The magnetic field was defined as the area surrounding the magnet in which the effects of the magnetic force appear, and the magnetic field lines are imaginary lines that represent the movement of the poles as they appear to be emerging from the north to the south pole outside the magnet, and the opposite happens inside it, and these lines have several characteristics, including that they condense and crowd out the poles And it decreases in other areas, and the reason for this is that the magnetic forces are greatest at the poles, and these lines are also closed. Because there is no single pole in the original, and in this article, we will talk about the magnetic field of the Earth. The Earth's magnetic field is bipolar, that is, it contains two north and south poles on the surface of the earth, and in the ninth century, the German mathematician and astronomer Karl Friedrich Gauss studied the Earth's magnetic field, and he reached that its poles originate inside the earth instead of outside it, and he has also proven that this field Inversely proportional to the square of the Earth’s radius, and this conclusion led scientists to arrive at the origin of the Earth’s magnetic field through several theories, including, despite the fact that the Earth is composed of different minerals, most of which are iron and nickel elements, in addition to containing heavy metals such as Gold, platinum and uranium, most of these minerals have magnetic properties but lose them. Because of the very high temperature<br />present in the Earth's interior, it is not considered a reason for the magnetic field of the earth, but rather it is caused by the effect of dynamo. This occurs when molten minerals flowing in the interior of the earth generate an electric current and since the earth rotates on its axis, this leads to the production of a magnetic field. The lines of the Earth's magnetic field move from the North Pole to the South Pole at each pole, so these lines are almost vertical, and although there is no magnetic strip inside the Earth, it surrounds the entire planet around the planet with a protective area called the magnetosphere as it protects this The planet from harmful cosmic radiation, solar winds, and the magnetic field is responsible for the occurrence of the beautiful aurora phenomenon that can be observed at higher latitudes in the northern and southern hemispheres. The magnetic field of the Earth can be measured in various ways, including the simplest using the compass that is still in use today, which is a device consisting of a permanent magnetized needle balanced with the axis in the horizontal plane, and in the case of a<br />magnetic field, the pointer of this needle deflects towards the magnetic field and thus the angle of inclination can be measured It is also possible to measure the size of the horizontal field, and this occurs by calculating the period of the needle’s oscillation.