The Sun moves the atmosphere, rules the weather and is the energy source for all life on Earth!
The Sun as an energy source
The Sun is the source for life on Earth and has a direct influence on most of the physical processes within the Earth’s atmosphere. Sunlight provides the energy for photosynthesis within plants, which in turn creates the atmospheric oxygen required for us to breathe. The solar daily cycle regulates our lives, and the solar annual cycle determines the seasons and hence the agricultural cycle. Yet the role of the Sun in determining the sate and behavior of the Earth’s climate is much greater than just a simple observation of its warmth would lead us to suppose. The Earth’ atmosphere is literally solar-powered, the Sun being the primary cause of all the atmosphere processes, including the General Circulation, the formation of clouds and the generation of both local and global wind patterns.
The Sun, at the centre of the Solar System, is a typical star 1.392.000 km in diameter, with a mass roughly 1 000 times that of the rest of the Solar System combined. Like most stars it is composed mainly of hydrogen (≈70{154653b9ea5f83bbbf00f55de12e21cba2da5b4b158a426ee0e27ae0c1b44117}), with most of the remainder being helium. The Sun generates its heat and sustains itself from nuclear fusions in the core where the temperature reaches some 15 million °C, and in which an estimated 600 million tones of hydrogen are converted into helium every second. The total solar output into space is 2.33×1025 kJmin-1, but only a tiny fraction (1/2.000.000.000), i.e. one two thousand millionth, of this is actually intercepted by the Earth since the energy received by any planet is inversely proportional to its distance from the Sun. Owing to the eccentricity of the Earth’s orbit around the Sun, the receipt of solar energy on a surface normal to the Sun is 7{154653b9ea5f83bbbf00f55de12e21cba2da5b4b158a426ee0e27ae0c1b44117} more on 3 January at the perihelion (when the Erath is closest to the Sun) than on 4 July at the aphelion when the Earth is furthest from the Sun. The “solar constant” is therefore not a constant. The “solar constant” changes from 1416 W/m2 at the beginning of January to 1321 W/m2 at the beginning of July.