Sun

The Sun is a big ball of plasma composed primarily of hydrogen, helium, and small amounts of other atoms or elements. The gravitational interaction is attractive, so in the center of the Sun the protons are close enough together for the nuclear interaction to occur, even though the protons repel one another due to their charge. The energy balance of the Earth due to the Sun is essentially zero, however there is a small amount of geothermal energy generated by radioactive decay. The amount of electromagnetic radiation from the Sun is primarily in the visible range, and this is absorbed and then converted primarily to thermal energy, which has a lower temperature, around 290 K, that radiates at longer wavelengths. The inner planets are quite different because of their distance from the Sun and different mass, which then determines the amount of incident energy and how much atmosphere is retained.