The largest radio telescope in the world is the Arecibo telescope in Arecibo, Puerto Rico. Though radio telescopes have been used since the 1930s, Arecibo has been instrumental in astronomical discoveries since 1960. Developed and operated by Cornell University, radio telescopes are now very valuable tools in observing objects that we are unable to see with ordinary telescopes.

Using the Arecibo telescope, Gordon Pettengill developed a theory about the rotation of Mercury. In 1964, Pettengill used the radio telescope to theorize that the true rotation of the planet was actually 59 days. It had been previously thought that Mercury’s orbit takes 88 Earth days, but this discovery opened new research on the planet and it was revealed that Mercury rotates three times for every two revolutions around the Sun.

In 1989, the Arecibo telescope picked up an asteroid known as 4769 Castalia. Asteroids had been discovered long before radio telescopes, but this was the first time scientists used technology to create an image of what the asteroid looked like. Thanks to radar imaging, Scott Hudson and Steven Ostro were able to develop a three-dimensional model of the peanut-shaped Castalia.

The first binary pulsar was discovered using radio telescopes in 1974. It wasn’t until 1993 that Hulse and Taylor were awarded the Nobel Prize in physics for their discovery. A binary pulsar is a pulsar that has a white dwarf or neutron star nearby that orbits the pulsar to balance the mass and gravitational direction of the pulsar.

Often called “recycled pulsars,” millisecond pulsars are neutron stars with a very fast rotational period. In 1983, the first millisecond pulsar was discovered by Donald C. Backer, Miller Goss, Michael Davis, Carl Heiles and Shrinivas Kulkarni using radio telescopes. Known as PSR B1937+21, this pulsar spins about 641 times a second, and since this discovery, scientists have found nearly 200 more in the universe.

Most recently, in 2008, Arecibo was used to detect prebiotic molecules in a starburst about 250 million light-years from Earth. Methanimine and hydrogen cyanide were discovered on Apr 220, which lies in the constellation Serpens. The discovery of organic molecules is very important to the ongoing debate of finding life on other planets or in other solar systems.