Ed: That is true. For my position MONTEVIDEO - URUGUAY Latitude: 34° 54' 38.2" S Longitude: 56° 11' 35.9" W Magnetic declination: 9° 34' WEST Declination is NEGATIVE Inclination: -39° 37' Magnetic field strength: 23116.9 nT regards

Jose Luis Vila CX2AN

----- Original Message ----- From: "Edward R. Cole" kl7uw@acsalaska.net To: "jlv" jlv@fing.edu.uy Sent: Thursday, September 08, 2011 1:12 PM Subject: Re: [amsat-bb] Re: Magnetic North vs True North

At 07:30 AM 9/8/2011, you wrote:

...

True North

tip:

Look for the magnetic north with the compass, read their geographical coordinate in the GPS, use this webpage http://www.ngdc.noaa.gov/geomagmodels/Declination.jsp and calculate the magnetic declination for their place. You will know where this the true north using the magnetic north + / - the degrees of magnetic declination.

Jose Luis Vila CX2AN CX0CFI op.

-----Mensaje original----- From: Luc Leblanc Sent: Wednesday, September 07, 2011 10:07 AM To: amsat-bb@amsat.org Subject: [amsat-bb] Magnetic North vs True North

How i find my north!

At noon always using standard time i pointed the beam in the direction of top tower pole shadow on the ground. Quite simple and accurate enough here.

"-"

Luc Leblanc VE2DWE Skype VE2DWE www.qsl.net/ve2dwe DSTAR urcall VE2DWE WAC BASIC CW PHONE SATELLITE

thanks Jose,

very useful as declination is moving +17min/year here 17deg52min east

I have old aviation maps of the region showing 26-deg declination.

The sun shadow method works only if you know accurately what time solar noon is. For our time zone it is 2202:52 utc (today) which corresponds to 2:02:52 pm local time. So if you used the shadow at 12:00:00 local time you would be off considerably from true north. Of course one hour is due to daylight savings time which advances the clock one hour in summer and the fact that our local time was permanently advanced by one hour for political/business reasons (so we would only be +4 hours from EST in the USA).

This is the reason that one must know true north to orient a sundial.

Sea navigators know they either need to know time precisely to "shoot the sun" and find their location or know true north to determine the exact time of meridian crossing at noon.

73, Ed - KL7UW, WD2XSH/45

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