Types of compasses include the magnetic compass, the gyro compass, the astrocompass and the GPS compass. A compass is a navigational instrument used to determine direction in relation to the Earth's magnetic poles. The earliest compasses were used in India around 1800 BCE.
The magnetic compass is the most common type. These compasses determine the direction of magnetic north using a small piece of magnetized iron or steel, allowing users to determine the other cardinal directions.
The gyro compass, first developed in the 19th century, is a spinning wheel or ball that uses the rotation of the Earth's axis to determine true north, rather than magnetic north. Gyro compasses are often used in large ships or other situations in which determinations of true north are necessary.
The astrocompass is another device that designates true north rather than magnetic north. Astrocompasses rely on celestial data to determine direction, which makes them useful near the North and South Poles where magnetism can make other compasses unreliable. Astrocompasses require accurate information about time, date, longitude and latitude to function properly.
Modern GPS compasses are increasingly replacing other traditional compass models. These devices make use of satellites to determine the user's location and direction. GPS signals are not always accessible, however, and the military and most ships still make use of older compasses as well.