DK Eyewitness - Astronomy

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The radio telescope radio galaxy This image shows the radio emission from huge invisible clouds of very hot gas beamed out from a black hole in the center of a galaxy called NGC 1316. The maps of the radio clouds, shown in orange, were made by the Very Large Array (p.33). Space telescope Evidence of radio radiation The first evidence of radio radiation coming from outer space was collected by the American scientist Karl Jansky (1905–1950) who, in 1931, using homemade equipment (above), investigated the static affecting short-wavelength radio-telephone communication. He deduced that this static must be coming from the center of our galaxy (pp.62–63). With the discovery of nonvisible light, such as infrared (p.30), and electromagnetic and X-ray radiation, scientists began to wonder if objects in space might emit invisible radiation as well. The first such radiation to be discovered (by accident) was radio waves—the longest wavelengths of the electromagnetic spectrum. To detect radio waves, astronomers constructed huge dishes in order to capture the long waves and “see” detail. Even so, early radio telescopes were never large enough, proportionally, to catch the fine features that optical telescopes could resolve. Today, by electronically combining the output from many radio telescopes, a dish the size of Earth can be synthesized, revealing details many times finer than optical telescopes. Astronomers routinely study all radiation from objects in space, often using detectors high above Earth’s atmosphere (p.7). Gamma rays Optical telescope X-rays Ultraviolet Visible light Infrared telescope Infrared Microwaves Standard broadcast Radio telescope Long radio waves Electromagnetic spectrum The range of frequencies of electromagnetic radiation is known as the electromagnetic spectrum. Very low on the scale are radio waves, rising to infrared (p.30), visible light, ultraviolet, and X-rays, with gamma rays at the highest frequency end of the spectrum. The radiations that pass through Earth’s atmosphere are light and radio waves, though infrared penetrates to the highest mountaintops. The remainder can only be detected by sending instruments into space (pp.34–35). All telescopes— radio, optical, and infrared—“see” different aspects of the sky, caused by the different physical processes going on. Arecibo telescope The mammoth Arecibo radio dish is built in a natural limestone concavity in the jungle south of Arecibo, Puerto Rico. The “dish,” which is a huge web of steel mesh, measures 1,000 ft (305 m) across, providing a 20-acre (8-hectare) collecting surface. Although the dish is fixed, overhead antennae can be moved to different parts of the sky. Amateur astronomer On hearing about Jansky’s discoveries, American amateur astronomer Grote Reber (1911–2002) built a large, movable radio receiver in his backyard in 1936. It had a parabolic surface to collect the radio waves. With this 29-ft (9-m) dish, he began to map the radio emissions coming from the Milky Way. For years Reber was the only radio astronomer in the world. 32
Hot spots Radio astronomers can create temperature maps of planets. This false-color map shows temperatures just below Mercury’s surface. Because Mercury is so close to the Sun, the hottest area is on Mercury’s equator, shown here as red. The blue areas are the coolest. Galaxy Radio waves Focus Bernard lovell The English astronomer Bernard Lovell (b. 1913) was a pioneer of radio astronomy. He developed a research station at Jodrell Bank, England, in 1945 using surplus army radar equipment. He is seen here in the control room of the 250-ft (76-m) diameter Mark 1 radio telescope (later renamed the Lovell Telescope in his honor). The telescope’s giant dish was commissioned in 1957. How a radio telescope works The parabolic dish of a radio telescope can be steered to pick up radio signals. It focuses them to a point from which they are sent to a receiver, a recorder, and then a data room at a control center. Computer equipment then converts intensities of the incoming radio waves into images that are recognizable to our eyes as objects from space (p.57). Parabolic dish High-tech telescope Communications technology allows astronomers to work nearly anywhere in the world. All they need is a computer link. While optical telescopes are sited far from built-up areas (p.27), clear skies are not necessary for radio astronomy. This telescope is the world’s largest, fully steerable, single-dish radio telescope; it is 330 ft (100 m) in diameter and is located near Bonn, Germany. Parabolic dish A very large array Scientists soon realized that radio telescopes could be connected together to form very large receiving surfaces. For example, two dishes 60 miles (100 km) apart can be linked electronically so that their receiving area is the equivalent of a 60-mile- (100-km-) wide dish. One of the largest arrangements of telescopes is the Very Large Array (VLA) set up in the desert near Socorro, New Mexico. Twenty-seven parabolic dishes have been arranged in a huge “Y,” covering more than 17 miles (27 km). Mounting and support 33
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Page 4 and 5: Calculator (19th century) Model of
Page 6 and 7: LONDON, NEW YORK, MELBOURNE, MUNICH
Page 8 and 9: The study of the heavens Watching t
Page 10 and 11: Ancient astronomy Defying the heave
Page 12 and 13: Ordering the universe Star cataloge
Page 14 and 15: The celestial sphere Star trails A
Page 16 and 17: Syene Sun Alexandria Measuring the
Page 18 and 19: Astrology The astrologer In antiqui
Page 20 and 21: The Copernican revolution Nicolaus
Page 22 and 23: Intellectual giants Galileo’s tel
Page 24 and 25: Optical principles Inventor of the
Page 26 and 27: The optical telescope Cameras on te
Page 28 and 29: Observatories The leviathan of pars
Page 30 and 31: Astronomers Fashionable amateurs By
Page 32 and 33: The colors of the rainbow A rainbow
Page 36 and 37: Venturing into space Luna 1 Lunar p
Page 38 and 39: The solar system The solar system i
Page 40 and 41: The Sun The coronagraph In 1930 the
Page 42 and 43: Early moon map The same side of the
Page 44 and 45: Earth earth and the moon The Englis
Page 46 and 47: Mercury Early mercury map Although
Page 48 and 49: Venus People often mistake venus fo
Page 50 and 51: Mars Mars appears pale orange in th
Page 52 and 53: Jupiter This huge, bright planet is
Page 54 and 55: Saturn 17th-Century view In 1675 th
Page 56 and 57: Uranus William herschel (1738-1822)
Page 58 and 59: Urbain le verrier (1811-1877) Le Ve
Page 60 and 61: Travelers in space Not all matter i
Page 62 and 63: The birth and death of stars Catalo
Page 64 and 65: Our galaxy and beyond Edwin hubble
Page 66 and 67: Did you know? Amazing facts The Pio
Page 68 and 69: Cutting-edge astronomy Finding out
Page 70 and 71: Find out more If you want to know m
Page 72 and 73: Glossary Eclipse When one celestial
Page 74: Index A active optics 24, 65 Adams,

DK Eyewitness - Astronomy

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