In the Earth's atmosphere, water vapor absorbs many wavelengths of IR energy, while others are not absorbed. Those sections of the Electromagnetic spectrum that it does not absorb, are like windows in the atmosphere, allowing electromagnetic energy to flow freely in and out of the system. Like a window, that allows light to enter and leave. Originally discovered by John Tyndall, most of the infrared coming from the Universe is blocked, absorbed by water vapor (and other greenhouse gases)in the Earth's atmosphere. Those wavelength ranges that can partially reach the surface, are coming through what is called 'water vapor windows'. These windows are how Astronomers can view the Universe with IR telescopes, called Infrared astronomy. These windows also allow orbiting satellites to measure