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Sun is the most important source for life on Earth which gives sunlight and heat on Earth. But I was wondering like how does the heat of Sun come on Earth when there is no medium out there in space?

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    $\begingroup$ Same way its light comes...? $\endgroup$ – Mehrdad Jun 14 '15 at 8:41
  • $\begingroup$ By the way, when you sit by a fire, most of the "heat" you get is actually radiation that is absorbed by your body. Unless you're extremely close or on fire, that is. $\endgroup$ – Archimedix Jun 14 '15 at 21:17
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You probably are under the misconception that heat travels only via molecular interactions. (i.e, heat transfer by conduction, which needs a medium of sorts). Heat also transfers by radiation, which the sun is an enormous source of. Electromagnetic radiation does not need a 'medium' to travel through. All types of electromagnetic radiation carry energy, which can be transferred to other bodies when this radiation interacts with them. The continuous stream of photons from the sun is what transfers its 'heat' to us.

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The heat 'comes' as electromagnetic radiation, that is light. Light from the sun is electromagnetic radiation, that is a wave having energy and momentum or a very big amount of quantum particles, photons, that have energy and momentum. The interaction of this electromagnetic interaction is what heats the earth.

Hope this helps.

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The heat from Sun, comes in the form of radiation. To be specific, the infrared part of the EM light is responsible for heating. Infrared frequency is closest to the resonant frequency of most molecules. Thus, when these molecules absorb the infrared radiation i.e. the molecules' electron clouds oscillate at the infrared frequency, there's resonance, which causes the vibration amplitudes to increase appreciably, leading to generation of heat. Note that I assume that you know that Electromagnetic Waves (EM Waves) do not need a medium to travel.

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    $\begingroup$ I agree that infrared light is what is most associated with heat. However it's actually all of the light from the sun that contributes to heating the earth. Some of it is reflected back to space and doesn't contribute. But the rest is eventually absorbed and then re-emitted as lower frequency infrared radiation. $\endgroup$ – cspirou Jun 13 '15 at 21:38
  • $\begingroup$ Yes, the whole of the spectrum comes of course. But, most molecules resonate with infrared radiation. That's why I focused on infrared. $\endgroup$ – Abinash Chakraborty Jun 14 '15 at 5:37
  • $\begingroup$ True, but it is misleading to say that it is mainly IR from the sun causing heat. On the overall EM spectrum of sunlight, IR occupies a very small part. If you calculated the heat contribution from IR there would be a large discrepancy. The earth behaves a bit like a non-ideal blackbody radiator which takes into account all light and emits IR. $\endgroup$ – cspirou Jun 16 '15 at 8:51

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