Problem

Sun.jpg

Compute the solar constant, which is calculated using the intensity formula

.

Use the following information.

Surface temperature of the Sun:

Earth-Sun distance:

Radius of the Earth:

Radius of the Sun:

Temperature of outer space:

Solution

Begin with the Stefan-Boltzmann law for radiation to calculate the thermal power of the Sun

.

We can assume that the Sun is a blackbody, so the emissivity is .

Note that the Stefan-Boltzmann constant is .

This power is reduced by the inverse square law of distance

.

This is close to the actual value .

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