The closest star to Earth, as we know, is the sun.It emits electromagnetic waves having different lengths.For example, some are presented in the form of light, the other - in the form of infrared rays bringing warmth, and others - is a group of invisible to the human eye rays (radio waves, ultraviolet, X-ray).
short-range radio waves and visible light, it is best to pass through the Earth's atmosphere.Gamma-rays, ultraviolet and X-ray absorbed by the air envelope.At the boundary of the Earth's atmosphere the intensity of solar radiation is constant and amounts to 1.35 kW / m2.
sun is the only source of natural light and heat on the planet.Diffuse and direct radiation - the main types of solar radiation.Rays passing through the existing atmosphere, a small degree of heat.Reaches the surface of the Earth solar radiation is not scattered or absorbed in the air shell, called a straight line.The intensity of radiation depends on the area of ​​geographic latitude: the poles of the Earth's equator flow is reduced, the intensity is reduced, in particular by increasing and reducing the transparency of cloudiness in the atmosphere.
Due to the fact that air containing small dust particles, water droplets, particles of salt crystals separate rays coming from the light encountering these obstacles are scattered.This is called solar radiation scattered.It becomes about 25% of the total flow of the absorbed rays.In a cloudless day the scattered radiation is 0.07 kW / m2, cloudy, overcast skies - 0.5 kW / m2.With the reduction of the height of solstice, increasing clouds, reduced transparency of the atmosphere increases the proportion of the radiation.Studies show that at low latitudes share of the scattered radiation is significantly lower than in the temperate and high latitudes.The surrounding natural light on a cloudy day is fully guaranteed by these beams.
total solar radiation is made up of all the direct and scattered radiation reached the Earth.Its concentration will depend on various factors, including the duration of the day, the transparency of the angle of incidence and cloud in the atmosphere.For example, in tropical latitudes, the annual figures total radiation of the order of 200 kcal / cm2 in the polar zone - about 50 kcal / cm2.
in small volumes solar radiation is absorbed by impurities and molecules of atmospheric gases.At the same time hitting the Earth radiation is absorbed by the planet's surface in part and partly reflected back into the atmosphere.
There is a quantity that characterizes the ratio of reflected light to the incident on the earth's surface - the albedo.This figure is expressed as a percentage.Note that the albedo covers a fairly wide range and depends on the territory.So, for the steppes and forests, this figure is about 13%, and in the fresh snow cover increases to 90%.There substantial dependence of the albedo of the water surface on the angle of incidence.When the direct solar radiation and high altitude of the sun this indicator - about 3-4%, with a low standing - almost 100%.For scattered radiation albedo is about 8-10%.And almost no dependence on the height of solstice.
As is known, light from the sun is the source of life on Earth, which has a direct impact on the human body, the thermal state, metabolism and functional activity of organs and systems, and more.
solstice depends on the height and intensity of ultraviolet radiation reaching the surface.At the height of the sun is less than 25% of UV radiation, the most biologically active earth, however.
