Who Made the First Dish Telescope?
The first dish (or radio) telescope was made in 1942 by an American, Grote Reber, of Wheaton, Illinois. He constructed his apparatus after studying the experiments of Karl Guthe Jansky, another American, an engineer with Bell Telephone Laboratories, in 1932. Jansky was assigned the job of identifying sources of static that might interfere with radio telephone service.
Jansky’s antenna was an array of dipoles and reflectors designed to receive short wave radio signals at a frequency of 20.5 MHz (wavelength about 14.6 meters). It was mounted on a turntable that allowed it to rotate in any direction, earning it the name “Jansky’s merry-go-round”. It had a diameter of approximately 100 ft (30 m) and stood 20 ft (6 m) tall.
By rotating the antenna, the direction of the received interfering radio source (static) could be pinpointed. A small shed to the side of the antenna housed an analog pen-and-paper recording system. After recording signals from all directions for several months, Jansky eventually categorized them into three types of static: nearby thunderstorms, distant thunderstorms, and a faint steady hiss of unknown origin. Jansky finally determined that the “faint hiss” repeated on a cycle of 23 hours and 56 minutes.
This period is the length of an astronomical sidereal day, the time it takes any “fixed” object located on the celestial sphere to come back to the same location in the sky. Thus Jansky suspected that the hiss originated outside of the Solar System, and by comparing his observations with optical astronomical maps, Jansky discovered in 1935 that the intensity of radio-waves increases as a highly sensitive aerial is directed progressively nearer to the Milky Way Galaxy. The maximum intensity is reached when the antenna is pointing towards Sagittarius— that is to say, towards the galactic centre.
An amateur radio operator, Grote Reber, was one of the pioneers of what became known as radio astronomy. He built the first parabolic “dish” radio telescope, a 9 metres (30 ft) in diameter) in his back yard in Wheaton, Illinois in 1937. He repeated Jansky’s pioneering work, identifying the Milky Way as the first off-world radio source, and he went on to conduct the first sky survey at very high radio frequencies, discovering other radio sources.
The rapid development of radar during World War II created technology which was applied to radio astronomy after the war, and radio astronomy became a branch of astronomy, with universities and research institutes constructing large radio telescopes.
Radio telescopes are called dish telescopes because of the steerable dish-shaped or parabolic reflector which gathers the radiation and focuses it on to a centrally mounted aerial. The surface of the dish is made of a good electrical conductor and the radio waves are reflected from it. The parabaloid shape ensures that all the reflected rays arrive at the central point, where they are “swallowed” by an electromagnetic horn and fed into a receiver.
Since the Second World War the development of radio telescopes has gone ahead rapidly. A 250-foot diameter instrument was installed at the Nuffield Radio Astronomy Laboratories at Jodrell Bank, Cheshire, England. It is under the direction of Professor Sir Bernard Lovell and has already contributed a great deal of new information to astronomy.