Magnetic Compasses and Navigation Systems
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History
Before magnetic compasses became popular, mariners used the position of the stars for navigation. They used the position of a northern star called Polaris as the reference point. This method of navigation came with its challenge. It was quite difficult for sailors to study the stars on cloudy or foggy days. In the 12th Century, European and Chinese mariners discovered that when a lodestone (the first magnet to be discovered) is floated on a stick in water, it aligns in the north-south direction. In addition, they discovered that when a lodestone touches an iron needle for a long time, the needle also aligns in the north-south direction. Hence, to find any other direction, all one needs to know is which way is north.Mechanism
Magnetic compasses are efficient because the Earth acts as a large bar magnet, lying in the north-south direction. This causes other smaller magnets to lie in the same direction. The magnet’s north pole is not the same as the Earth’s geographic north pole. There exist some discrepancies.Challenges of Magnetic Compasses
There is no doubt that magnetic compasses have made navigation a lot more efficient. However, this method of navigation still comes with its challenges. The magnetic compass is stable at the equator. However, at the earth's magnetic pole, you begin to notice some variations. As the magnet gets closer to the Earth’s magnetic pole, the difference between the magnetic pole and the geographic pole increases. In addition, magnetic fields other than the Earth’s magnetic field can affect the magnetic compass. Magnetic compasses are likely to make errors when affected by an external magnetic field. This is common in aircraft and ships because they are made of metals. To counteract this magnetic hull, the compasses used in modern ships are placed on binnacles, containing magnets and steel pieces. Magnetic compasses are also error-prone when one turns from a particular direction. This is because the compass lags behind the turn.Evolution of Magnetic Compasses
Modern compasses have liquids in their capsules. This makes the magnetic needles more stable. In addition, the needles are made with phosphorescent materials. This makes it possible to read a magnetic compass even in the dark. In modern magnetic compasses, one may also find map scales and magnifiers. The map scales are used to plot maps and measure distances more accurately while the magnifier is used to determine the bearing of distant objects more accurately.
