164 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1951 



for this reason that astronomers trek to distant parts of the globe 

 from solar eclipse to solar eclipse, and from year to year. From time 

 immemorial eclipses have interested men. In ancient times they were 

 greeted by mystic rites, and engendered fear and uncertainty in the 

 people visited by them. 



As with the products of modern science, the results of the ancient 

 science of eclipse prediction gave to its users information of vast 

 political significance. And so it was, according to Prof. S. A. Mit- 

 chell in his book Eclipses of the Sun, that an ancient Chinese imperial 

 edict charged the court astronomers with the responsibility for pre- 

 dicting all solar eclipses. It appears, however, that in approximately 

 2000 B. C. the astronomers Hsi and Ho let their calendars fall into 

 disorder, became dead drunk, and then were caught unawares by 

 the occurrence of a solar eclipse. For this it seems that the un- 

 fortunate royal astronomers were put to death. Modern astronomers, 

 happily, have an easier time. They predict their eclipses with auto- 

 matic calculators, and, furthermore, have devised many types of 

 astronomical instruments with which to observe the eclipse features 

 of the sun by artificial means. 



At a total eclipse, features of the sun that are normally invisible 

 show up spectacularly. By extensive study of these eclipse features, 

 modern astronomers are making great progress in attacking the un- 

 solved problems of the sun. But let me turn first to a discussion 

 of some of the basic facts about the sun. 



The sun interests astronomers particularly because it is the near- 

 est star to earth. It is the only star close enough for them to study 

 in great detail. All other stars in the sky appear as mere pinpoints 

 of light, even in the most powerful telescopes. But on the sun, in- 

 dividual features are readily distinguishable, and we can gain a rela- 

 tively intimate view of what goes on in a rather typical star. 



As far as we on earth are concerned, the sun is distinguished pri- 

 marily by proximity. By comparison with the other stars, it is a 

 rather undistinguished body. It is neither extremely large nor 

 strikingly small. It is midway within our realm of experience as 

 to brightness, color, chemical composition, and many other char- 

 acteristics. Fortunately for us it is also a very stable star, not 

 partaking of the violent excursions that characterize some of the stars 

 we have studied in detail. The sun is a mere 93 million miles away. 

 The nearest other star we know of is more than 200,000 times farther 

 from us. Its proximity makes the sun by far the most important 

 source of energy available to man. This tremendous available reserve 

 of heat, light, and other radiations provides a climate and environ- 

 ment favorable for life as we know it here on the earth. 



