Question about compass

[Guest Keon]

The dude in the store told me that in the southern hemisphere, the N-arrow on my compass will point to the South Pole. I believe this is completely wrong, of course..

 

It made me smile all day .

 

I also bought an eTrex and I'm planning to do some stash hunting and maybe place my own stash here in Belgium.

 

Greetings!

[Guest ScottJ]

Not true. However, compasses DO have to be specifically manufactured for either the Northern or Southern hemisphere, and a compass designed for the wrong hemisphere won't work properly (although it won't point 180 degrees from correct!) The reason has to do with magnetic "Dip".

 

Scott

[Guest BigFig]

So, do the toilets really swirl backwards down south?

[Guest Keon]

With a normal compass and the "moving compass" on my eTrex, I'll be fine I guess. I'm leaving for South Afrika is three weeks so that's why I was thinking about that problem.

 

And about the toilet water swirling the other way around: You bet I'll check that out!

[Guest robanna]

your compass will be useless in SA. It is two or three magnetic zones away. I only know of one compass right now that will work in all 5 zones and that is the Suunto MC-1G.

 

What happens is the neddle gets pulled down (as if you had tilted it). This is called inclination. The MC-1G has the neddle and the magnet separate so the magnet can tilt and the neddle stays horizontal.

 

My suggestion is to buy one for that zone (3 or 4, depending on where you are going in SA) or buy one there.

 

PS I have pix of a tolet in Fiji if anyone is interested.

 

[This message has been edited by robanna (edited 03-08-2001).]

[Guest Keon]

I'm interested! Show me the compass! :-) My email is keon@pandora.be

 

But I think I won't need that compass because with a car, an eTrex and a few good maps, i should be able to track my position. Anyways, the only problem will be finding the car after a long hike...

 

Thanks for the input

[Guest BigFig]

You'll need that map and compass if your GPS quits. Just a bit of insurance ....

[Guest BigFig]

Robanna:

 

What's this inclination zone stuff? I know about inclination, but didn't know there were zones?? Where can I find more information?

[Guest BigFig]

And, I'd like to see the "dirty" pics

 

Couldn't you just tilt the compass so the needle would float??

[Guest Candy K]

I'm new to navagation.

I just bought my first compass...but don't really know how to use it..read it.

Can anyone recommend a good beginners book or better yet web sight.

Thanks,

CK

[Guest mcb]

I have been using a compass for navigation for many years and I have never heard of needing a different compass for the southern hemisphere. I think you should check your sources on that one ScottJ. I have heard of using a compass that can measure magnet "Dip" when you are very close to the magnet poles but if I remember right you have to be very close (~50 miles) to the magnetic pole to use a "dip" compass like that. Otherwise a compass is a compass and as long as you realize that the compass points to magnetic north and not true north and one must compesite for this when using maps. If Im wrong I would love to see documentation on the difference between a northern hemisphere and a southern hemisphere compass.

[Guest peter]

quote:

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Originally posted by mcb:

I have been using a compass for navigation for many years and I have never heard of needing a different compass for the southern hemisphere... If Im wrong I would love to see documentation on the difference between a northern hemisphere and a southern hemisphere compass.

---

 

The difference is just in how the compass needle is weighted so that it spins freely when the compass is held level. If the compass is made for a greatly different latitude, then you may need to tilt it to get it to read properly. See the discussion for one Brunton model at: http://www.stanleylondon.com/COMPBRUN.HTM and REI's description at: http://www.rei.com/reihtml/LEARN_SHARE/camp/howcomptop.html (in the section on 'Compass Tips and Terminology.'

[Guest Cape Cod Cache]

The Earth is a big magnet, north is north and south is south PERIOD. Re-read your basic Earth science book. If a different compass were needed for the north and south hemispheres, then a compass would be useless at the equator.

[Guest Keon]

quote:

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Originally posted by Cape Cod Cache:

The Earth is a big magnet, north is north and south is south PERIOD. Re-read your basic Earth science book. If a different compass were needed for the north and south hemispheres, then a compass would be useless at the equator.

---

 

That's exactly what I was thinking. But the thing about dip at very short distance of the magnetic poles sounds true... When I'm out there on South Africa, I'll search north with both my compass and my GPS, just to see what declination I get there .

[Guest bob_renner]

Cape Cod,

 

You're only thinking in 2 dimensions. You need to think in 3 dimensions. The lines of magnetic flux all point to the magnetic poles, but they are NOT parallel with the ground (except at the equator). At northern latitudes the lines (north pointing) are pointing slightly down the further north they go. The compass needle red end will dip down. At southern latitudes, the lines (north pointing) are pointing slightly upward. the compass needle red end will point up. Therefore the needles in compasses must be balanced for the zone in which they are to be used. This balancing (or actually unbalancing) negates the non-level magnetic lines of force, and the end result is that the needle floats level.

 

The following is a quote from the web site of Silva, one of the largest makers of compasses:

 

http://www.silva.se/outdoor/index.htm

 

Balancing

Compasses for use in areas South of a line drawn roughly through the Mediterranean, have to have the needles specially balanced during manufacture. SILVA compasses are balanced for five magnetic zones. For information and/or advice - about any aspect of navigation or related equipment contact SILVA.

 

Bob Renner

[Guest Uplink]

From http://www.wide-screen.com/Pages/suunto_TechInfo.html

"The horizontal and vertical components of the earth's magnetic field vary considerably in different locations. For this reason Suunto compasses are balanced for 5 different zones. Each zone requires that the compass you use be calibrated differently. As seen from the map, the zone boundaries do not follow a mathematical pattern. They are just as complicated as nature itself. When the regional differences are minimal for a particular country, the whole country is included in the same zone. If the compass is used in an adjacent balancing zone, many compass pointers will tilt only slightly, however, the farther a compass is used from its correct zone, the more its pointer tilts. In extreme cases, the pointer will stick. For this reason it is extremely important to know in which zone a compass will be used.

All compasses from Wide Screen Software are calibrated for use in the Northern Hemisphere. (Zone 1) Compasses for other zones by special order only."

[Guest n1niq]

This is very interesting. I have been collecting compasses for a while now and never heard of this before. Then in the last few days I've seen three references (including a descripition of a Suunto compass)to this phenomenon. I'll have to order a compass from Austraila for my collection!

[Guest Cape Cod Cache]

I stand by my statement, North is North South is South, but in this case magnetically. I have the same compass on my boat that has been from Nova Scotia to the Equator. I keep it set to magnetic North, and get the local deviation to true from charts. As far as this 'Dip', marine compasses are internally gimbaled. One might give a try of a 'hand bearing' compass. A pistol grip with a marine compass on top, point at what you want a bearing from, and voila ! instant Magnetic bearing. Cost from $30 up.

[Guest peter]

Yes, I agree that your marine compass will work fine in the southern hemisphere. So will the Ritchey compass on my boat which is also gimballed to allow for some rolling or heeling of the boat - and this gimballing lets it turn smoothly despite magnetic dip.

 

But my Silva and Suunto hiking compasses are designed for the mid-northern latitude range and will not spin freely if held level while in the southern hemisphere.

See my previous post for a pointer to more details given at REI's website.

[Guest JasonW]

quote:

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Originally posted by Keon:

And about the toilet water swirling the other way around: You bet I'll check that out!

---

 

If you can get near the equator you can try it - I did in Kenya. I took a large basin with me and 6 gallons of water - the equator is clearly marked btw.

 

Stood about 20 yards north and watched the water swirl out in the conventional way, although it did only slowly start to swirl.

 

Moved to the equator itself (ok maybe the line on the the groud isn't that accurate) and it basically dumped out vertically.

 

Moved 20 yards or so south and the water did swirl out the other way about.

 

Big waste of 6 gallons of water in a hot place ? Maybe, but it had to be done

[Guest od Cache]

Keon,

are you thoroughly confused now? I should have worn a fire-proof suit for this. Compasses are pretty personal, I use a Boy Scout unit thats 20 years old for land use. If I used a compass and took a course, there isn't a place within a 100 miles that I could get lost. Find what suits YOU.

[Guest daviskw]

From the Silva website.

 

Magnetic Inclination And

Compass Needle Balance

 

Lines of magnetic force vary from vertical at the magnetic poles, to horizontal near the equator. Consequently, one end of a magnetic needle has a tendency to dip down in areas that lie between the poles and the equator. Silva reduced this tendency by placing the center of gravity below the pivot point of the needle. Also, the needle of each compass is counterbalanced for the middle of the magnetic zone where it may be used. Silva compasses are balanced for the five magnetic zones. The zone setting is marked on the reverse side of each Silva compass (MN). A compass needle may show a slight tendency to dip in an area between two zones.

Butch

[Guest ScottJ]

MCB: Check my sources? I AM my source. In all seriousness, I'm not making this up. Most compasses require specific balancing for the magnetic zone in which they'll be used. You've probably never heard of this because most of the continental US falls within one zone.

 

If you really _need_ a corroborating source to show that I'm not a raving loony, check the web sites of any of the good compass manufacturers, such as Silva or Brunton.

 

Scott

[Guest mcb]

I agree ScottJ, I now understand I thought that people were saying that you had to have a needle that was different magnetically. I read on a couple compass manufacture's website that the needles were balance for different or multiple zones. The needles are all the same magnetically, they are just different in how they are balance on the bearing to compensate for the pull of the magnetic field of the earth. This makes sense.

 

mcb

[Guest Choberiba]

If you order the Geocaching.com compass to be shipped to a different zone, would it be so tilted as to be useless?

[Guest Geoffrey]

Would be interesting to try the Etrex Vista in different zones. I would like to see if anybody ever calibrated the Etrex Vista in one place on the Earth, then tried it in another???. You would have to re-calibrate the electronic compass in different parts of the world.

 

There are magnetic hot spots around in different places on this planet. This planet has a bit of Iron ore in it. Magnetism is never stable for very long. Over long periods of time the magnetic fields of this Earth change a bit. The magnetic fields on the Sun reverse every 11 years. Compasses have helped travelers for hundreds of years, but they still crap-out in the magnetic hot spots.

 

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My GPS Information Page:

http://members.aol.com/geoffr524/myhomepage/howto.html

This page has many links about GPS information for the beginner.

[Guest Gustaf]

quote:

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If you can get near the equator you can try it - I did in Kenya. I took a large basin with me and 6 gallons of water - the equator is clearly marked btw.

 

Stood about 20 yards north and watched the water swirl out in the conventional way, although it did only slowly start to swirl.

---

 

I have been discussing this with a few teachers at my university (the should now).

 

Summary:

It is not proven that the rotation of the earth could affect the rotation of the swirl. To test this, you need a perfectly shaped basin, filled with water that isn't moving at all (that's the hard part). Then let the water out 1000 times. Do this both north of the equator and south of it. For example, first here in Sweden and then in South Africa. It is possible that you will get a few more left-swirls in the north and a few more right-swirls in the south. But this has been tested and noone has yet had any success (as far as I know).

 

Anywhere close to the equator you would get about 50% of each.

 

[This message has been edited by Gustaf (edited 24 November 2001).]

[Guest Hamster]

Cape Cod: Your boat probably has one of those spheres filled with liquid where the compas can kind of rotate all over the place. However, on a handheld orienteering compass, you have to hold it level so the little needle thingy can rotate freely. If you hold it slanted, the needle will scrape the bottom. Because we are in the 3-d world, the lines of magnetic flux (see previous post about this) do not all point in the same direction, therefore depending on where you are the forces pulling vertically on the needle are different. So, in south america, when you hold the compass level, the needle may be in fact scraping against the bottom of the compass and therefore not pointing in the correct direction. For this reason they are balanced by region. In a boat compass where there is no risk of scraping against the bottom, its not an issue.

[Guest Hamster]

Cape Cod: One more thing. North is not always north and south is not always south. In fact, several times (about 170) in the histroy of the planet the magnetic poles have undergone a magnetic reversal.

 

http://geography.miningco.com/library/weekly/aa032299.htm

[Guest Geoffrey]

I did the toilet trick as mentioned in this thread, and found that the water spun counter-clockwise even though I spun it clockwise with a stick before flushing.

Maybe they are built different in the southern hemisphere.

 

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My GPS Information Page:

http://members.aol.com/geoffr524/myhomepage/howto.html

This page has many links about GPS information for the beginner.

 

[This message has been edited by Geoffrey (edited 24 November 2001).]

[Guest CharlieP]

This is an interesting thread, although I knew about magnetic dip, I had never considered how it affected compass design and calibration. My knowledge of dip came from flying, pilots are taught that a gimballed compass is often inaccurate in a turn, because the needle may be deflected toward the center of the earth as the compass is tilted by the forces in the turn. You can see the compass rotate as the plane enters and exits the turn. But I have a question for the techno-historians, how did the compasses on old sailing ships, like the clippers which rounded Cape Horn, compensate for this? Did they have adjustable weights on the compass? Sets of compass needles or cards calibrated for different latitudes?

 

CharlieP

[Guest Morseman]

quote:

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Originally posted by Cape Cod Cache:

The Earth is a big magnet, north is north and south is south PERIOD. Re-read your basic Earth science book. If a different compass were needed for the north and south hemispheres, then a compass would be useless at the equator.

---

 

True, up to a point.

 

Magnetic north is not at true north, nor necessarily is it at grid north, and it is 'off' by a different amount depending on where you are and what year it is!

 

In fact, magnetic north moves about and acording to a 1999 UK Ordnance Survey map, which was quickly to hand, it was moving at about 12 minutes (3.5 mils) eastwards per year in the UK.

 

There is a theory that says that the Earths magnetic north and south poles will swap over one day. In fact, the Suns magnetic poles swap over quite regularly, every 11 years or so in fact.

 

 

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Morseman

[Guest Jake.Hazelip]

Coriolis effect:

http://www.sciam.com/askexpert/physics/physics20.html

 

Compass differences related to hemispheric locality:

http://www.google.com/search?hl=en&lr=lang_en&q=compass+hemisphere

 

Never, ever fall for junk science. Junk science is things like centrifical force keeping water in a swigning bucket. It's not centrifical force, it's inertia. Anyway, don't ever take what I say to be true, look it up. But, be sure to carefully consider where you look it up. Most junior high and high school science text books are rife with junk science.

 

School text books full of mistakes:

http://www.usatoday.org/news/ndssun04.htm

http://www.psrc-online.org/curriculum/book.html

[Guest Betty]

quote:

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Can anyone recommend a good beginners book or better yet web sight.

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For an excellent tutorial re. using the compass, check out: http://www.learn-orienteering.org/old/