NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Coriolis vs Noon curve correction
From: Jeremy C
Date: 2009 Apr 26, 07:04 -0700
From: Jeremy C
Date: 2009 Apr 26, 07:04 -0700
> The correction of the noon curve for motion is nothing more than the correction for a running fix. Imagine solving a noon curve set of sights by plotting LOPs. You would have to advance the earlier sights to "catch up" to the later ones. Since all of the LOPs are nearly parallel (the Sun's azimuth changes by a relatively small angle), this advancing is equivalent to changing the observed altitudes by an amount proportional to speed and elapsed time. Try it on paper if you need to convince yourself. > > -FER What I find interesting is that much of this talk centers around these two points: 1) the motion of the ship, especially in a N/S direction, and 2) the change in declination of the sun during the sight process. When I use the computer program on the ship for these sights (SkyMate Pro), I tell the computer the time I want the fix calculated for (I input either LAN or the nearest half hour), as well as the course and speed of the ship. Assuming that the DR track is reasonably accurate, the lines are calculated, taking into account the varyed declination, and automatically advanced or retarded, taking into account ship's motion, to give me the 95% probablitly fix. I then compare this with the exact GPS reading taken at that minute to see what kind of error I am getting. With the sun and Venus, I consistantly got less than 1' of error in both Latitude and Longitude, and slightly more with the moon. I am scheduled to take a very LONG ocean passage this next tour on my ship, so I intend to do quite a bit of Celnav during it. I will try to "publish" a Nav journal on here when I am through. I intend to try this method over a wide range of latitudes and Northerly declinations, as well as common sights and other exotica (expect numerous lunars as well). Jeremy --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---