So Earth receives radiation from the Sun, which heats it up, but then reradiation occurs and Earth loses energy into space. Lets assume the processes are perfectly balanced, this is not about the greenhouse effect. Some of the radiation gets reflected back into space, but much of that radiation stays. What I don't understand is how exactly Earth reradiates energy back into space? We are in space, right? And as far as I know, nothing physical really leaves the orbit of Earth unless humans want it to, which isn't much. Explain please.
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$\begingroup$ I wish there were a way to vote down a question 10 times... at least ... $\endgroup$– Borun ChowdhuryCommented Mar 23, 2018 at 15:31
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$\begingroup$ @BorunChowdhury it's not an unreasonable question if you don't know about blackbody radiation $\endgroup$– Martin BeckettCommented Mar 23, 2018 at 15:36
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1$\begingroup$ "And as far as I know, nothing physical really leaves the orbit of Earth". What does "physical" mean? Does that mean "matter"? Matter (save a few fast molecules in the upper atmosphere, does not leave Earth)--but as per answers, the electromagnetic field is physical (though not matter). It can carry away energy, momentum (c.f., Yarkovsky Effect), angular momentum, and entropy. $\endgroup$– JEBCommented Mar 23, 2018 at 15:46
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$\begingroup$ @borunchowdhury, the quest for knowledge is the asking of many questions. $\endgroup$– niels nielsenCommented Mar 23, 2018 at 17:14
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1$\begingroup$ @niels nielsen Asking many questions to yourself and then selecting the ones you cannot answer and asking others.... $\endgroup$– Borun ChowdhuryCommented Mar 23, 2018 at 17:18
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3 Answers
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What I don't understand is how exactly Earth reradiates energy back into space?
Indirectly. The sunlight coming in warms things up. Warm things give off light. In our case, this blackbody radiation peaks in in the infrared, which is why you don't see it (but pit vipers do).
Escape velocity for Earth, the speed you need to be going to leave us, is about 11 km/sec. Light is moving at 300,000 km/sec. So light has no problem just going on its merry way into space.
answered Mar 23, 2018 at 15:35
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In exactly the same way that the radiation from the sun gets to Earth.
The amount of heat radiation given off by an object depends on its temperature, so as the Earth absorbs energy from the sun it heats up and it radiates some heat into space and cools down.
The temperature of Earth is the result of these two processes balancing. The balance depends on the temperature of the Sun (which controls how much radiation is given off), the distance and size of the Earth (which controls how much of the radiation hits Earth)
answered Mar 23, 2018 at 15:35
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The Earth radiates the Energy because light speed is greater than Earth's escape velocity. However the light since it cannot slow down will lose a really really really tiny amount of energy to the Earth's gravitational field. Some light gets trapped by molecules like carbon dioxide which trap infrared light and that is reradiated to the surface of Earth. However the green house effect on Earth is weak and most of the light just leaves the Earth in the form of radiation.
