What causes this difference?|||Earth is absorbing energy in form of short wave radiation (UV light) coming from Sun, but Earth is emitting that radiation back to space in form of long wave radiation (infrared light)!!!!|||Energy striking earth from the sun only lands on half the planet. Energy radiating from the earth to the cold depths of outer space (2.9Kelvin background temperature, -480掳F) occurs around the entire planet all the time.
The difference in the amount of energy is ridiculous since the sun is so huge and hot (2,500掳 surface, much hotter inside) and the earth is relatively cool at about 70掳F average.|||The amount of energy absorbed and re-emitted by Earth is essentially the same - that's why Earth is in thermal equilibrium. Otherwise, the temperature would be continuously rising or falling. If you're a purist you can say that Earth actually emits a little bit more energy than it absorbs from Sun due to the energy produced on Earth surface from chemical and biological processes occuring there, but the amount is so small in comparison that it is negligeable.
The difference in the energy absorbed and emitted by Earth is the wavelength. Sun's peak energy wavelength is around 500 nm (visible light, yellow color) because Sun's effective surface temperature is around 5800 K. Earth emits radiation in far infrared, with peak wavelength of approx. 10 microns, corresponding to an effective surface temperature of 290 K. The difference is because of the difference in surface temperatures of the Sun and Earth.
The wavelength can be calculated with the Wien Displacement Law equation:
位max x T = constant = 2.8978 x 10^-3 mK|||http://yourinfo.daymy.com
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