WORLD'S BIGGEST BLACK-OUT

Auckland Star, Volume LXXI, Issue 297, 14 December 1940, Page 1 (Supplement)

WORLD'S BIGGEST BLACK-OUT

r watch the sky's greatest miracle, the solar eclipse, astronomers and scientists have pursued the elusive moon's shadow to India, Egypt, Chile, Norway, West Africa, even Siberia. So eager was French astronomer Pierre Cesar Jannssen to observe the eclipse of 1871, visible in southern Europe, that he braved the German Army besieging Paris and escaped from the city by balloon. From tropical Caroline Island in the Pacific, a coral atoll with a total native population of seven, the 1883 pelisse was seen. For a closer view of the sun an expedition climl>ed Pike's Peak in Colorado and saw the 1887 spectacle from 14,000 feet above sea level. An eclipse in 1800 lured a partv all the way to Novava Zemlva, icehound island north of Russia and within the Arctic Circle. Wttr Came First War has seldom been allowed to interfere with scientists' observations, but urgent meteorological work for the Navy and R.A.F. this year upset the pirns of British scientists for visiting Cc.lvinia, Cape Colony, on October 1. The earth's biggest natural blackout for 6<> years occurred in a belt 120 miles wide across the parched Karroo which, noted for the transparency of its skies, stretches more than 100,000 square miles across Africa. The Astronomer Royal, genial Dr. Harold Spencer .Tones, who would have headed one of the four British parties which had arranged to view the eclipse, had to rely instead on the reports of Dr. John Jackson. H.M. astronomer at the Cape of Good Hope, whose party was joined by Australian scientists. First recorded eclipse is said to have been that of October 22. 2130 8.C., which was seen from China in the reign of Emperor Chung K'ang. Unfortunately the Court astronomers Ilsi and Ho are recorded to have tieen dead drunk at the time, and they were later beheaded. So well are the heavens and their happening charted to-day that astronomers know that (a) in this century 79 total eclipses of the sun will take

date; (b) a total solar eclipse of th® sun occurs at any one place on earth on an average of only once in every three and a half centuries. Some 93,000,000 miles away blazes the sun, with a diameter of approximately 804,000 miles. Down below is the earth whose diameter is not quite 8000 miles. In between, and roughly 239,000 miles away, is the moon (diameter 21G0 miles). An eclipse of the sun happens when the moon passes between it and the earth. What Happens The moon always trails behind it a great pencil-like cone of black shadow on the side away from the sun. This ■*sone of darkness sweeps through space without touching anything. When it strikes the earth's surface, however, observers in areas where the shadow falls see a total eclipse of the sun. Just before the instant of totality (complete darkness) the blue-black moon shadows, if observed from a height, can be seen flashing across the earth with awe-inspiring velocity, swift as death, silent as doom. Seemingly terrified, birds seek their night quarters. Awakened by the darkness, bats, - owls and other night creatures emerjje stealthily. Sensitive flowers close their petals; the skies run grey or deep purple. Then, out of the weird darkness blazes the greatest glory of an eclipsc - —the sun's corona, a pearly, soft, unearthly light. Radiant streamers stretch millions of miles into space; red tongues of burning hydrogen seem to lick the black circle of the moon. The air becomes curiously cold; dew sometimes forms in fields; stars twinkle. Suddenly, like lightning flash, the sun's light reappears and the earth is awake again. The corona melts into the returning brightness and the black shadow of the moon darts away overland at terrific speed (about 21 miles per second). The eclipse is over. Until as late as 1842 eclipses were still being used to correct the earth's longitudinal measurements. Since then the study of eclipses has contributed largely to the science of solar physics. The sun is an ideal place for studying atoms, because it has terrific heat, extremely small pressures and great electro-ma«netic energy, none of which ha* yet been approached in earthly laboratories im {mcfipflM.

During eclipses astronomers split up the sun's light in spectroscopes and so learn what substances are present in the planet and how they are affected by the tremendous heat and other conditions there. New elements, such as helium, have been discovered in the sun; the height to which various gases rise has been measured. Much has been learned of the nature of these gases, which are also present on earth. Fluctuations in the magnetic current between sun and earth, which affects radio broadcasts, and the barometrical effects of sudden withdrawals of heat from the earth, are also studied. Biggest puzzle to scientists is the corona which accompanies an eclipße. No one knows what it is, although scientists believe it is some sort of electro-magnetic display. That there is some connection between the corona and the famed "sunspots" is maintained by many scientists. US. Expedition Sunspots are immense magnetic whirlpools of incandescent gas with a pronounced effect on the earth's magnetism and its auroras. From earthly observation the spots vary in number and size. The corona's shape varies when the spots are at their maximum and minimum. The only other place where October's eclipse could be observed was in Brazil. To there travelled an American party headed by Dr. Irvine C. Gardner, chief of the Optical Instruments Section of the Bureau of Standards. His eclipse camp was set up at Patos on high plateau land 200 miles from the coast, where totality lasted nearly five minutes. This party's preparations for photographing and charting the eclipse were the most ambitious yet. Its programme included a complete motion picture record in colour, large black and white and coloured photographs of the corona, studies in sky brightness, sky radiation and spectra, temperature and density changes in tha atmosphere during the eclipse. A new feature was the tying together of the different instruments by a combined electric anil vacuum control system which was intended to make the operation of the various units almost automatic. Fw from the. task of operating controls during totality, scientific workers were thus able to observe the eclipse -visually.