Once this was known, the idea of studying the universe in the radio was born. With Jansky's accidental discovery of a cosmic source of radio waves, our view of the Universe suddenly grew, from the relatively limited visible window into the radio. The antenna absorbs radio waves and transmits them to a signal amplifier. After the signal is amplified it is recorded by either a tape recorder or a computer. Since radio waves are long, the surface of a radio telescope does not need to be extremely smooth in order to focus them.
Radio telescopes are often quite large.
The largest, Arecebo, in Puerto Rico, is a radio observatory built right into a hillside, and is about 300 meters across. Because of its size it can detect long wavelength radio waves. Radio waves are detectable day and night, since the Sun is not a very strong source of radio waves when it is up during the day. Radio waves are longer than raindrops and snowflakes, and many pass right through storm clouds to be detected on earth even during the murkiest days and nights. An early technical difficulty of radio astronomy was resolution.