Question

When the sun is directly overhead, the thermal energy incident on the earth is 1.4 kWm⁻². Assuming that the sun behaves like a perfect blackbody of radius 7 × 10⁵km, which is 1.5 × 10⁸km from the earth show that the total intensity of radiation emitted from the sun is 6.4 × 10⁷ Wm⁻² and hence estimate the sun’s temperature.

Answer 1

The Solar constant S is the heat energy received by 1m² of earth’s surface per second. If R is the radius of the sun and r the earth-sun distance, then the total intensity of radiation emitted from the sun will be σT⁴ Wm⁻² and from the sun’s surface σT⁴.4π R². The radiation received per second per m² of earth’s surface will be