What is Extraterrestrial Radiation ?
The sun is a hydrodynamic sphere of intensely hot ionized gaseous matter known as plasma which continuously generates energy by thermo – nuclear fusion reactions. Most of the energy is generated by the fusion of hydrogen to helium. This energy produced in the core is transferred to the surface and subsequently radiated to space.
The sun is a large sphere of hot gases, the heat being generated by various kinds of fusion reactions. The diameter of sun is 1390000 KM and that of earth being 12700 KM. The mean distance between the two is 15000000 KM. Although the sun is very large, it subtends an angle of only 32 minutes at the earth’s surface, this is because the distance between the sun and the earth is very large. The energy incident on the earth outside of its atmosphere is called extraterrestrial radiation. Extraterrestrial solar radiation is ll of the beam radiation type, also known as direct radiation. Hence the beam radiation received from the sun on earth is almost parallel. The radiation coming from the sun is equivalent to that coming from the black surface at 5762 K. This extraterrestrial solar radiation intensity that is nearly constant and is called the solar constant.
The solar constant is the energy from the sun, per unit time, received on a unit surface area, perpendicular to the direction of propagation of the radiation and at the earth’s mean distance from the sun, outside the earths atmosphere. The solar constant has an universally accepted value of 1367 w/(m) x (m). The distance between the earth and the sun varies a little throughout the year. because of this variation, the extra terrestrial flux also varies. The earth is closest to the sun in the summer and farthest in the winter. This variation in distance produces a nearly sinusoidal variation in the intensity of solar radiation I that reaches the earth. This is all about Extraterrestrial Radiation.