[TowerTalk] Direction Finding
Guy Olinger, K2AV
Sun, 12 Mar 2000 21:47:25 -0500
The necessity with using shadows to grab north is the calculation of
*True Solar Noon* for one's particular position on a given day. Have at
look at the web page http://aa.usno.navy.mil/AA/ which will print out
the solar angles for a particular day for a particular position, in 1
minute intervals if you wish.
This is needed because the earth's orbit is not circular and the degrees
swept in the heavens by the earth's position as seen from the sun vary
according to the earth's velocity in it's orbit, which is greater when
nearest the sun and slowest when farthest.
So not only does "noon" vary by longitude, but also by subtle
particulars of the earth's orbit. The printout from US Naval Astro
Applications calculates all that and gives you a time which also avoids
problems with various definitions of "sunrise" and "sunset".
I was able to place a 20 foot string on the ground at true north which,
when compared with my expensive compass, showed an 8 degree offset with
magnetic north at my location, rather than the 5 degrees I had set it,
from what turned out to be an obsolete table. Finally found something on
the net which confirmed the new offset.
I had become suspicious when unable to sight my property lines with the
- - . . . . . . - - . . . . - - . . - . .
Apex, NC, USA
----- Original Message -----
From: Pete Smith <email@example.com>
Sent: Sunday, March 12, 2000 3:08 PM
Subject: Re: [TowerTalk] Direction Finding
> At 12:58 PM 3/12/00 -0700, Stu Greene wrote:
> >This subject comes up time and time again. We're going to get bombed
> >shadow theories, but what's wrong with using the North Star (Polaris)
> >northern reference? It doesn't move more than a degree off true
> >is visible in most of the Northern Hemisphere.
> Sure, but it's equally true (and somewhat easier) to calculate the
> that is exactly halfway between local sunrise and local sunset (from
> newspaper), and look at the shadow of your tower -- it will point true
> north at that time.
> Thanks to W3LPL for my first introduction to this one.
> 73, Pete Smith N4ZR
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