compass

[ipswichbiker]

There is only one way to solve this. Some sort of compass off is needed.

[Womble]

I feel some compass use and map reading lessons coming on! :cheer:

maybe something for the Boil?

[Old Git Ray]

Just make sure you have a compass for the right hemisphere, your needle could be 180deg out if its a north one in the south

I doesen't work like that. The needle points to the magnetic north pole regardless of where you are. If you used one at the true North pole it would point towards central Canada. It is currently 500 odd miles from it.(the North Pole)

One small problem in the southern hemisphere is that a silva compass wants to point through the earth a bit and they have to be used at an angle to work.

Actually there are different southern and northern hemisphere compasses due to differences in declination.In the southern hemisphere the south end of the needle is counterweighted so it can be used when level............

Now that I can understand. When I used my UK bought Silva in the Falklands it pointed into the deck at about 30 degrees below the horizon (but still North). A counterweight on the southern end of the needle would have sorted that. It was the 180 deg error thing that was not right.

EDIT: I Just noticed GlosterBoys in his post......Doh....I'll wake up someday..

[Old Git Ray]

Actually there are different southern and northern hemisphere compasses due to differences in declination.In the southern hemisphere the south end of the needle is counterweighted so it can be used when level.

No that's incorrect. You just account for the declination on your usual compass, you don't have a differnt one and anyone who tells you so doesn't really know what they're talking about, despite what google might say.

These are two different problems. Declination is due to the Magnetic North not being at true North - its currently about 530miles to the west of it looking from the UK. A search for Magnetic North on Google Earth shows where it is.
The counterweight would stop the compass trying to point DIRECTLY to North which, when in the southern hemisphere is through the Earth.

[Mike54]

I still maintain that a different compass is not required.

[backofbeyond]

I'll admit right at the start that I know next to nothing about compasses beyond what I was taught in the Boy Scouts so I'll be throwing myself on the mercy of those of you who do know what you're talking about. If I buy a compass here in the UK, as I understand it it'll point towards magnetic north and there are various means by which I can find real north from that. If I then take it to the southern hemisphere it'll still point to magnetic north, but by the direct route which means the needle may point into the ground. Is all that right?

If I decide to upgrade and buy a new compass from somewhere in the southern hemisphere do I understand that it will actually be similar to my original northern version but with a weight on one end to counteract the point-into-the-ground effect? Why don't they just make them to point to the southern magnetic pole and stick the point north paint on the other end? Wouldn't the Aussies etc prefer to know where south was rather than north?

[ross dean]

Dnn't worry about it ... we are overdue for a pole reversal anyway

[Selous]

Backandbeyond, like so many on here, there are quite a few servicmen / women, I know when I went on Exercise with Fiji, Oz & Kiwi forces, in NZ & Oz.
I had my Army issued Prismatic compass http://www.armynnavy.com/catalog/catalo ... ts_id/2266
& my very own Silva Compass, I had no problems what so ever.

FYI From Wikipedia http://en.wikipedia.org/wiki/Compass
How a magnetic compass works
A compass functions as a pointer to "magnetic north" because the magnetized needle at its heart aligns itself with the lines of the Earth's magnetic field. The magnetic field exerts a torque on the needle, pulling one end or pole of the needle toward the Earth's North magnetic pole, and the other toward the South magnetic pole. The needle is mounted on a low-friction pivot point, in better compasses a jewel bearing, so it can turn easily. When the compass is held level, the needle turns until, after a few seconds to allow oscillations to die out, one end points toward the North magnetic pole.
A magnet or compass needle's "north" pole is defined as the one which is attracted to the North magnetic pole of the Earth, in northern Canada. Since opposite poles attract ("north" to "south") the North magnetic pole of the Earth is actually the south pole of the Earth's magnetic field.[7][8][9] The compass needle's north pole is always marked in some way: with a distinctive color, luminous paint, or an arrowhead.
Instead of a needle, professional compasses usually have bar magnets glued to the underside of a disk pivoted in the center so it can turn, called a "compass card", with the cardinal points and degrees marked on it. Better compasses are "liquid-filled"; the chamber containing the needle or disk is filled with a liquid whose purpose is to damp the oscillations of the needle so it will settle down to point to North more quickly, and also to protect the needle or disk from shock.
In navigation, directions on maps are expressed with reference to geographical or true north, the direction toward the Geographical North Pole, the rotation axis of the Earth. Since the Earth's magnetic poles are near, but are not at the same locations as its geographic poles, a compass does not point to true north. The direction a compass points is called magnetic north, the direction of the North magnetic pole, located in northeastern Canada. Depending on where the compass is located on the surface of the Earth the angle between true north and magnetic north, called magnetic declination can vary widely, increasing the farther one is from the prime meridian of the Earth's magnetic field. The local magnetic declination is given on most maps, to allow the map to be oriented with a compass parallel to true north.
In geographic regions near the magnetic poles, in northeastern Canada and Antarctica, variations in the Earth's magnetic field cause magnetic compasses to have such large errors that they are useless, so other instruments must be used for navigation.

I dont agree with the last bit re Canada

[dash]

The counterweight would stop the compass trying to point DIRECTLY to North which, when in the southern hemisphere is through the Earth.

That doesn't make sense Ray. *Both* ends of the needle have an attraction to the respective pole, not just the 'North' end.


Edit: Although I suppose it may try to align itself parallel to the magnetic axis of the earth, which would be somewhere between 'pointing at the north pole' and 'parallel to the ground'.

[Desert Rat]

Agreed, I found out the hard way. GPS packed up in the middle of Morocco. :sick:

Now carry a compass in my rucksack as a backup. As stated earlier, the metal of the handle bars “upsets” the compass.