THE CORONA OF THE SUN

Press, Volume LXIX, Issue 20997, 27 October 1933, Page 17

THE CORONA OF THE SUN

EXISTENCE OF OXYGEN ASTRONOMICAL PROBLEM SOLVED | ! The discovery by the Harvard j Observatory that the pearly light of S the sun's corona is due to the presence of oxygen, and not, as was previously suspected, of some element unknown on earth, which was announced in a cablegram yesterday, may have resulted either from the use of improved instruments or from the application of advanced theoretical methods of spectroscopic analysis. Dr. D. B. Macleod, of Canterbury College, told a representative of "The Press" yesterday ihat while the discovery was interesting from the point of view of pure science, it would probably not prove to be of great importance, unless improved instruments had been used which could be developed for other purposes. j The corona is the gaseous outer en-j velope which surrounds the sun. It j is extremely faint and cannot be satisfactorily observed spectroscopically except at times of eclipse, when photographs show it to be a huge mass of luminous gas, throwing out arms to a distance from the sun's surface which may exceed 300,000 miles. Since it has been impossible in the past to examine it spectroscopically with any degree of success, its components have never been determined, and it may be that the definite ' discovery of oxygen in it is the re- ; suit of improved instruments, sensi-; tive enough to register in spite of its j faint ness. ■- ] Theoretical Methods, \ On the other hand, Dr. Macleod ex- | plained, it was possible that, the ciis- ; covery might have been made by j theoretical methods. All elements, when made luminous by heat, caused ; definite dark lines to show across the spectrum, the same lines occurring invariably for the same element. Under the experimental conditions obtainable in the laboratory, each element showed only a few lines, but under the conditions of great heat such as occurred in the sun or the stars, the elements produced a larger number of lines. During the early investigations' of the lines of the spectrum, it had been supposed' that the lines which could not be identified by comparison with the lines caused by the terrestrial elements under laboratory conditions must be the lines of elements which did not exist on earth. This, however, was only a working hypothesis designed to explain for the time being the large number of spectral lines which could not be identified, and it is many years now since physicists came to the conclusion that it was unlikely to be correct, since ft was proved that the number of elements capable of continued free existence was strictly limited. As a development of this unsatisfactory state of afTairs, a method had been evolved in the last few years by which it was possible to show, by theoretical considerations alone, which of the extra lines seen in the solar spectrum were related to the lines thrown by the terrestrial elements under laboratory conditions. Thus, in the present case, it might have been proved by this theoretical method Hint such lines as were in the light coming from the sun's corona were related to the lines thrown by oxygen in the laboratory. Even though the position of the lines on the spectrum might ho different, it was possible that a relation between them had been demonstrated. If the discovery had been made by this second method, said Dr. Macleod, it might, be of less importance than if it had been discovered through the use of improved instruments. The first would only show that a method already known had been extended, while the second would suggest an improvement in instruments which might enable further discoveries to be | made.