A recent development is the electronic compass, or fibre optic gyrocompass , which detects the magnetic directions without potentially fallible moving parts. This device frequently appears as an optional subsystem built into GPS receivers. However, magnetic compasses remain popular, especially in remote areas, as they are cheap, durable, and require no electrical power supply. Modern compasses usually use a magnetized needle or dial inside a capsule completely filled with fluid oil, kerosene, or alcohol is common.
The fluid dampens the movement of the needle and causes the needle to stabilize quickly rather than oscillate back and forth around magnetic north.
North on the needle or dial, as well as other key points are often marked with phosphorescent , photoluminescent , or self-luminous materials [ 4 ] to enable the compass to be read at night or in poor light. Many modern recreational and military compasses integrate a protractor with the compass, using a separate magnetized needle. In this design the rotating capsule containing the needle has a transparent base containing map orienting lines as well as an orienting 'box' or outline for the needle.
Other features found on some modern compasses are map and romer scales for measuring distances and plotting positions on maps, luminous markings on the face or bezels, various sighting mechanisms mirror, prism, etc. The military forces of a few nations, notably the United States Army, continue to utilize lensatic field compasses with magnetized compass dials or cards instead of needles. A lensatic-card compass permits reading the bearing off the compass card with only a slight downward glance from the sights see photo , but may require a separate protractor for use with a map.
A "deep-well" design is used to allow the compass to be used globally with little or no effect in accuracy caused by a tilting compass dial. The use of air-filled induction compasses has declined over the years, as they may become inoperative or inaccurate in freezing temperatures or humid environments. Some military compasses, like the U. The purpose of the tritium and phosphors is to provide illumination for the compass, via radioluminescent tritium illumination , which does not require the compass to be "recharged" by sunlight or artificial light.
Mariner's compasses can have two or more magnetic needles permanently attached to a compass card. These move freely on a pivot. A lubber line , which can be a marking on the compass bowl or a small fixed needle indicates the ship's heading on the compass card.
Traditionally the card is divided into thirty-two points known as rhumb s , although modern compasses are marked in degrees rather than cardinal points. The glass-covered box or bowl contains a suspended gimbal within a binnacle. This preserves the horizontal position. The compass functions as an indicator to "magnetic north" because the magnetic bar at the heart of the compass aligns itself to one of the lines of the Earth's magnetic field.
Depending on where the compass is situated on the surface of the Earth the variance between geographic north or "true north" will increase the farther one is from the prime meridian of the Earth's magnetic field. It should be noted that the geographic North Pole and the magnetic north pole are not coincident on the surface of the Earth. The Magnetic North Pole drifts in a circle with a radius of approximately km south of geographic north. It takes roughly years for the magnetic pole to complete one cycle of drift across the Arctic Ocean.
That angle is called the magnetic declination! So what good are all the directions printed on the face of the compass?! The needle keeps pointing in the same direction, but it looks like the directions on the compass rose can point in any direction - depending which way you point the compass!!
I'm gonna show ya!! Let's look at our Luluville-Louberg map again. This time, instead of showing the whole compass rose, the map just shows true north N , magnetic north MN and the magnetic declination!
And I've added a green arrow to show where you want to go - from Louberg to Luluville! You place the map on a more or less flat, level surface! You then place the compass on top of the map! The black end of the compass needle points to magnetic north! That's the only thing you know is pointing in the right direction! The N and the MN on the map are just pointing the way they are because of how you happened to place the map!
The same holds true for the directions on the face of the compass! They point the way they do because of how you happened to set the compass down! But don't forget, the needle floats free of the face of the compass. What you do is place the compass on the map so that the 'N' on the face of the compass is parallel to the north arrow 'N' on the map! Any interactives on this page can only be played while you are visiting our website.
You cannot download interactives. Magnetism is the force exerted by magnets when they attract or repel each other. Students learn how the sun's activity and magnetism drive space weather and impact Earth's living and technological systems. Students create and observe ferrofluids to understand magnetic field lines and how they can affect planets. Join our community of educators and receive the latest information on National Geographic's resources for you and your students. Skip to content.
Twitter Facebook Pinterest Google Classroom. Encyclopedic Entry Vocabulary. A compass is a device that indicate s direction.
It is one of the most important instrument s for navigation. Magnetic compasses are the most well known type of compass. While the design and construction of this type of compass has changed significant ly over the centuries, the concept of how it works has remained the same.
Magnetic compasses consist of a magnetized needle that is allowed to rotate so it lines up with the Earth's magnetic field. The ends point to what are known as magnetic north and magnetic south.
Ancient Greeks understood magnetism. As early as 2, years ago, Chinese scientists may have known that rubbing an iron bar such as a needle with a naturally occurring magnet , called a lodestone , would temporarily magnetize the needle so that it would point north and south.
Very early compasses were made of a magnetized needle attached to a piece of wood or cork that floated freely in a dish of water. As the needle would settle, the marked end would point toward magnetic north. As engineer s and scientists learned more about magnetism, the compass needle was mounted and placed in the middle of a card that showed the cardinal direction s—north, south, east, and west. A spearhead and the letter T, which stood for the Latin name of the North Wind, Tramontana , signified north.
This combination evolve d into a fleur-de-lis design, which can still be seen today. All 32 points of direction were eventually added to the compass card. Historians think China may have been the first civilization to develop a magnetic compass that could be used for navigation. Chinese scientists may have developed navigational compasses as early as the 11th or 12th century.
Western Europeans soon followed at the end of the 12th century. In their earliest use, compasses were likely used as backups for when the sun, stars, or other landmark s could not be seen. Eventually, as compasses became more reliable and more explorers understood how to read them, the devices became a critical navigational tool. This discrepancy between magnetic north and true north is called variation by mariner s or pilot s or magnetic declination by land navigators and varies depending on location.
Variation is not significant when using magnetic compasses near the Equator , but closer to the North and South Poles, the difference is much greater and can lead someone many kilometers off-course. Navigators must adjust their compass readings to account for variation. Other adaptation s have been made to magnetic compasses over time, especially for their use in marine navigation.
When ships evolved from being made of wood to being made of iron and steel , the magnetism of the ship affected compass readings. This difference is called deviation.
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