Solar constant
The solar constant is the amount of incoming solar radiation per unit area, measured on the outer surface of Earth's atmosphere, in a plane perpendicular to the rays. It is measured by satellite to be roughly 1367 watts per square metre.
Thus, for the whole Earth, with a cross-section of 125,000,000 km², the power is 170 petawatt.
The angular diameter of Earth seen from the sun is ca. 1/11,000 radian, so the solid angle of Earth seen from the sun is ca. 1/140,000,000 steradian.
Thus, what the sun emits is about 2 billion times the amount caught by Earth.
See also
Earth's energy budget
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