What is a compass?

1
What is a compass?

• compass    (kumpes, kom-)n.
• 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.

1. 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.

1. An enclosing line or boundary a circumference.

2
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.

• 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.

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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.

• 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.

Chinese Navigators
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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
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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
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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.

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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 ?

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

Early lensatic ?
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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 cant 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?

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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?

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core

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

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What is the Earth's magnetic field?
The basics

• 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.

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spin
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How the Earth became magnetic

• But how is the earth magnetic to begin with?

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.
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Is the magnetic field constant?

• 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

• 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.

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

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declination
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Inclination
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Intensity
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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.

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The Pole is moving?

• 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.

• 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.

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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.

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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.

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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.

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What happens to my compass in the southern
hemisphere?

• 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.

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Magnetic Declination

• 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.

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Magnetic Declination
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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.

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How to make a compass
SUPPLIES YOU NEED One clear plastic cup One
pencil or pen One magnet Thread One needle or
small nail One cork or piece of foam
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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.

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Types of Compasses

• Gyro Compass
• Digital Electronic Compass
• Mariners Compass
• Handheld or Pocket Compass
• Recreational
• Sportsman
• Military
• Competition
• lensatic compass
• wrist/pocket compass
• artillery M2 compass
• protractor
• thumb

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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.

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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 earths 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.

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Mariners Compass

• This is a compass that would be used on board a
  ship.
• Often a mariners 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 doesnt swing around with each
  movement of the ship.

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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

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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.

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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.

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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 150,000.
• 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 160F.

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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

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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.

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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.

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Parts of a Compass, Again

• Mirror
• Bezel or Azimuth Ring Same as housing

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Parts of a Compass, Lensatic

• Cover
• Base
• Lens

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Using a Compass

• NEWS
• Lets get through the fundamentals first. The
  directions North, South, East and West. Its 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.

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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.

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Using a Compass

• Using the compass alone
• 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.

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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.

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Using a Compass

• Using the compass alone
• 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 youve done it right!

? RED To North
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Using a Compass

• Using the compass alone
• 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.

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Using a Compass

• Using the compass alone
• 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.

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Using a Compass with a Map
Setting a Map Bearing Lets 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.
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Using a Compass with a Map
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)
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Using a Compass with a Map
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.
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Using a Compass with a Map
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.
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Using a Compass with a Map
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.
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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
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Using a Compass with a Map, again
Another look at taking a bearing 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.
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Using a Compass with a Map, again
Another look at taking a bearing 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.
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Using a Compass with a Map, again
Another look at taking a bearing 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.
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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. Lets get started!
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Using a Thumb Compass
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!
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Using a Thumb Compass
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.
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The Procedure
ONE Look at your map. Locate the start
triangle. This is your initial position.
? Start
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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 ?
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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.
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The End