Cosmic Background Explorer
High-energy radio waves are known as microwaves and this has been an important area of astronomy ever since the discovery of the cosmic microwave background radiation in 1964. Many ground-based radio telescopes can study microwaves. Short wavelength microwaves are best studied from space because water vapor (even at high altitudes) strongly weakens the signal. The Cosmic Background Explorer (1989) revolutionized the study of the microwave background radiation.