NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Paul Dolkas
Date: 2013 Dec 27, 14:39 -0800
All-
I haven’t really been paying attention to this thread, but from what I gather, it deals with local variations to the gravity field - direction, rather than magnitude. Is it really true that depending on where you are you can expect to see a significant variation in the gravity vector (say 1-2 arc min) from the theoretical? Seems a lot.
The reason I am asking is that I have always wondered about the practicality of an electronic sextant using a very precise solid state inclinometer, rather than having to manually align the celestial target with the horizon or some surrogate (e.g. bubble). If the local gravity field is that “lumpy”, then this would limit its accuracy.
-Paul
Paul Dolkas
paul@dolkas.net
From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of Greg Rudzinski
Sent: Thursday, December 26, 2013 7:11 PM
To: paul@dolkas.net
Subject: [NavList] In Search of Dip Anomaly
For two days now Santa Ana winds have been blowing here in Southern California. I have been waiting for these exact conditions of hot air over cold water to see if dip anomaly is present.. To check for this a series of sextant observations were made using the natural horizon which were then compared to a series of sextant observations using an artificial horizon. Intercepts using the natural horizon all fell between 3 and 4 NM from GPS. Intercepts using the artificial horizon all fell between 0 and 1 NM from GPS. It appears that 3 minutes of arc of anomalous dip is present. When prevailing conditions return then another series of observations will be made to see if the natural horizon intercepts and the artificial horizon intercepts are in better agreement.
http://en.wikipedia.org/wiki/Santa_Ana_winds
Greg Rudzinski
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