Word: planet
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Dates: during 1980-1989
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...earth by the U.S.'s newest and most versatile earth-observing satellite, a multieyed robot called Landsat 4. Launched last July, it has been faithfully circling the globe, swinging from pole to pole and back again once every 98.9 minutes, taking electronic shots of every spot on the planet, except a small region around the poles. These images are a source of information about crops and forests, oceans, mineral resources and the atmosphere...
Landsat's electronic eyes scan patches of the earth's surface 115 miles square, one after another. (It takes 30,000 images to show the entire planet.) The satellite views each square in different colors, some seven different wave lengths in all, including several "invisible" infra-red frequencies. The images are sent as a stream of radio signals to earth stations, where they are assembled by a computer into full pictures. In many instances, scientists arbitrarily choose the final colors to represent a specific condition; for example, blazing red might indicate healthy crops, while black would mean ailing...
...plus its primary lens, a 22-in. mirror, are tucked inside a thermos bottle-like vessel filled with pressurized liquid helium, which keeps the entire mechanism at 4° above absolute zero (-459.7° F). The detectors are so responsive they could spot a tiny electric bulb on the planet Pluto, nearly 4 billion miles away...
Such sensitivity poses hazards. A fleeting, accidental glance at the sun or the earth could burn out the telescope. Even the strong reflected light of the moon or a bright planet like Jupiter would ruin the observations. For protection, IRAS has a highly polished gold-plated sun shield. But its main insurance is its precise course. Circling the earth once every 103 minutes at an altitude of 560 miles in an orbit that carries it from pole to pole, IRAS roughly follows the line on the earth's surface where day meets night. Along this pathway, the telescope...
...observe young cool stars now hidden behind veils of tiny dust particles that block ordinary light. It will also study old stars near the end of their lives. Such observations could help clarify the mysteries of stellar birth and death. Closer to home, it may spot the long-sought Planet X, which some astronomers suspect is lurking beyond Pluto...