The electromagnetic spectrum is the range of frequencies of electromagnetic radiation. There are many different types of radiation including radio frequencies, microwaves, ultraviolet light, x-rays, gamma rays and infrared radiation. Infrared can be broken down into far-infrared, mid-infrared and near-infrared. It is the far-infrared part of the spectrum (from about 300GHz to 30THz) that is most absorbed by water. The water in the Earth's atmosphere absorbs so strongly in fact that the atmosphere becomes opaque.