THE FUTURE OF THE SUN

New Zealand Mail, Issue 1747, 30 August 1905, Page 65

THE FUTURE OF THE SUN

Modem astronomy has taught us that the sun is the central portion of * great nebula which has been shrink- ' ing lor many hundreds of millions of years. The shrinkage is due to the force of gravitation, the centre of the sun being the centre of gravity of the original nebula and of the present solar system. The sun, of course, is not burning as, a fire bums—that is to say, no oxidation is occurring within him, his temperature being indeed much too high to permit of the occurrence of any chemical combination. As far as we know, the sun’s heat, to which all life on earth is due, is derived solely from the energy released in virtue of his gravitation shrinkage. A diminution of the sun’s diameter of about ,16 inches per annum would account tor all the energy emitted by him. At present we are without evidence that radium i 6 present in the sun, though the occurrence in his atmosphere of helium, which is known to be derived from raoium in terrestrial Laboratories, makes it appear not improbable, despite the lack of any evidence from the spectroscope, that there may he radium in the sun. However, as far as we at present know, it is the force of gravitation that supplies the. sun with his power, and therefore the earth with its life.-' The energy utilised m your reading of this article is, in the long run, GRAVITATIONAL. ENERGY. N ow if there be any cosmic force tbat is uniform and constant in its action, it is gravitation; and if there be any source of power that is commonly thought of as constant and trustworthy, it is the sun. It may be true that he belongs to the category of yellow stars, supposed to he falling ■ n temperature, and destined within an appreciable time to become red hot and finally black; but at any rate nothing calamitous is going to happen in our time—the r, sun may fairly he counted upon. n But it appears that this is only partially true- In the first place there are sun spots, discovered by Galileo nearly three centuries ago. 'though astronomers cannot tell us their nature, yet it is positively known that they cause variations in the electric state of _our atmosphere, and always affect the magnetic needle. JLn so far, then, the sun cannot be regarded as, a constant or invariable source - of energy. Further, we know that there are numerous bright sun spots, besides the dark ones to which the name usually refers; and these also are variable. But quite recently Professor S. P. Langley, one of the foremost of American astronomers, has adduced evidence which points to a striking, if not ominous, conclusion. He is the inventor of an instrument called the bolometer, which is an almost incredibly sensitive thermometer or heat measurer, and is said to be able to indicate the heat radiated from a human face distant one-third of a mile. lNevertheless, the possession of so sensitive an instrument does not suffice to record any possible variation in the heat we receive from the sun until numerous SOURCES OF FALLACY, due to atmospheric variation, are eliminated. This, however, Professor Langley has succeeded in doing, and here are his results. He believes that at the end of March, 1903, contemporaneously with a marked increase in sun spots, something Happened in the sun that caused a rapid fall in the solar radiation, which subsequently has continued to be about 10 pea' cent, less than before! "What the cause of this fall may have been we cannot conjecture; but it is interesting to inquire what consequences it had for the earth. According to Professor Langley such a change in-the sun would reduce the temperature of the earth’s surface by something less than 7.5 deg. Centigrade. Now, when attention is directed to the exact observations made at 89 stations in the north temperate zone, and when -these are compared with the results of many previous years, it is found that a definite fall of more than 2 deg. did actually occur; nor is it possible to conceive “what influence, not solar, could have produced this rapid and simultaneous reduction of temperatures over the whole north temperate zone, and continued operative for so long a period.” Whilst we remain ignorant of the cause of this SOLAR CHANGE we cannot make any predictions as to its persistence or possible accentuation. All we can conclude is that our tenure of this “lukewarm bullet” is perhaps not so certain as some of us have thougm>. But my real purpose in writing this article has been to draw attention to the extreme interest and importance of contemporary work in astronomy. Only the other day I was asked whether astronomy had not practically exhausted itself, little more being left to do than the gaming of greater precision as to the weights and distances of the heavenly bodies. Never was greater delusion. The teleseope, perhaps, has already won

its greatest triumphs; but the spectroscope is only beginning to realise its possibilities. (I need hardly say that the spectroscope was indispensable for Professor Langley’s observations). This instrument has not only toid us that which Comte declared we should never know —the chemical composition of the heavenly bodies —but it is enabling us to write a few scattered chapters of cosmic history. By its means the student is learning to classify the stars, to state whether they are in climax or decline, and to indicate their motion in the line of sight, when the telescope can tell us nothing.

"We may yet expect from the news astronomy a detailed prediction as to the future of the sun; a determination of the question whether or not our stellar universe is finite; an explanation of its arrangement in a plane (the plane of the Milky Way), and of many other great questions. Lastly, let me note a recent observation which hears on the future of the sun and his family. It has been shown that the “proper motion” of the solar system is not at any one of the infinite number of possible angles to the plane of the Galaxy, hut is in that plane. If it should be found, as seems probable, that all the stars move, or are coming to move, m th is plane we must conceive of our Universe as a flat disc bounded by the great circle of the Milky Way. It remains to he wondered whether it is rotating, and whether it is moving as a whole through infinite space.—C. W. Saleeby in the “Academy.”