Radio telescopes are useful in astronomy because radio waves can be observed any time of the day or night. Radio waves are also not distorted by the Earth's atmosphere or by gas and dust.
Unlike visible light, radio waves are not absorbed by clouds, so astronomers can make observations even during stormy weather. And while visible light is somewhat distorted by Earth's atmosphere, radio waves are so long that they are not distorted, giving a more accurate picture. In addition, the sun produces a lot of waves in the visible spectrum, but not a lot of radio waves. Because of this, optical telescopes can operate only at night, but radio telescopes can operate day and night.
Most objects in the universe emit radio waves. Some are difficult or impossible to observe in different parts of the light spectrum, because dust and gas absorb and distort so many other wavelengths. Consequently, radio telescopes are the most convenient way astronomers can observe things such as galaxy formation.
As of January 2015, plans are being made to connect a worldwide array of radio telescopes to effectively create a telescope as big as the Earth, called the Event Horizon Telescope. Astronomers hope to use the Event Horizon Telescope to observe the black hole at the center of the Milky Way galaxy. This would not be possible at any other wavelength.