The sun is constantly shining on the earth. That way we have light and heat here. But where does all that energy go? The System Earth gets energy from the sun (or am I making a wrong assumption here?), but how does it get rid of it?
Answer
A (rather small) part of the energy from the Sun that falls on the Earth is reflected back and sent out into the universe. With that light you can see the Earth from the Moon and beyond. Most of the sunlight is absorbed by the atmosphere and especially the Earth itself. That warms the Earth.
An important law of physics says that an object that has heat energy emits radiation. That goes for the Sun, and also for the Earth. It is important that there is a relationship between the temperature of the source and the wavelength (colour) of the radiation. For a body with the temperature of stars – thousands of degrees – the radiation mainly occurs in the visible spectrum; thus we see stars with our eyes that are sensitive to anything between violet and red. For cooler bodies, such as the Earth and ourselves, the radiation is emitted in the infrared, at wavelengths to which our eye is not sensitive.
It is through infrared radiation that the Earth loses the energy it receives from the Sun. And she gets rid of them faster as the infrared radiation can escape more easily. Some gases in our atmosphere (methane, carbon dioxide, water vapour) do not allow infrared radiation to pass through so easily and thus block the heat radiation from the Earth. The energy that these gases absorb in this way ensures that the atmosphere is somewhat warmer than if those gases were not there.
Answered by
Prof. dr. Christopher Waelkens
Astronomy
Old Market 13 3000 Leuven
https://www.kuleuven.be/
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