Final answer:
The four main points on a compass -- North, South, East, and West -- rely on Earth's magnetic field for navigation, with the needle pointing towards the magnetic north. Earth's rotation defines these cardinal directions except at the poles. Compasses have historically been used for navigation and, interestingly, certain animals can also sense magnetic fields to aid their travel.
Step-by-step explanation:
The four main points on a compass are essential for navigation and understanding the Earth's geography. These main points are North, South, East, and West. A magnetic compass uses the Earth's magnetic field to help determine direction, with the compass needle aligning with the Earth's magnetic north and south. The north pole of a compass needle points towards the Earth's magnetic north, which is close to the geographic North Pole. When navigating, directions such as 'West 40° North' indicate an angular direction between two principal compass points.
The Earth's rotation, which goes from west to east, defines these directions, with the exception of the North and South Poles where the directions east and west become ambiguous. This rotational aspect also means that while flying due west along the equator, the compass needle should remain perpendicular to your direction as long as the magnetic and geographic poles coincide. To tell time before pocket watches, people used pocket sundials with embedded magnetic compasses to orient the fin north and use the shadow of the fin to indicate time.
It is interesting to note that many animals, such as pigeons and sea turtles, have the ability to detect magnetic fields, which aids in their navigation.