National Geographic : 1965 Nov
But beginning in 1946, rockets became avail able to carry small telescopes and spectrographs above the atmosphere, and for a few minutes of each rocket's flight the ultraviolet and X-ray emissions of the sun can be studied. Within re cent years balloons have lifted heavy telescopes and cameras above 99 percent of the atmosphere, to an area where the distortion of visible light is largely eliminated (pages 730-31). And now satellites, such as the Orbiting Solar Observatories of the National Aeronautics and Space Administration, provide stable platforms that can point 80 pounds of instruments steadily at the sun, with fine accuracy. Dozens of solar ultraviolet and X-ray pictures can be transmitted to earth daily. Wartime Puzzle Leads to a New Technique Radio astronomy, which is only about a third of a century old, provides another effective tool for studying the higher levels of the solar atmos phere. During World War II, British radar engi neers were puzzled when their instruments tracked intense static signals descending into the western ocean, instead of Nazi bombers coming from the east. They found that such ghost signals rose and fell with the rising and setting of the sun, which was sending out its own radio messages. The sun's radio emanations constantly flicker and pulsate, with frequent violent outbursts. Astronomers tune in on these broadcasts with sensitive antennas. Using huge radar transmit ters, they can bounce beams off the swollen out er atmosphere of the sun and probe its structure and movements. Last year and this, 1964 and 1965, have been designated the International Quiet Sun Years (IQSY). Observers in 43 countries have been keeping a diary of the face of the sun at a time when it is relatively undisturbed by sunspots and solar storms. The IQSY is sequel to the International Geo physical Year (1957-1958), when scientists stud ied the sun and earth under conditions of maxi mum solar activity.* Changes since 1958 have been substantial, since solar activity goes from active to quiet to active again in an average cycle of about 11 years. In these coordinated international surveys, solar telescopes take regular pictures of the sun through various filters; mountaintop observa tories watch the sun's outer atmosphere through coronagraphs; magnetographs make magnetic maps of the sun's face (page 729); radio tele scopes capture the sun's radio signals as wavy *See "The International Geophysical Year," by Hugh L. Dryden, NATIONAL GEOGRAPHIC, February, 1956. 722 The sun takes center stage EACH EVENING when the sun sank into the scorching desert, the Egyptian of 3,000 years ago knew where it went: The sky goddess Nut, her star spangled body arched over the earth in personification of the celestial vault (as shown in the funerary papyrus below), had swallowed the setting orb. During the night it journeyed through her body; each morning she gave birth to the sun anew. In such fashion did ancient man see earth at the center of his universe, dominating the sun. Finally, in the 16th century, the Polish scientist Nicolaus Copernicus liberated astronomy - and outraged public sensibil ities-with his thesis of a sun-centered system. "As if seated upon a royal throne, the Sun rules the family of the planets as they circle round him," wrote Copernicus. That is how Andreas Cellarius, the Dutch geographer, depicted the Copernican system (right), in 1660, with the six then-known planets orbiting the sun. Four representations of earth advanced a slowly dawning concept: As daylight bathes half a planet, the other side sleeps in the night.