Talk:Magnetic declination

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Contents 1 Total re-write required 2 Navigation equations 3 Definition of Magnetic Declination is in doubt 4 The image is not correct either 5 Fixed "East is Least/West is Best" 6 Grid magnetic angle 7 Animated image is too large

[edit] Total re-write required

This page is badly written, very amateurish, verbose and confusing, it badly needs to be re-written. Frankly, the term 'Magnetic Declination' is a misnomer in itself. It should be Magnetic Variation. This removes a whole layer of confusion. Magnetic Deviation could then be explained perhaps as an adjunct in relation to compasses mounted on vehicles etc. The rest could be much more simply and clearly explained. As it stands, the page is, frankly, gibberish. —Preceding unsigned comment added by 88.111.22.90 (talk) 18:05, 19 January 2008 (UTC)

[edit] Navigation equations

If a easterly deviation is considered positive, and a westerly negative.. shouldn't the equation be standardized to reflect that? Currently it shows a "Compass Bearing +/- Deviation = Magnetic Bearing", but this is ambiguous.. do you subtract a negative westerly deviation or add it? csnoke 18:35, 17 April 2007 (EST)

Too many comments for one day! But this highlights exactly what I mean by "terminological thicket". The "east is least/west is best" stuff is likewise. Can the presentation be simplified? What do professional navigators actually do when on the job? I find it hard to believe any of them are muttering about virgins as they go about their computations -- as this article somewhat suggests(!). mdf 13:19, 13 September 2007 (UTC)

[edit] Definition of Magnetic Declination is in doubt

As it in the article: The magnetic declination at any point on the Earth is the angle between the local magnetic field -- the direction the north end of a compass points -- and true north.

According to FAA, it is the angle between true north and magnetic north. Direction compass points is not magnetic north, because bearing of compass is affected not only by the local magnetic variation but the carrier's own magnetic field as well. —The preceding unsigned comment was added by Natasha2006 (talk • contribs) 18:40, 25 April 2007 (UTC).

See my comment below: the magnetic field of the Earth doesn't care about your difficulties in making the measurement. Rather than confuse the matter, I strongly recommend a strict separation between the field itself, and to how the field is exploited by navigators. mdf 13:08, 13 September 2007 (UTC)

[edit] The image is not correct either

Explanation is the same as it for the definition.--Natasha2006 19:05, 25 April 2007 (UTC)

[edit] Fixed "East is Least/West is Best"

This was backward. A west variation means that magnetic is less than (counter-clockwise from) true.

[edit] Grid magnetic angle

The article claims that magnetic declination is "also known as grid magnetic angle in military circles". However, grid north is a property of the map projection, not the planet: it will be close to, but not in general exactly "true north". Various checks on the net confirm this view, so I'll be removing it in a day, unless someone objects.

I'll also say that over the year or so since I last edited this, a fair amount of confusion has been added here. This no doubt reflects the "terminological thicket" that surrounds a great deal of the art of navigation. Perhaps some simplicity may be restored by isolating all the navigation stuff, either in this article, or moving it all to another. After all, "magnetic declination", as defined in the intro here, is a component of the local field, unsullied by whether or not the guy making the measurement is wearing an steel watch, and wants to get from where he is to where he wants to go (see: http://gsc.nrcan.gc.ca/geomag/field/magdec_e.php for more on this distinction). mdf 13:02, 13 September 2007 (UTC)

Grid Magnetic Angle (GMA) and Magnetic Declination are two completely different things. GMA is the difference between Grid North and Magnetic North whereas Magnetic Declination (AKA Magnetic Variation) is the difference between True North and Magnetic North. The difference between Grid North and True North is known as Convergence. —Preceding unsigned comment added by 84.139.36.214 (talk) 12:16, 24 May 2008 (UTC)

[edit] Animated image is too large

The animated map of changes over time is a very large file: it weighs in at 3.4MB. Can I suggest we put a link to the Commons instead? It just doesn't seem sensible causing users to load such a large file as part of the default page. El T (talk) 12:11, 28 December 2007 (UTC)