These are the longest of all the electro-magnetic waves, and are used in telecommunications (radio and TV broadcasts, as well as portable phones and walkie talkies).
Some TV sets have aerials on top:
Some radio waves come through the earth's atmosphere from space. Astronomers look at these waves using giant radio telescopes.
The advantage of radio astronomy is that you can do it during the day, at night, and even when it's cloudy!