Radio telescopes History of the telescope

the 250-foot (76 m) lovell radio telescope @ jodrell bank observatory.

radio astronomy began in 1931 when karl jansky discovered milky way source of radio emission while doing research on terrestrial static direction antenna. building on jansky s work, grote reber built more sophisticated purpose-built radio telescope in 1937, 31.4-foot (9.6 m) dish; using this, discovered various unexplained radio sources in sky. interest in radio astronomy grew after second world war when larger dishes built including: 250-foot (76 m) jodrell bank telescope (1957), 300-foot (91 m) green bank telescope (1962), , 100-metre (330 ft) effelsberg telescope (1971). huge 1,000-foot (300 m) arecibo telescope (1963) large fixed natural depression in ground; central antenna can steered allow telescope study objects twenty degrees zenith. however, not every radio telescope of dish type. example, mills cross telescope (1954) example of array used 2 perpendicular lines of antennae 1,500 feet (460 m) in length survey sky.

high-energy radio waves known microwaves , has been important area of astronomy ever since discovery of cosmic microwave background radiation in 1964. many ground-based radio telescopes can study microwaves. short wavelength microwaves best studied space because water vapor (even @ high altitudes) weakens signal. cosmic background explorer (1989) revolutionized study of microwave background radiation.

because radio telescopes have low resolution, first instruments use interferometry allowing 2 or more separated instruments simultaneously observe same source. long baseline interferometry extended technique on thousands of kilometers , allowed resolutions down few milli-arcseconds.

a telescope large millimeter telescope (active since 2006) observes 0.85 4 mm (850 4,000 µm), bridging between far-infrared/submillimeter telescopes , longer wavelength radio telescopes including microwave band 1 mm (1,000 µm) 1,000 mm (1.0 m) in wavelength.