Facts for Kids

Compass is a small tool that helps you find direction. Most compasses have a tiny, magnetized needle or dial that lines up with the Earth's magnetic field and points toward magnetic north. On a compass, the four main directions are north, east, south, and west. People also use numbers called degrees to measure direction: 0° is north, 90° is east, 180° is south, and 270° is west.

Long ago, people learned to use magnetic tools for divination and later for travel. Today, other devices like gyroscopes, magnetometers, and GPS receivers also help find direction, but the magnetic compass is simple and reliable.

Most modern magnetic compasses have a magnetized needle or a marked dial sitting inside a small clear capsule. Many capsules are filled with a liquid to slow the needle’s wobble, so the direction is easier to read. Common liquids include light oils or alcohols chosen so they do not freeze or burst the capsule.

Compass makers also use tiny glowing paint on the needle so you can read it in low light. Compasses can give wrong answers if a strong magnet, big metal object, or electric device is very near, or if a vehicle speeds up or turns quickly. That is why sailors and pilots sometimes use other tools, like gyrocompasses, for extra steadiness.

Thumb compass — used in orienteering, this small compass clips to your thumb so you can read it while you run. It often has few or no degree marks because you mostly need to point the map the right way and follow a direction quickly.

Some compasses are made for machines or special tasks. An eCompass lives inside phones and watches; it uses tiny sensors and a chip to tell direction. An earth inductor compass uses a spinning coil and Earth’s magnetic field to make an electric signal for direction. Planes sometimes use a vertical-card magnetic compass, which is built to fight a tilt called magnetic dipping.

There are also specialty tools: a Qibla compass points toward Mecca, optical/prismatic compasses help surveyors take very exact bearings, a trough compass was used by old land surveyors, and the luopan is a many-ringed compass used in feng shui. Which of these would you like to try?

Lodestone is a kind of rock that acts like a permanent magnet. People noticed lodestones long ago because they attract pieces of iron. Ancient thinkers such as Thales wrote about these rocks, and the name "magnet" likely comes from a place called Magnesia where lodestones were found.

Many cultures used lodestone for simple direction tools. In China a south-pointing spoon made from lodestone rotated to show north and south. In India, people floated a small iron shape on water to let it turn and point toward one direction. These early ideas helped people see that the Earth itself acts like a giant magnet.

Most magnetic compasses have a needle or a card that can turn freely and rest on a fine pivot. Many use liquid damping — a bit of oil or alcohol that slows the needle so it stops wobbling quickly. This helps you get a steady reading when you are moving or the wind is blowing.

Special designs add useful features. An optical or prismatic compass has a sight and a prism so a surveyor can look at a distant object and read an exact bearing without moving the compass. A trough compass is a long, rectangular box used on old surveying tables. The luopan has many concentric rings with markings for traditional directions. An eCompass uses tiny MEMS sensors and a microprocessor to give digital direction, while an earth inductor generates a small electrical signal by moving a coil through Earth’s magnetic field.

Magnetic north is the direction a compass needle points, but it is not the same as the top of the globe. The magnetic north pole sits far from the true geographic North Pole — almost 1,000 miles away — so a compass does not point to the exact top of the Earth. The difference between true north and magnetic north is called variation (or magnetic declination). Maps usually show the local variation so you can correct your compass reading and find true north.

Local metal and electric currents can also pull a compass needle. This is called deviation and sailors correct it by placing small compensating magnets or by using correction tables made from comparing compass readings to known landmarks. When you use a compass, check the map for variation, keep metal objects away, and, if you are on a boat or a car, be aware that nearby iron can change the reading. How might you test a compass in your backyard?

People learned to make artificial compasses by turning iron into magnets. One easy way is to stroke an iron needle with a lodestone to give it a lasting magnetism. In China, iron-needle compasses were used by the Song period around 1000 AD to help sailors and travelers.

Later, different compass styles spread to Europe and the Islamic world. By about 1300, dry compasses with needles on a pin were common. In the early 1900s, liquid-filled compasses became popular because the liquid steadied the needle and made reading directions easier.