©2005 orienteering cincinnati, inc. the compass what is a compass? com·pass (kŭm’pes, kom-) n....

The Compass©2005 Orienteering Cincinnati, Inc.

What is a compass?

com·pass (kŭm’pes, kom-)

n. 1. A device used to determine geographic direction, usually

consisting of a magnetic needle or needles horizontally mounted or suspended and free to pivot until aligned with the earth's magnetic field.

2. A V-shaped device for describing circles or circular arcs and for taking measurements, consisting of a pair of rigid, end-hinged legs, one of which is equipped with a pen, pencil, or other marker and the other with a sharp point providing a pivot about which the drawing leg is turned.

3. An enclosing line or boundary; a circumference.


• Before the compass, people were traveling about without the fear of getting lost. This was possible because nature offers many direction finders.

• Flowers are one of the best indicators of direction. They will face the sun, even when it is dark with overcast. For all of time, they have been tracking the sun, and they remember where it is.

• Trees will indicate direction by the way they grow. Every area has something unique about it that locals use for navigation.

• The stars give us north on any clear evening.

Before the compass

• Prior to the introduction of the compass, sailors relied solely on the sun for navigation, a task that often caused extensive delays in overcast weather.


origins of the compass

• The first compass was invented in China 2000 years ago.

• A board game where one of the game pieces was a spoon was developed. The spoon would spin around until the handle was pointing north.

• It didn't matter if it was night or day or where the board was placed; the spoon handle always pointed north.

• What did matter was what kind of metal the spoon was made out of. The spoon was made from "tzu shih," or "loving stone," which we know as lodestone.

• Lodestone is a magnetic iron ore found in nature. The spoon was able to spin because of its rounded bottom and long handle.

Chinese Navigators

•The first liquid compass was also invented by the Chinese. •A magnetized piece of iron shaped like a fish was floated in a bowl of water.•Compass makers then replaced the fish with a floating needle, which showed the direction more clearly.


origins of the compass• By the third century AD, the Chinese had discovered much

about magnetism.

• They knew that iron ore, now called magnetite, tended to align itself in a North/South position.

• The magnet was then placed on a piece of reed and floated in a bowl of water marked with directional bearings. These first navigational compasses were widely used on Chinese ships by the eleventh century AD.

Lodestone

Chinese Compass

Chinese Navigators


origins of the compass

• The compass had come a long way from a lodestone spoon, but there was still one problem: Lodestone was needed to magnetize the steel needles.

• It was discovered in 1000 A.D., when steel was being poured into a mold, that if the mold was aligned in a north-south direction and the steel was cooled off immediately, it would become permanently magnetized.

• It would become a magnet. This happens because the steel is poured in line with the earth's magnetic field and is cooled quickly. Lodestone was no longer needed.

• In over a thousand years, the liquid compass has changed very little and is still used today.

Chinese Navigators


Developments of the compass

• The first recorded instance of the compass being used in Europe occurred around 1190.

• This was similar to the early Chinese lodestone model.

• The English had mounted a needle on a pin by the end of the 13th century. This was the basis of the compass as understood today.

• By the 17th century, the needle was changed to become a parallelogram shape, which was easier to mount upon the pin. In 1745 an improvement was made so that the needle would retain its magnetization for longer periods of time.


• The Military picked up the use of the compass for artillery direction and field navigation

Surveyor use of the compass

• Our founding fathers used compasses to survey and explore the wilderness.

• Lewis and Clark used a more primitive compass than this one

Early lensatic


How a compass works

No matter where you stand on Earth, you can hold a compass in your hand and it will point toward the magnetic North Pole. What an unbelievably neat and amazing thing!

Imagine that you are in the middle of the ocean, and you

are looking all around you in every direction and all you can see is water, and it is overcast so you can’t see the sun... How in the world would you know which way to go unless you had a compass to tell you which way is "up"?

Long before GPS satellites and other high-tech

navigational aids, the compass gave humans an easy and inexpensive way to orient themselves.

But what makes a compass work the way it does?


How a compass works

• A compass is a fairly simple device. • It consists of a small, lightweight magnet balanced on

a nearly frictionless pivot point. • The magnet is called a needle. One end of the needle

is often marked "N," for north, or colored in some way to indicate that it points toward north. On the surface, that's all there is to a compass.

• But the underlying reason why a compass works is more interesting.

• It turns out that you can think of the Earth as having a gigantic bar magnet buried inside.

• In order for the north end of the compass to point toward the North Pole, you have to assume that the buried bar magnet has its south end at the North Pole, as shown in the diagram above.

• If you think of the world this way, then you can see that the normal "opposites attract" rule of magnets would cause the north end of the compass needle to point toward the south end of the buried bar magnet.

• So the compass points toward the North Pole.

• But what makes the Earth Magnetic?


core

• The axis of the dipole is offset from the axis of the Earth's rotation by approximately 11 degrees.


• The Earth acts like a great spherical magnet

• It is surrounded by a magnetic field. • The Earth's magnetic field

resembles the field generated by a dipole magnet

• (i.e., a straight magnet with a north and south pole) located at the center of the Earth.

What is the Earth's magnetic field?

The basics


spin


But how is the earth magnetic to begin with?

How the Earth became magnetic

A giant lump of magnetic iron in the centre of the Earth is not responsible for the geomagnetic field.The leading theory is that currents in the fluid outer core, started by the temperature differential between the mantle (crust) and the core, and organized into predominantly helical flows by the spinning Earth, act like a giant dynamo.

Maxwell's equations describe the dynamo effect - that electric currents give rise to magnetic fields, and moving magnets generate electric currents. (In effect, magnetism and electricity are different manifestations of the same phenomenon, usually referred to as "electromagnetism".) The flows in the outer core amplify a small "seed" field captured from the Earth's surroundings as it formed. A positive feedback effect comes into play, with flows of slightly magnetized iron setting up electric currents, which in turn create more magnetism, and so on until the magnetic field becomes strong enough to influence the fluid flows, at which point the magnetic dynamo produces a self-sustaining field.

We're probably most familiar with dynamos in the guise of battery-free bike lights. These contain a magnet and are attached near to the bike wheel. As you pedal, the motion of the wheel turns the magnet, creating an electrical current which is used to power the light.


• No, the magnetic field is different in different places. • In fact, the magnetic field changes with both location and time. • It is so irregular that it must be measured in many places to get a satisfactory picture of its

distribution

Is the magnetic field constant?

• There are several magnetic measurements of interest:• Declination:A sloping or bending downward• Inclination:• Intensity

• Even more mysterious has been the fact that the field has in the past varied in strength and orientation, and has even reversed polarity many times.

• We can tell this from the alignment of small iron particles in layers of rock on the ocean floor and in ancient lava flows.

• A group of scientists in Paris have announced that over the last twenty years, the geomagnetic field has declined in strength by around 10%.

• If this rate continues the field will be completely gone by early next millennium.

• They speculate that we may be in the early stages of a polarity reversal.


declination


Inclination


Intensity


Where is the Pole?

• The North Magnetic Pole is continually moving in an irregular path around its average position because of fluctuations in the magnetic field.


The Pole is moving?

• At the North Magnetic Pole the Earth's magnetic field is directed vertically downward relative to the Earth's surface. Consequently, magnetic dip, or inclination is 90° . In addition, the North Magnetic Pole is the eventual destination for a traveler who follows his or her compass needle from anywhere on Earth.

• The North Magnetic Pole is slowly drifting across the Canadian Arctic. The Geological Survey of Canada keeps track of this motion by periodically carrying out magnetic surveys to redetermine the Pole's location. The most recent survey, completed in May, 2001, determined an updated position for the Pole and established that it is moving approximately northwest at 40 km per year. The observed position for 2001and estimated positions for 2002 to 2005 are given in the table.

• The Earth's magnetic field is shaped approximately like a bar magnet with two magnetic poles.

• One lies in the Canadian arctic, referred to as the North Magnetic Pole, and the other off the coast of Antarctica, south of Australia, referred to as the South Magnetic Pole.


Where is it moving too?

• The figure shows the path of the North Magnetic Pole since its discovery in 1831 to its position in 2001.

• During the last century the Pole has moved a remarkable 1100 km. What is more, since about 1970 the NMP has accelerated and is now moving at more than 40 km per year.


Heading to Siberia

•If the North Magnetic Pole maintains its present speed and direction it will reach Siberia in about 50 years.

•Such an extrapolation is, however, tenuous. It is quite possible that the Pole will veer from its present course, and it is also possible that the pole will slow down sometime in the next half century.


What happens to my compass at the magnetic pole?

• A magnetic compass needle tries to align itself with the magnetic field lines. • However, at (and near) the magnetic poles, the fields of force are vertically

converging on the region (the inclination (I) is near 90 degrees and the horizontal intensity (H) is weak).

• The strength and direction tend to "tilt" the compass needle up or down into the Earth.

• This causes the needle to "point" in the direction where the compass is tilted regardless of the compass direction, rendering the compass useless.


• For a compass to work properly, the compass needle must be free to rotate and align with the magnetic field.

• The difference between compasses designed to work in the northern and southern hemispheres is simply the location of the "balance", a weight placed on the needle to ensure it remains in a horizontal plane and hence free to rotate.

• In the northern hemisphere, the magnetic field dips down into the Earth so the compass needle has a weight on the south end of the needle to keep the needle in the horizontal plane.

• In the southern hemisphere, the weight needs to be on the north end of the needle. If you did not change the weight, the needle would not rotate freely, and hence would not work properly.

What happens to my compass in the southern hemisphere?


• The line of zero declination runs from magnetic north through Lake Superior and across the western panhandle of Florida.

• Along this line, true north is the same as magnetic north.

• If you are working west of the line of zero declination, your compass will give a reading that is east of true north.

• We are working east of the line of zero declination, so our compass readings will be west of true north.

• The exact amount that you need to adjust the declination on your compass to reconcile magnetic north to true north is given in many map legends near the of the map scale.

Magnetic Declination


Magnetic Declination


How do I correct my compass bearing to true bearing?

• You can compute the true bearing from a magnetic bearing by adding the magnetic declination to the magnetic bearing.

• This works so long as you follow the convention of degrees west are negative (i.e. a magnetic declination of 10-degrees west is -10 and bearing of 45-degrees west is -45). Some example case illustrations are provided for an east magnetic declination and a west magnetic declination.


How to make a compass

SUPPLIES YOU NEEDOne clear plastic cupOne pencil or penOne magnetThreadOne needle or small nailOne cork or piece of foam


How to make a compass

• (1) Rub one end of the magnet along a needle. Always rub in the same direction. Do this about 30 times to magnetize the needle. Test it by picking up a pin.

• (2) FLOATING COMPASS. Cut a small piece of cork off and push the magnetized needle through it. Fill the plastic cup with water. Carefully place the cork with magnetized needle into the cup so it is floating in the center.

• (3) CHINESE HANGING COMPASS. Tie one end of a short piece of thread to the center of your magnetized needle. Then attach the other end to a pencil and place it over the rim of the plastic cup.


Types of Compasses

• Gyro Compass

• Digital Electronic Compass

• Mariner’s Compass:

• Handheld or Pocket Compass

• Recreational• Sportsman• Military• Competition

• lensatic compass • wrist/pocket compass • artillery M2 compass • protractor • thumb


Gyro Compass

• Gyrocompasses are used on planes as well as boats and ships.

• At the start of a trip, a gyrocompass is set to the north using a magnetic compass.

• A gyrocompass has a motor inside that readjusts very quickly and keeps them accurate even if the compass is jarred or tipped by turbulence or rough seas.


Digital Electronic Compass

• This is the type of compass that originally would be built into a car.

• They are now available in handheld and wrist models

• These compasses work on a electronic circuit that is influenced by the earth’s magnetic field.

• Digital compasses must be adjusted to allow for distortions in the magnetic field, such as when the car goes over a metal bridge.


Mariner’s Compass

• This is a compass that would be used on board a ship.

• Often a mariner’s compass has the needle attached below the compass card.

• The card is on a pivot so that it can turn freely and always point to the magnetic north.

• The card and needle are covered with a compass bowl and it is filled with a clear liquid.

• This liquid allows the card to float and ‘damps’ it so that it doesn’t swing around with each movement of the ship.


Handheld or Pocket Compass

• This is the type of compass you might take on a hike.

• It has a magnetic needle and a compass card beneath it.

• It can be kept in a pocket or a backpack and can be used to determine the direction in which you are walking.

• Recreational• Sportsman• Military• Competition


Recreational Compasses

• These may be simple devices, used for direction finding or novelties.

• The accuracy may vary wildly.

• The Speed at which the needle settles might not be acceptable in competitive or more serious situations.


Sportsman Compasses

• These are used by hikers, hunters, fisherman…

• Their accuracy is better than a recreational compass.

• The speed and simplicity of use is still slow.


Military Compasses

•Generally the Lensatic compass is used.

•Tritium illuminated for use in total darkness.

•Degree and mil scales.

•Graduated Azimuth (0-360°)

•Edge rule is graduated in meters at 1:50,000.

•Sighting Mirror

•With lanyard, case, with “Alice” belt clip.

•Sturdy aluminum case with metal hinges, painted olive green.

•Waterproof and shockproof.

•Built-in magnifying lens.

•Operating temperature: -50° to +160°F.


Competition Compasses

• Designed for fast and easy reading.

• The classical competition compass with the agronomical grip.

• Easy reading of the map.• Viewable/Detachable scale.• A large and distinct

direction of travel arrow. • Stencil holes for start and

control markings. • Compass housing with

stable needle which settles quickly while running

• fast and extremely stable needle.

• Special magnet in combination with a dampening plate on the needle give optimal orienteering features.

• Wide and straight needle in fluorescent color for easy and fast reading.

Two styles:•Base Plate •Thumb


Parts of a Compass

•Housing: This can be turned from the base of the unit. On the housing will be marked the letters N, S, E and W

•Needle: This always point to the magnetic North Pole.

•Orienting Arrow: This is really part of the housing and turns with the housing. Along with the lines of the base of the compass they enable you to to 'set' a map

•Travel Arrow: If you set a bearing, then once aligned this arrow says which way to go.


Parts of a Compass, More

•Graduated Dial

•Luminous Point

•Base Plate

•Orienting Lines

•Index Line

•Aid Lines

•Magnifier

•Scales: these enable you to take measurements from maps of the distance between two points.


Parts of a Compass, Again

•Mirror

•Bezel or Azimuth Ring: Same as housing


Parts of a Compass, Lensatic

•Cover•Base•Lens


Using a Compass

•NEWS:

Lets get through the fundamentals first. The directions: North, South, East and West. It’s a childhood ditty. (Some people that have struggled with this prefer to remember as NEWS, North, East, West, South.) Take a look at the figure below and make sure we are all on the same page. North is the one we will be dealing with the most, if you are overwhelmed.


Using a Compass

Using the compass alone

•Setting a Bearing: Let's say for example, you want to go northwest. Find northwest on the compass housing. Then turn the compass housing so that northwest on the housing lines up exactly where the large direction of travel-arrow meets the housing.


Using a Compass


•Setting a Bearing: Hold the compass in your hand. You'll have to hold it quite flat, so that the compass needle can turn. Then turn yourself, your hand, and the entire compass, (just make sure the compass housing doesn't turn)Turn it until the compass needle is aligned with the lines inside the compass housing.


Parts of a Compass, Review

•Housing: This can be turned from the base of the unit. On the housing will be marked the letters N,

S, E and W •Needle: This always point to the magnetic North Pole. •Orienting Arrow: This is really part of the housing and turns with the housing. Along with the lines of the base of the compass they enable you to to 'set' a map•Travel Arrow: If you set a bearing, then once aligned this arrow says which way to go.


Using a Compass


•Orienting the Compass: Now, time to be careful!. It is extremely important that the red, north part of the compass needle points at north in the compass housing. If south points at north, you would run off in the exact opposite direction of what you want! And it's a very common mistake. So always take a second look to make sure you’ve done it right!

RED To North


Using a Compass


•Orienting the Compass: A second problem might be local magnetic attractions. If you are carrying something made of iron, it may disturb the arrow. Even a staple in your map could be a problem. Make sure there is nothing of the sort around.

There is the possibility for magnetic sources in the soil, but they are rarely seen.Might occur if you're in a mining district.


Using a Compass


•Orienting the Compass: When you are sure you have got it right, take off in the direction the ‘Direction of Travel Arrow’ is pointing. To avoid getting off the course, make sure to look at the compass quite frequently, say every hundred meters at least. But you shouldn't stare down on the compass. Once you have the direction, aim on some point feature in the distance, and head there.


Using a Compass with a Map

Setting a Map Bearing: Let’s assume that you want to go from the trail-crossing at A, to the rock at B. Put your compass on the map so that the rear edge of the compass is at A. Then, put B somewhere along the forward edge, like it is on the drawing.

Time to be careful again! The edge of the compass, or rather the direction arrow, must point from A to B!

And again, if you do this wrong, you'll walk off in the exact opposite direction of what you want. So take a second look.



Line up North with North: Keep the compass steady on the map. Align the orienting lines and the orienting arrow with the magnetic north lines (also called the meridian lines) of the map. While you have the edge of the compass carefully aligned from A to B, turn the compass housing so that the orienting lines in the compass housing are aligned with the meridian lines on the map. During this process, don't worry about the compass needle!

Be absolutely certain that you are aligning with North on the map, and not the opposite (South). Normally, north will be up on the map.

Keep an eye on the the edge of the compass. If it moves and the edge isn't going along the line from A to B when you have finished turning the compass housing, you will have locked in an error.

Magnetic North(Meridian Lines)



Using the Map Bearing: When you are sure you have the compass housing set correctly, you may take the compass away from the map. Now, you can in fact read the azimuth off the housing, from where the housing meets the direction arrow. Be sure that the housing doesn't turn, before you reach your target B!

Hold the compass in your hand. Hold it quite flat, so that the compass needle can turn. Then turn yourself, your hand, the entire compass, just make sure the compass housing doesn't turn, and turn it until the compass needle is aligned with the lines inside the compass housing. A common mistake is to let the compass needle point towards the south. The red part of the compass needle must point at north in the compass housing, or you'll go in the opposite direction.



Take a Hike:

It's time to take off. But to do that with optimal accuracy, you'll have to do it in a special way as well. Hold the compass in your hand, with the needle well aligned with the orienting arrow. Then aim, as careful as you can, in the direction the ‘Direction of Travel Arrow’ is pointing. Fix your eye on a particular feature in the terrain a reasonable distance in the direction of travel. Then go there. Be careful that as you go, the compass housing doesn't turn.

If you're in a dense forest, you might need to aim several times.



Putting it all together:

Let's review. There are three major steps in using a protractor base compass.

1. Line up the edge of the compass with the line of travel on the map.

2. Rotate the Compass Housing so that the Housing's North Lines are parallel with the Map's North Lines.

3. With the compass against your chest, hold the travel arrow pointing directly away from you. Rotate your entire body until the the compass needle settles inside the confines of the Housing's Orienting Arrow. You are now facing your desired direction of travel.


Using a Compass with a Map, again

Another look at taking a bearing:

Most people can use a compass to tell north from south. Few use it for much else. Yet the ability to take a bearing on a known object, and to use that information as an aid in determining your location, can save many hours of hiking or biking in the wrong direction.

The following technique described here may seem confusing as you read it. Try it, with a map and compass, at an outdoor location where you can follow the steps described. It will soon become second nature




Most Orienteers encounter situations like the following. The map shows a feature. (In this case the church symbol to the right). That's your destination.

You're running down the trail from the north, from the spot we've marked with the letter "Y" (for You). According to the map, two trails will be coming in from the west. You want to turn left at the first of these trails.




Now use your compass to find the bearing to the Church, based on the 360 degrees of a circle. North is 0 degrees, east is 90 degrees, and so on.

First, point the Direction of Travel arrow at the Church. Next turn the dial until the Orienting Arrow (and the letter N) on the dial is aligned with the Magnetic North lines on the map.

Now simply read your bearing at the Index Line. In this case, you find the church to be at a magnetic bearing of 120 degrees.




Rotate the compass dial so that the bearing of your landmark (120) is aligned with the arrow in the center of the rectangular base.

Next, maintain the setting as you remove the compass from the map and rotate the whole compass until the orienting arrow in the center of the dial (the printed arrow)and the swinging magnetic arrow point in the same direction.


Using a Thumb Compass

Doing it the RIGHT way:

Using a thumb compass to orienteer.Directs your attention to the map.Makes compass work a snap.Saves time.Doubles as a thumbing technique.Is always ready.

Let’s get started!



The parallel steering method:Map and compass in the same hand

1. Fold the map to a size you can comfortably handle, preferably so that the magnetic meridians are parallel with the edge of the map.

2. Here you are - there you want to go!Set a direction by putting the 6 JET SPECTRA on the map, in line with the desired direction of travel. From here...to there! Align the map...turn the body...Go!



The parallel steering method:Map and compass in the same hand

3. Orientate the map - turn your body towards the right direction to travel!

Read the position of the needle towards color/symbol and remember which color/symbol the needle is pointing at. For example blue, one dot.

4. GO!The terrain features on the map will be aligned with the terrain on the ground and you have the right course straight ahead.

Read the map and move the compass forward during your run.

Every time you read the map, also check your direction!

Map contact and direction contact - ALWAYS simultaneously!

Constantly maintain contact with your position on the map and your position on the ground.


The Procedure

ONE:

Look at your map.Locate the start triangle.This is your initial position.

Start


The Procedure

TWO:

Turn the map so that the start triangle is nearest you and the first control is away.

Now you and the map are Oriented with respect to each other.

First Route


The Procedure

THREE:

Lay the compass on the map. Point the compass along your planned route.

Now you , the map, and the compass are oriented with respect to each other.

FOUR:

Keeping the map, compass, and yourself all oriented, Rotate your entire body until the Magnetic North Needle is aligned with the Orienting Arrow.

Turn your body around the map

Five:

Go! You, the map, and the compass are all aligned with the first control.


The End

©2005 orienteering cincinnati, inc. the compass what is a compass? com·pass (kŭm’pes, kom-) n....

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