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Q & A: thermal radiation steady-state

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Most recent answer: 05/27/2017
If an object is orbiting the sun, presumably it is absorbing energy in the form of sunlight. How would I calculate the rate of energy absorption and how does the object loose this energy? Since space is a vacuum it cannot be convection. Can blackbody emissions account for the loss? Otherwise, what keeps it from continually warming?
- Bill (age 40)
Menomonie, WI USA

You guessed it- something orbiting the Sun (e.g. us) loses the energy by blackbody radiation. Of course, real objects aren't quite perfect blackbodies, so they are more efficient at exchanging thermal radiation in some frequency ranges than others. Since the Sun's radiant energy mostly arrives in the visible range and the Earth's radiant energy mostly leaves in the infrared, the amount the Earth has to heat up to keep the outflow equal to the inflow depends on how much different frequencies are reflected and absorbed on the surface and in the atmosphere. That's why the greenhouse effect helps warm the Earth and why increasing it by adding more infrared-absorbing gases to the atmosphere will warm it too much.

Mike W.

(published on 05/27/2017)

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