[TowerTalk] Magnetic declination vs variation: USGS COMMENT

LYN designserv@ipass.net
Sat, 14 Nov 1998 20:13:15 -0500

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Date: Fri, 13 Nov 1998 15:50:58 -0500
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Subject: Re: Magnetic declination vs magnetic variation
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In response to your November 13 message to USGS:

The "Geodetic Glossary" of the NOAA/NOS/National Geodetic Survey defines the term this way:
Declination, magnetic     #The angular direction, east or west from the north branch of the celestial meridian, of magnetic north as determined by the positive pole of a freely suspended magnetic needle that is not subject to any transient, artificial disturbance.#

In nautical and aeronautical navigation the term variation is used instead of declination, and the angle is called variation of compass or magnetic variation.  Except for usage in navigation, magnetic declination is not synonymous with magnetic variation, which refers to regular or irregular change with time of magnetic declination, dip, or intensity. [end quote]

Diane Brittle
USGS Earth Science Information Center

>Date: Thu, 12 Nov 1998 18:22:39 -0500
>designserv@ipass.net would like information/assistance on the following:
>In your paragraph:
>To use this bearing, you must compensate for magnetic declination. If the
MN arrow on the map magnetic      declination diagram is to the right of
the true north line, subtract the MN value. If the arow is to the 
>left of the line, add the value. 
>Is the word "delination" correct?  Shouldn't it 
>be "variation" 


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