Anyone who has witnessed a total solar eclipse will tell you what a dramatic and emotional sight it is; one of the greatest dramas of the natural world. Small wonder then that in ancient times, before there was a scientific explanation of the event, it was viewed with wonder, awe and even terror and was even invested with great religious significance. However, eclipses have also allowed science to advance because of the unique laboratory which they provide.

Fig 8.1aIn ancient times eclipses were seen as harbingers of doom, an omen of some coming natural disaster or the death or downfall of a ruler. One myth involved an invisible dragon or other demon that devours the Sun during an eclipse. The Chinese would produce great noise and commotion (drumming, banging on pans, shooting arrows into the sky) to frighten away the dragon and restore daylight.

In India people immersed themselves in water up to their necks; believing this act of worship would help the Sun and Moon defend themselves against the dragon. In Japan, the custom was to cover wells during an eclipse to prevent poison from dropping into them from the darkened sky. As recently as the last century, the Chinese Imperial Navy fired its ceremonial guns during an eclipse to scare off the mythical dragon.

Because the exact date, time and place of solar eclipses can now be accurately determined for thousands of years into the past (and future), they can be used to date historical events. History itself has sometimes been influenced by the drama of an eclipse. The earliest record of a solar eclipse comes from ancient China, believed to be on 22 October 2134 BCE. The ancient Chinese document Shu Ching records that "the Sun and Moon did not meet harmoniously". The story goes that the two royal astronomers, Hsi and Ho, had neglected their duties and failed to predict the event, so the emperor was caught unprepared. Even though the Sun returned, the angry ruler ordered the astronomers beheaded.

Fig 8.2An eclipse in 585 BCE in what is now Turkey ended a five-year war between the ancient kingdoms of Media and Lydia, when the final battle finished abruptly due to a total solar eclipse. The eclipse was perceived as an omen, indicating that the gods wanted the fighting to stop.

Louis, son of the emperor Charlemagne, died (some say of fright) after witnessing the five minutes of totality during the eclipse of 05 May 840. The fighting for his throne ended three years later with the historic Treaty of Verdun which divided Europe into the three major areas we know today as France, Germany and Italy.

The unique conditions of a solar eclipse have enabled many scientific advances to be made. The discovery of the element helium (the second

Fig 8.3

most abundant in the universe after hydrogen) was made possible by a solar eclipse. A spectrum of the Sun's corona obtained during an eclipse in India in 1868 by French astronomer Jules Janssen included a mysterious emission line which could not be associated with any known element. The English astronomer Norman Lockyer had also noticed the line and realised that it was due to an undiscovered element which he called helium after the Greek word for the Sun. Helium was not found on Earth for another 27 years.

Fig 8.4a

Einstein's 1915 theory of General Relativity revolutionised our understanding of the cosmos, so experimental proof of the theory was eagerly sought. Einstein himself pointed out that the theory predicted that the light from a distant star passing close to the Sun would be bent slightly by the mass of the Sun and thus appear to us to have moved its position in the sky. However, this effect could only be observed during a solar eclipse when the star could be seen and its apparent position measured. The British astronomer Sir Arthur Eddington took up the challenge and organised two expeditions to observe the May 1919 eclipse and to make the necessary measurements. The results were sufficiently in agreement with Einstein's prediction to support the theory and the eclipse established Einstein as a world celebrity for the first time.

 After thousands of years the total solar eclipse continues to thrill those people lucky (and organised) enough to see one. Even today, a total solar eclipse still allows astrophysicists to make valuable scientific measurements, particularly when coordinated with measurements from observatories in space.

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