Question: what is a radio telescope used for?

Derek McKay-Bukowski answered on 13 Jun 2011:

Normal (optical) telescopes make small, faint, distant objects easier to see. Radio telescopes do the same thing, but for radio waves, rather than light. Let’s imagine you have an FM-radio. It can ‘hear’ the radio station, but only because the radio station is very strong and nearby. The FM-radio cannot tell which way it is to the radio station either. Now, with a radio telescope, you can hear extremely faint signals… not just radio stations, but the natural radio waves given off by the sun, the planets and galaxies – even natural radio waves from our own atmosphere! Additionally, the telescopes can work out exactly where the radio waves are coming from. That makes them very useful for understanding how the universe works (and for detecting things that would otherwise be invisible!)