The Sun is the main source of energy for processes at the Earth's surface and is the driving force behind the weather, climate, life, ocean currents, hydrologic cycle, etc.

Radiation emitted by the Sun and received on Earth:

·        9% ultraviolet radiation (not visible to our eyes; causes tanning, burns and cancer in skin)

·        41% visible radiation (this form of radiation enables us to see the world around us)

·        50% infrared radiation (sensible on the skin as heat; used by reptiles for body temperature regulation)

Approximately one third of all incoming radiation is reflected directly back into space. Infrared and Ultraviolet radiation are absorbed by the Earth and reemitted as infrared radiation. Radiation is lost to space on both the night side and day side of the sphere.

Global Solar Radiation

Global radiation is a measure of all incoming radiation incident on the earths surface. The measurement includes both direct sunlight radiation and diffuse radiation from scattering processes in the earths atmosphere.

Net Solar Radiation

Net radiation is a measure of incoming radiation incident on the earths surface minus the outgoing energy radiated by the earth itself.  Net radiation will usually therefore have a negative value at night.