of
 > date? I bring this up because there are old almanacs available on
 > Amazon.com from $2 to $10.  New Nautical Almanacs have gotten
 > expensive so my plan is to use a 2006 for the upcoming year 2010.

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