Name: Terry
Status: student
Grade: 9-12
Country: USA
Date: Spring 2012

Question:
What percentage of the sun's total output do we actually receive on Earth?

Replies:
Terry,

First, imagine a sphere around the Sun with a radius equal to the distance of the Sun to the Earth. Using geometry, calculate the total surface area of this sphere (AS = 4 pr r[of our imagined sphere]^2). The portion of this area that the Earth takes up is the area of the cross-section of the Earth (AE = pi r[of Earth]^2). Dividing AE by AS tells us what fraction of the Sun's output (assuming it is equally dispersed to the surface of our hypothetical sphere) reaches the Earth. Multiplying this by 100 gives percent.

Greg (Roberto Gregorius)
Canisius College
Dear Terry,

Very good question. It is probably less that 0.00000001 percent.

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