"Since the development of simple compasses, the Earth's magnetic field has been an important aid for navigation, enabling travelers to find their way in uncharted regions. It became an essential tool in the exploration of the planet and facilitated the great voyages of discovery in the late 15th century that established links between the continents. It is one of the central properties of the Earth and has been studied with purpose-built equipment on land, at sea, and in the past half-century from satellites. The magnetic field extends far into space around the planet, where it interacts with the energetic particles from the Sun and interstellar space that impact on the Earth. It produces sideways forces on the rapidly moving, electrically charged particles and deflects them around the planet. In this way, the magnetic field acts as a protective shield against harmful radiation and enables life to exist on the planet."