Re: Infra red
Every mater which have temperature above the absolute zero emmits photons. The energy distribution of thei photons obey the Planck law. Depends on the material type there are emmisivity corrections, which are wavelenght specific.
"Visible" is just a small range of the electromagnetic radiation spectra, human eye retina is sensitive to (400 nM = blue ... 600 nM = red). Radiation beyoud this range is invisible. < 400 nM = ultraviolet, > 600 nM = infrared.
The infrared radiation by itself is divided on three ranges - near IR (600 nM .. 5 uM), Middle IR (5 uM .. 50 uM) and Far IR (50 uM ... 200 uM).
The middle IR (AKA thermal IR) is associated to a emmision of body at Earth temperature, where the maximuum of it's Planck distributin Lmax = 2898/T (Lmax in uM, T in K) is about 10 uM.