Punker is technically correct, the best kind of correct. However there is a relation between heat and infrared. Actually there is a relation between temperature and wavelength, called "Planck's law", which is a mathematical formula that describes how much light an object emits at any wavelength for any temperature. The sun's surface is at about 5000--6000 degrees, so it's green (when seen without atmosphere, it's white with slightly more green than other wavelengths). Likewise, hot stuff starts glowing red, hotter stuff gets white, even hotter gets blue. And stuff at room temperature glows in the infrared. Extremely cold stuff glows at radio wavelengths (1% of the snow on untuned old television sets was due to the light emitted by the universe itself which is 3 degrees kelvin).
This is simplified (black body and stuff). But yeah, if you want to see stuff on earth without shining a light at it, you've got to be sensitive to infrared because that's what it emits naturally.
This is simplified (black body and stuff). But yeah, if you want to see stuff on earth without shining a light at it, you've got to be sensitive to infrared because that's what it emits naturally.