All right-- no laughing!!!--- I was just asked this question by some friends to settle a wager -- after giving the question some thought and asking several others the same question w/o a positive answer and realizing that I was not very sure myself -- I ask the experts of this forum " When in Africa -- which way will a magnetic compass point?"-------somtimes I question my worldly knowledge on such matters.

North of course!

Cheers,
Canuck

At first I chuckled at the absurdity of the question, but then had to scratch my head and admit that I didn't quite know for sure!
However, the broader question is really how the compass behaves in the Northern versus Southern hemispheres. North of the equator I would answer confidently that the compass would point to magnetic North, just as it does everywhere else.
South of the equator I would guess that it would still point to magnetic North given that the polarity of the earth's magnetic field hasn't changed, but the doubt occurs as I ponder the effect of the closer proximity of the South pole potentially pulling the magnetic needle southward.
My money is on no difference... Mag North in every case. What do you and your friends say?

All teasing aside, a compass made for the northern hemisphere will try to point north when in the southern hemisphere but it will not work properly.

The needle in a compass has a weight to balance it horizontally. A 'northern hemisphere compass' in the southern hemisphere will not be balanced properly, so it will drag on the housing.

Cheers,
Canuck

Good question, I've been to Australia several times, South America, and Africa, but I guess I never used a compass. If you're in a place like South Africa or South Australia or Tierra Del Fuego, since the earth is round, magnetic north is essentially straight down through the bottom of your feet.

To confim what Canuck mentioned: Magnetic dip

There is always a difference between magnetic north and true north. How much is dependent on longitude. The correction is always marked on a decent map.

A good compass allows you to correct for the difference between magnetic and true north.

You can read about this in any good mountaineering book.

Brett

You guys are killing me. Of course it points north..even in the Southern Hemisphere. At least it did in my airplane.

Magnetic and true north are another issue alltogether. Here's a good way to remember when to add or subtract variation. "True Virgins make dull companions, add whiskey." So you add west and subtract east. jorge

I always wear a wrist compass in the field.
Mine worked just fine in Zimbabwe.

Hunting, compass dip, true virgins,whiskey and it’s not yet April 1. It’s a potent mixture. Hard to know where to start so I’ll just say.

I’ve never had any problems using compasses made in the northern hemisphere and can confirm they all work normally here in Australia i.e. they all point to the magnetic north which is of course at the bottom of the world.
Having said that however I must admit to having been 'bushed on' the odd occasion while out hunting (i.e. not too sure where I was but definitely not lost).
It struck me reading earlier posts that ‘compass dip’ was a concept to be embraced. What better way could one find of deflecting the ridicule that inevitably follows those embarrassing after dark returns to the campfire.
Unfortunately it seems one would have to be hunting from an aircraft for any discernable ‘compass dip’ effect to be evident: http://en.wikipedia.org/wiki/Aircraft_compass_turns

So if you’re using a compass and a map to navigate it doesn’t matter which side of the equator you’re on. Just make sure you adjust for the magnetic declination data printed on your map. If your compass is a good one you’ll be fine.

Since the Southern Hemisphere is closer to the Magnetic South Pole, won't the compass's "S" be more strongly attracted to the South Magnetic Pole than the "N" end is to the North Magnetic Pole? Also, the true South Magnetic Pole wanders about its dipole more than the North Magnetic pole does. Does this make compass deviation/declination in the Southern Hemisphere change on a decade by decade basis?

Magnetic compasses always point to the magnetic north pole, which is not colocated with the geographic north pole. The angular difference between magnetic and true north varies according to your location on the planet's surface. This angular difference is called variation. With the proper chart you can correct the offset to read a true course on a magnetic compass.

Variaton is expressed as easterly or westerly in degrees. This stuff is so basic, and the advent of various electronic devices that I've used over the years, has clouded the specifics for me, but you might post this question on the Aviation Forum . I'm certain that some of the Alaskan bush pilots we have posting there can specifically answer your question.The variation changes and is updated in navigation pubs yearly, or perhaps more often..

Compass deviation is the compass error induced by adjacent magnetic fields, such as the steel hull of a vessel and fields generated by non-shielded electronic equipment such as electric motors and radio sets.

Can one skirt the issue with a hand-held GPS?

jetdvr
I thought it was called declination.

In south central Montana it is 17 degrees.

Slightly west of center Texas it is 8.5 degrees.

This is from some maps I have had for a while.

Tony,

To us earthbound beings and ground pounders, it is declination. The bird men speak a different language

On most topo maps, there is a declination diagram in the right bottom (?) corner. That will tell you how far off a magnetic north reading is to true north. Most maps are scaled and oriented to true north, which requires the conversion exercise via the declination.

Of course, a GPS solves many issues where batteries are not a problem.

Hey, once we figure out the answer to this question, can someone tell me who is buried in Grant's tomb????

quote:

Originally posted by LRH270:
Can one skirt the issue with a hand-held GPS?

At least it reduces the embarrassment of folks turning a map upside down and in all directions to try and figure out where they are!

You migth look for a compass that should boasts a fixed declination adjustment system--standard throughout the range; that's especially useful when working in areas with large magnetic variation

For a reliable compass that will work properly in both northern and southern hemispheres, you might look for a model with the so called "two-zone system" to achieve precise, accurate readings regardless of location.

Some years ago, most compasses functioned well in only one of five geographic zones. That's because the compasses were balanced differently based on the zone's inclination, i.e., the vertical intensity and direction of the Earth's magnetic field - the two zone system, by contrast, consider only the northern and southenr hemispheres, meaning that a a compass with the mentioned design will still work regardless you are located north or south ...

GPS are great, but a reliable compass should always be carried aswell, at least as a back up

quote:

Originally posted by Canuck: A 'northern hemisphere compass' in the southern hemisphere will not be balanced properly, so it will drag on the housing.

Cheers,
Canuck

Yes, except a hand held can be leveled to suit the needle. The one in my 4*4 Suv works at some alarming angles, the ones in planes work going up and down also.

As a student in all things mental, I assume they always "point" N in the southern Hem. as our maps always relate the variation,("East is least, West is best") to the magnetic North pole.
Perhaps the biggest error/problem is deviation, which is when you hold it too close to your rifle, which gives new meaning to the phrase, " What an attractive gun".

George,

A GPS does not soleve the problem completly. It will give your position true, but it does not act as a compass. If you are moveing it will give your direction of travel which is helpfull.

A GPS sholdn't replace a map and compass, however. The battries can die or you can sometimes get in a position where sat.s cannot be acquired...

Brett

quote:

The needle in a compass has a weight to balance it horizontally. A 'northern hemisphere compass' in the southern hemisphere will not be balanced properly, so it will drag on the housing.

I disagree completely. The needle dragging on the case is simply a function of holding the case level. If the needle is balanced it is balanced in either hemisphere.

Magnetic dip as described in the link that Steve posted does not explain the above. I'm afraid that I don't have a better explaination than Wilkipedia, but the phenomenon of magnetic dip is observable in aircraft turns as the compass leads or lags in certain directions even when there is no drag on the compass card. (in fact it would be impossible to lead the turn if there were friction of any sort!) This phenomenon occurs even in compass cards having a remote electronic sensor when it is not synchronized to a gyroscope for stabilization.

quote:

Since the Southern Hemisphere is closer to the Magnetic South Pole, won't the compass's "S" be more strongly attracted to the South Magnetic Pole than the "N" end is to the North Magnetic Pole?

I think this is the best explaination yet, and wipes away any doubt I had earlier. The magnetic needle is always aligned with the polarity of the earth's magnetic field. To prove the point, think of two bar magnets; the end of one magnet will always be attracted to one particular pole of the other, regardless of the proximity of the other end.

The ironic thing about magnets is that the north pole of a magnet was originally named that because observation showed that one end pointed more or less north. The trouble with this is nobody had yet realized that it was the opposite poles of a magnet that attracted. Therefore it is the south pole of a magnet that points toward magnetic north and magnets are marked wrong for the sake of tradition. I have suggested renaming the north pole to the south pole but without any takers as of yet.
In my line of work my guys are constanting chasing the proper declination since magnetic north has the annoying habit of moving by year and whim. True north also moves because the world doesn't spin straight. Mineral deposits affect declination, for instance iron ore will pick up it's own magnetic field from the earth's flux lines. The whole earth as a magnet thing is further complecated by the fact that the magnetic poles aren't exactly opposite. The line between the poles misses the center of the earth by 500 Kms more or less. They also compare theortical to measured dip angles on every reading to be sure that the direction that they give to me is as accurate as possible for today, and so that in later years there is a way to determine exactly where north was when historical data is looked at. After that there is absolute north and grid north as well as true north. a Gyro points at true north, a magnetic compass points where-ever it wants.

.....and you always have to factor in variation: what someone earlier refered to as magnetic dip; of course, if you are around alternate magnetic sources, then you have deviation........ Dogleg is correct: the north pole of your compass needle is attracted to the magnetic south pole, remember, opposites attract. For all you ever want to know about navigation read "The American Practical Navigator"

quote:

.....and you always have to factor in variation: what someone earlier refered to as magnetic dip;

Not the same thing. Variation/declination is the simple difference between mag and true, "dip" is another phenomenon entirely.

It points left

This is why God invented the GPS.

The whole purpose of maps and compasses are to get from point A to point B.

You do have to have a clue where you are however and after 3/4 of a day of in the land cruiser the best map and compass in the world won't necessarily tell you where you are.

You want to get really lost use a compass in the Artic.

quote:

Originally posted by odie:
This is why God invented the GPS.

The whole purpose of maps and compasses are to get from point A to point B.

You do have to have a clue where you are however and after 3/4 of a day of in the land cruiser the best map and compass in the world won't necessarily tell you where you are.

GPS need to be re-calibrated in the southern hemisphere.

Just ask Walter, he'll tell you.

As he took in a nap in the afternoon, I could not help borrowing his GPS and re-naming all the waypoints - giving those in Dubai names in Zimbabwe, and those in Zimbabwe names in Dubai!

Out in the bush, we asked him how far in what direction the camp was. He looked at his GPS, and started scratching his head!

He saw that the camp was 4000 plus kilometers away.

We then had to tell him to re-calibrate his GPS, as he was south of the Equator now.

Saeed -- I still remember that Walter wanted me to get a permit for my wife in Dar --
No wonder he was lost!

Montea6b: Thats not exactly correct: Declination is the arc of an hour circle between the celestial equator and a point on the celestial sphere, measured northward or southward from the celestial equator through 90 degrees and labled N or S to indicate the direction of measurment; while variation is the angle between the magnetic and geographic meridians at any place, expressed in degrees and minuets east or west to indicate the direction of magnetic north from true north. magnetic dip, on the other hand is the angular distance between the horizontal and the direction of a line of force of the earths magnetic force at any point.

Not that any of the above will change the shape of civilization as we know it.

Bryan, sounds like you know your stuff... I'll defer to you! The term I am most familiar with is variation.

quote:

To us earthbound beings and ground pounders, it is declination. The bird men speak a different language

I am guilty of taking a cue from the above quote. (I'm a "birdman"...)

However, I thought the declination diagram on ground maps was for the purpose of determining what the local mag var was? From your definition I can't ascertain a practical use for declination.

I have never needed a compass, I have a since of direction thats sometimes uncanny. The trackers got lost one time and I led them straight to the truck. Another time I was horseback about 100 miles in the Del Carmen Mountains of Mexico and rode directly to the ranch. Guess its a cowboy thang, to dumb to figure out a compass and always knew where the sun sat. In a big city I am toast.

Declination is expressed in degrees and is the variation between magnetic and true north in the particular map's grid. If declination is East of True North, you subtract the declination to get true North. If declination is West of True North, you add the declination to get true North.

Since magnetic North can vary from time to time, the variance is reflected on the map (it is easier to print new maps with revised declinations thanit is to distribute new compasses).

You can also get slight variations in areas with large iron deposits.

I honestly am not familiar with magnetic dip. Never was trained on that. Just given a lensatic compass and a map and told to find my way home.

Jim Manion,
I don't know if dip is of much use in navigation. We use dip to assess survey quality with accelerometer style electronic compasses. It is just one of many qualifers that are recorded on every reading for the purpose of proving the accuracy of the azimuth reading. Close to the equator the dip is close to zero and magnetic compass accuracy is slightly degraded because of it. Bear in mind that "degraded" may be as little as from a few tenths of a degree to about a whole one + or -.

Interesting story

quote:

Declination is expressed in degrees and is the variation betwoon magnetic and true north in the particular map's grid. If declination is East of True North, you subtract the declination to get true North. If declination is West of True North, you add the declination to get true North.

That's what I thought, and this matches the definition of what "birdmen" call magnetic variation. However, Bryan Chick's definition above differs from this...

Bryan?

I wish that I had never entered this conversation: my comments refer to nautical celestial navigation and are a bit beyond this forum. However, I'll try to muddy the waters a bit more; but bear in mind that I am a better navigator than teacher. Variation and magnetic dip is also sometimes known as Magnetic Declination-this is the east/west angular measurment between the meridians(longitude grid lines on a chart) and magnetic north. Imagine the magnetic field which surrounds the earth and imagine the lines of flux which intersect the earth at different angles from the horizontal as the latitude changes towards the poles from the equator. Declination refers to the angular distance north or south of the CELESTIAL equator and a point on the CELESTIAL sphere measured north to south from the CELESTIAL equator through 90 degrees. Deviation refers to the angular measurement from magnetic north caused by local magnetic influences,i.e. the magnetic field of a ship or close proximity to a large body of ferrous material. Another difference in terms is azimuth; many refer to taking an azimuth when they are taking a bearing. To a navigator an azimuth is the horizontal direction or bearing of a CELESTIAL point from a terrestial point.
Now, I promise to not dwell upon this subject anymore, if, by now, I have not completly confused us all

This is going to be a CELESTIAL Topic.

A Tuscanian teacher of mine (a great man) always repeated this warning: take care in putting a question that seems incredibly intelligent and brilliant, 99% of the times they are NOT absolutely so intelligent and brilliant, they are probably a silly question. He always suggested to put the question that seems to be too simple, near to silly.
It will be, probably the question that many want to do, but that noen ha sthe courage to put, the right one.

I'm sorry the initial questione seemed to me a trap question good for a TV quiz, like the question about the difference in weight of a kilo of lead and a kilo of feathers.

quote:

Originally posted by Atkinson:
I have never needed a compass, I have a since of direction thats sometimes uncanny. The trackers got lost one time and I led them straight to the truck. Another time I was horseback about 100 miles in the Del Carmen Mountains of Mexico and rode directly to the ranch.

Some things never change...................

I wish I was as good as Mr. Atkinson. I regularly get lost in thought.

Bryan-

From your post, I take it that you are referring to navigation on the water. To most of us, a sextant is is some cool looking contraption invented to occupy the minds of sailors during months at sea where there is no female companionship.

What you call charts, we call maps. What you call deviation, we call declination (we reserve the use of the word "deviation" and all ots derivatives to describe sailors). We wear shades of earthly colors, you wear, well, white. We sleep in the mud mud and mire eating C rations or MRE's, whenever. You sleep in beds with sheets laundered daily and "dine" three times a day on freshly prepared food (hot) using silverware, china and napkins.

We use a compass that also works in the dark. Any reference to the stars as a navigation aid is limited to general direction - since the damn things move as the earth rotates, your Army and Marine associates are confused by that movement. We identify fixed points and go.

Now granted, if we are off by a fraction of a degree, we can generally end up where we planned to go. A ship being off by a fraction of a degree in the ocean can end up at the wrong rest and recreation port of call, which greatly interferes with one's social schedule.

But we need to be incredibly accurate with our readings and land navigation. There are times when we are required to call in an artillery barrage close to where we are sitting. Those not accomplished in that fine art generally don't stay around for long.

I suppose a ship needs accuracy as to location as well - the wine cellar would soon run dry without frequent resupply.

I did not mean to digress, and CERTAINLY hope that nothing I have said is viewed as a knock on naval (or is it navel?) personnel. Nothing wrong with a thousand or more guys dressed in white volunteering to be isolated from women for 6 months at a time in an area so cramped that they are literally on top of one another. Ahem. Heck, I even know some guys that have done that. Some of my best friends were in the navy. Really!