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What Percent of suns energy reaches earth?

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January 05, 2014 1:29PM

The Earth's orbit is an ellipse rather than a circle; the percentage of the Sun's radiation that hits the Earth varies VERY slightly from January, when Earth is closest to the Sun, to July, when Earth is farthest away. But let's assume that it is a circle, and see what the math says.

The Earth is about 93,000,000 miles from the Sun. The cross-section of the Earth is approximately circular, with a radius about 3950 miles, so the cross-sectional area of the Earth is about pi * 3950^2, or 49,016,699 square miles.

The area of a sphere with the radius of 1 Astronomical Unit is 93,000,000^2*4*pi or 108,686,539,000,000,000 square miles. (Approximately!) Let's assume that the Sun radiates equally in all directions, which is approximately true based on a couple of solar probes that orbit the Sun in polar orbits. It might be off by some trivial factor, but we don't have enough data to know with precision.

So, 49,016,699 square miles of Earth / 108,686,539,000,000,000 square miles of the orbital shell = .000000045%. So, at a close approximation, "Very little".