Stars give out other kinds of radiation besides light. They are all, like light, forms of electromagnetic radiation, which differ in wavelength. They include (from the shortest to the longest wavelengths: gamma rays, X-rays, ultraviolet rays, (light rays), infrared waves and radio waves. Most of these rays are blocked by the Earth's atmosphere, and can be detected only by astronomy satellites in space. But radio waves can pass through the atmosphere and can be studied on the ground. This has led to the science of radio astronomy. It was pioneered in the early 1930s by a Bell Laboratories engineer called Karl Jansky in the USA. It is now one of the most exciting branches of astronomy, which has led to the discovery of intriguing astronomical objects such as quasars and pulsars. Heavenly radio waves are picked up and concentrated by huge dish antennae, known as radio telescopes. There are famous radio telescopes at Jodrell Bank in England and Effelsberg in Germany. They are both fully steerable so that they can be trained to different parts of the sky. But the biggest dish is at Arecibo in Puerto Rico, in the Caribbean. This is located in a hollow on a mountaintop and measures 308 metres across.
