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Feb3-13, 07:06 AM
P: 11,906
Based on Hsun and the surface area of the sun, you can calculate the total power of the sun. In a distance of 1 AU (=the distance earth-sun), this power is distributed over a sphere with a radius of 1 AU, which allows to calculate the intensity.

Simplified: ##H_{earth}R_{earth}^2=H_{sun}r_{sun}^2## where R is the orbital radius of earth and r is the radius of the sun.