Sunshine, Sunlight intensity, Solar radiation, Source: Wikipedia
Sunshine, Sunlight intensity, Solar radiation, Source: Wikipedia

Solar radiation - Sunshine - Sunlight intensity 

Solar radiation, energy from the sun, in the form of sunlight, supports life on Earth and drives the Earth's climate and weather. Solar radiation is the electromagnetic radiation emitted by the sun. The sunlight intensity and the related energy received is call the solar constant. Depending on the angle of the sun sunlight travels different path lenght described by the Airmass.


The energy radiated by the sun and the average Earth-sun distance of 149.5 million kilometers or 92,960,000 miles lead to 1,367 W/m² of solar energy constantly arriving on the outer surface of the atmosphere - the so called solar constant. The solar constant describes the amount of the incoming perpendicular solar radiation or solar energy in Watt per W/m², measured on the outer surface of Earth's atmosphere.


The sun's rays strike the surface of the earth at different angles ranging from 0º (just above the horizon) to 90º (directly overhead).

The airmass is the optical path length that sun's rays have to travel through Earth's atmosphere. When the sun's rays are vertical the airmass is 1 and the Earth's surface gets all the energy possible.


The more slanted the sun's rays are, the longer they travel through the atmosphere. This coincides with an attenuation by scattering and absorption and a change in radiation spectrum.


Zenith angels of the northern hemisphere with an airmass of 1.5 result in a lesser accessible solar energy of 1000 W/m².