NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Coriolis vs Noon curve correction
From: Frank Reed
Date: 2009 Apr 25, 20:46 -0700
From: Frank Reed
Date: 2009 Apr 25, 20:46 -0700
Peter Hakel, you wrote: "The Volume 1 of HO 249 tables intended for air navigation includes "Table 1: Altitude correction for change of position of observer" and "Table 9: Coriolis (Z) correction" table. This just occurred to me and I haven't thought about this in detail yet. Could these tables be of any use for the noon curve construction on a vessel moving during the half-hour or so before and after LAN? I realize that ships do not move as fast as aircraft, but it looks like our aviator friends have already considered and solved this problem, so perhaps we can learn from them. The only difference should be in the magnitude of the ground speed, which should make the corrections even easier on more slowly moving surface ships." The Coriolis correction is required because the sextant is accelerating in the aircraft. This causes the bubble to indicate something different from the true vertical. This correction is best categorized as a "sextant correction" like index correction. It is a property of the instrument and its behavior when moving. 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 --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---