Solar Constant

• The rate at which solar radiation is received outside the earth’s atmosphere on a per unit area basis is called solar constant.
• It is the flux of the solar radiation at the outer boundary of the earth atmosphere on a surface held perpendicular to the sun’s direction at the mean distance between the earth and sun (1.5×1013 cm).
• Every minute the sun radiates approximately 56×1026 calories of energy.
• This energy per unit area called solar constant (S) = total radiation/ total area of spherical shell which is 2langley/min (1390 watt/m^2)
• It fluctuates by 3.5% about its mean value, depending upon the distance of the earth from the sun