ABSTRACT
This chapter focuses on Sun-Earth physics and how Geomagnetic Disturbances (GMDs) appear. The Sun emits energy in the form of electromagnetic radiation. The nuclear reactions determine the processes of energy release and chemical elements formation. The crucial condition for solar activity existence is the Sun's magnetic field, which is similar to large-scale Earth's dipole field. The sunspot's brightness in visible light is 20–30% of the surrounding unperturbed photosphere brightness. The solar cycle change is provoked by the interaction between the Sun's rotation and its magnetic field. The Sun rotates differentially, i.e. the highest rotation speed is observed at the equator and the speed on the poles is about 20% lower. Local magnetic fields in active regions cause intensive movement of large masses of ionized gas particles in the form of prominences. The development of space-borne observation methods allowed people to discover the coronal holes, i.e. area of the Sun's corona lower-density plasma.
