Energy from the Sun

A great quantity of heat reaches the Earth from the Sun, through the layers of the atmosphere. Only a part of solar radiation reaches the Earth’s surface: 34% of solar radiation is reflected into space by the atmosphere, by clouds and by the Earth’s surface itself. Of the remaining 66%, 19% is absorbed by water vapour, by clouds and by the ozone layer and only 47% on average is absorbed by the Earth’s surface. Solar energy reaches the ground largely in the form of ultraviolet rays, that pass through the atmosphere easily and are subsequently absorbed by the ground. On getting heated, the ground releases the energy in the form of infrared radiation which has a longer wavelength but is more calorific. Infrared radiation is in turn absorbed by the atmosphere, that gets heated: in practise, therefore, the atmosphere behaves like the glass of a greenhouse that allows ultraviolet rays to pass but detains the infrared ones.

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