Why can a compass indicate the direction?

Compass, also called Sina, is mainly composed of magnetic needles installed on the shaft. Under the action of natural geomagnetic field, the magnetic needle can rotate freely and keep in the tangent direction of magnetic meridian, and the north pole of the magnetic needle points to the geographical north pole, so the direction can be distinguished by this property. It is often used in navigation, geodesy, tourism and military affairs. The invention of the compass with physical direction indication consists of three parts, namely Sina, compass and magnetic needle, all of which belong to the invention of China. According to ancient mine records, it first appeared in the Cishan area during the Warring States Period. In the vast sea, how can sailors tell the direction? According to the compass. A small compass, no matter where you put it, always points south at one end and north at the other. Geological exploration, marching and fighting are inseparable from it. Compass is one of the four great inventions in ancient China. As early as 2000 years ago during the Warring States Period, a compass made of natural magnets was called "Sina". Sina is shaped like a spoon. Put it on a copper plate and point your hand to the south. In the Han dynasty, our people made a kind of "guide fish" with artificial magnets to indicate the direction. Later, a better compass was created than the "guide fish" until it developed into the compass we use today. Why can a compass indicate the direction? The earth where we live is a huge magnet. The earth, a big magnetic block, has two poles like ordinary magnets; One pole is near Hudson Bay in North America, called North Magnetic Pole; The other pole is near Vitoja, Antarctica, and is called the South Pole. We know that if a magnet is close to the compass, it will deflect it. This is because magnets have an important property: like-sex repulsion and opposite-sex attraction. The earth itself is a huge magnet, so the compass on the earth always points to the north pole and the south pole. Why is the earth a big magnet? This problem has been studied for many years, and no satisfactory result has been obtained so far.