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#81210 - 12/23/06 02:52 PM Why does my compass point South ?
TomSwango Offline
Journeyman

Registered: 10/26/02
Posts: 67
I may be crazy but last year I put all of my compasses side by side and noticed that two appeared to point south instead of north. So I threw them away.

Well last week while in Big Bend National Park I noticed that when I laid out four of my compasses one of them again pointed north.

Since this is probably the third compass I have found doing this and now one of the compasses is pointing south that I assume was pointing north last year I am courious what is happening.

Also all of the crazy compasses have been the small ones like you find in whistles or on zipper pulls with a thermometer etc. All of my larger base plate compasses appear to be OK.

Has anyone else experienced this? Am I doing something wrong? Am I crazy or just moderately incompetent?


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#81211 - 12/23/06 03:17 PM Re: Why does my compass point South ?
oldsoldier Offline
Old Hand

Registered: 11/25/06
Posts: 742
Loc: MA
Its entirely possible that they have had their magnetics screwed up due to be close to metal or something. Small ones arent very accurate. Also, did the liquid inside dry out? Without that to dampen the needle, it may be very inaccurate. Lastly, cheap compasses are cheap for a reason. The generic zipper pull ones twnd not to last very long, in my experience. I carry a small Brunton button compass in my PSK, but, going out into the woods, I always have my military lensatic compass. That is extremely accurate, and, for whatever reason, its the only one I understand (I'm not all that smart sometimes). I had, until recently, depended on my Suunto watch for a backup compass. Until, of course, I needed it, & found out it wasnt accurate either.
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#81212 - 12/23/06 04:40 PM Re: Why does my compass point South ?
billym Offline
Addict

Registered: 12/01/05
Posts: 616
Loc: Oakland, California
You cannot put compasses "side by side" this throws off the magnetic fields.
The way I test a compass is place it on on a flat surface (non-magnetic) and hold the other compass a foot or so above it and align the arrows.
Remember to keep them apart.

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#81213 - 12/23/06 07:59 PM Re: Why does my compass point South ?
IzzyJG99 Offline
Geezer

Registered: 02/05/05
Posts: 5029
Your compasses were fine. If you line them all up their magnetic fields are gonna screw with one another. Alone they work fine.
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#81214 - 12/23/06 08:09 PM Re: Why does my compass point South ?
JCWohlschlag Offline
Some guy who wandered in…
Old Hand

Registered: 11/26/06
Posts: 724
Loc: Dallas, Pennsylvania, United S...
Basically, this is happening because you are putting two or more compasses in close proximity to each other. The needle on a compass basically is a magnet. The north side of the compass needle is actually the south pole of the magnet, which is why it is attracted to the Earth's north pole. (Remember: Opposites attract with magnets.) The reverse is true for the south side of the compass needle, which is actually the north pole of the magnet and is attracted to the Earth's south pole.

Now, what happens when you put two magnets really close to each other? Those two magnets will pretty much disregard the relatively weak magnetic field of the Earth and they will simply orient themselves opposite one another. One compass needle's magnetic south pole (marked "north") will attract the other compass needle's magnetic north pole (marked "south"), and you will have two needles pointing in opposite directions.

Solution… Move the compasses a ways apart from each other (and from nearby metal objects, other magnets, etc.) and they will again both point the way they should.
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#81215 - 12/24/06 05:04 AM Re: Why does my compass point South ?
aardvark Offline
Member

Registered: 03/11/06
Posts: 109
Loc: So. California
Normally i don't nitpick but having studied physics i felt i should add to this discussion. The earth's north magnetic pole is actually magnetic south. So you are correct that the opposites must attract with regards to a compass needle and the earth's magnetic field. However, it is convention that the compass needle is considered not reversed and all the stuff with the right hand rule in electromagnetism follows from this.
It won't matter anyway, the field is going to wander around and reverse itself in a hundred thousand years. <img src="/images/graemlins/smile.gif" alt="" />

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#81216 - 12/24/06 06:43 AM Re: Why does my compass point South ?
JCWohlschlag Offline
Some guy who wandered in…
Old Hand

Registered: 11/26/06
Posts: 724
Loc: Dallas, Pennsylvania, United S...
Ah! Thank you for correcting me on that! Checked it out on Wikipedia, and I just learn something new and interesting every day. And here I though it was called north because that's where magnetic north was.

So it seems that compasses are correct and it's just the Earth that's screwed up? <img src="/images/graemlins/laugh.gif" alt="" />
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#81217 - 12/24/06 06:20 PM Re: Why does my compass point South ?
Old_Scout Offline
journeyman

Registered: 11/03/06
Posts: 95
Loc: Delaware
Quote:
However, it is convention that the compass needle is considered not reversed . . .
I'm glad you mentioned "convention." A lot of things concerning navigation are by convention. As a cartographer I can assure you that "North" was not always "up." Many older maps have what we call the North Pole at the bottom of the sheet! If you think about it, it really doesn't matter since all the really important relationships between maps and compasses are independent of orientation on a piece of paper. It's orientation in the "real world" that really matters. To be perfectly correct your compass doesn't really point "at" anything (like the so-called magetic north pole) but, instead, aligns itself with the local magnetic fields orientation where you're standing. As you move around the earth to various locations and plot these lines of orientation they are referred to as isogonic lines of declination meaning a line on the earth where the variation of the compass from true north is the same all along the line. The one isogonic line where the variation from true north is exactly zero (0) is known as the agonic, or a line describing all those points on the surface of the Earth where true north and magnetic north are the same (for the time being!) Also, bear in mind that the magnetic poles of the Earth are constantly moving (albeit slowly). Pole Drifting
I like the explanations given to your dilemma as being most likely correct. One other, more remote, possibility is that the faulty compasses were stored near some fairly powerful source of magnetism for a period of time and the needles were re-magnetized. This could be either a metallic magnet or possibly, an electrical field, such as a motor.
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"Be Prepared" "For what?" "Why, any old thing!" B-P

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#81218 - 12/25/06 03:59 AM Re: Why does my compass point South ?
Seeker890 Offline
Journeyman

Registered: 06/19/06
Posts: 93
Loc: Central Ohio
If the compass needle does not re-orient after seperating as has been suggested, perhaps it has been in too close proximity to a strong magnet? I had changed the polarity of my old scout compass needle in my youth with a magnet. It can be re-oriented back to original by re-magnetizing the needle with a magnet. I don't recall which end I had to "trap" with the magnet to make it point correctly, but a little trial and error will make it right. You might want to look at your storage if the needle was truely magnetized incorrectly.
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#81219 - 12/30/06 10:23 PM Re: Why does my compass point South ?
Brangdon Offline
Old Hand

Registered: 12/12/04
Posts: 1161
Loc: Nottingham, UK
Perhaps they were Australian magnets.
<img src="/images/graemlins/grin.gif" alt="" />
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