NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Noonsite using artificial horizon? Did I do it correctly?
From: Bill B
Date: 2014 Aug 25, 18:06 -0400
From: Bill B
Date: 2014 Aug 25, 18:06 -0400
> How I determined LAN- > I do it one of two ways (sans cell phone). Online Go to: http://www.tecepe.com.br/scripts/AlmanacPagesISAPI.dll Click on "Navigator Star Finder" then enter you lat and lon as well as checking to see that the GMT date is correct. Click "submit." On the page that comes up click on "Sun" on the list to the right of the image and it will provide you with the GMT meridian passage (aka LAN for the Sun). It will also provide you with declination, GHA, LHA etc. for the specified time. (Be sure to adjust the GMT time to your time zone.) If you go back to the entry form and enter the time of meridian passage from the above (LAN) and repeat the above sequence you will see Hc, declination etc. for LAN. Nautical Almanac/west longitude * Go to the daily page for the current GMT date. * Locate the GHA closest to but less than your longitude. * Subtract that GHA from your longitude. * Divide the remainder by 15 with a calculator, being certain to convert between decimal degrees and degrees/minutes/seconds during the calculation; or use the arc-to-time table in the rear of the NA. * Add that to the whole hour UT time you used for the GHA and and adjust to your time zone. Example: * Longitude: 86d 14' 54" W * GMT date: 25 August 2014 * Nearest GHA below longitude: 74d 29.3' at 17:00 UT * 86d 14' 54" - 74d 29' 18" = 11d 45' 36" * 11d 45' 36" / 15 = 00:47:02.4 by calculator * 11d 45.6'= 44 minutes + 3 minutes 2 seconds = 47 minutes 2 seconds using NA conversion of arc-to-time table * UT for LAN = 17:47:02 (17:00:00 + 00:47:02) * Adjusted to EDT (-4) = 13:47:02 BTW * There is no dip correction for and artificial horizon (AH) * If you are making the bottom of the reflected limb tangent to the upper limb of the clear glass image, it is a lower limb sight and vice versa. I find limb-to-limb rather than trying to superimpose more accurate for me. Your mileage may vary.
