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radiant energy does not require a medium to propagate. Infrared is one form of radiant energy. The energy output of the sun, although including infrared, is mostly at much higher energies that IR represents. Only cold bodies such as the earth emit radiant energy primarily in the infrared.
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Infrared is a tiny part of the eleectromagnetic spectrum we receive form the sun. From Gamm waves, x-rays, visible light all the way otu to radio waves.
But, heat is how we perceive the vibration of atoms in a very narrow band of their activity. Almost like the fact we can only see a small band of the electromagnetic spectrum, visible light, but not radio waves. So we can really only perceive heat between about -75F to a few 100F, anything outside those are lethal. So we could never 'feel' the heat of the sun or a nuetron star.
So, you are correct. But the Teacher was presenting a concept that even scientists dont completely understand, simplified for the entire class and your explanation was beyond what was necessary. So you were wrong too.
Its interesting how different reality is from our perception its very possible that meeting aliens the concept of heat would be very unusual to them.
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"Emitting infrared radiation" is what we mean when we say losing heat by radiation. When you feel cold on a clear night, it's because you are radiating infrared.
Your "rebuttal" is partly correct. Most of the sun's energy is in the visible part of the spectrum, and so it comes to us as VISIBLE electromagnetic radiation, not infrared. That's why those wavelengths are visible in the first place. We're evolved to see the energy that the sun puts out. It is then absorbed by the ground, which heats up, and re-radiates in the infrared.
But how is that a rebuttal anyway? You're both saying the energy reaches earth via electromagnetic radiation. Where are you differing?