SUN SPOTS

Evening Star, Issue 16994, 17 March 1919, Page 8

SUN SPOTS

['Ey "J.5.D.,” in Melbourne ‘Argos.’]

The Acting Government Astronomer of Victoria (Dr Baldwin) recently stated that we. were rearing a period of sun-spot maxima, that such periods occurred approximately about every 11 years, that one largo qroup and several isolated groups were visible, and that the largest group was estimated to measure about 90,000 miles by 40,000 miles, the largest spot being about 10,000 miles in diameter. These figures are, compared with measurements of areas on the earth, so enormous as to mystify the average intelligence. They suggest tremendous convulsions on the face and in the body of the sun, and, in view of our intimate relations with that terrible yet benign body, further suggest a wonder as to whether the outbursts have any (and what) effect on the planet we inhabit. That they have some effect on the earth is undoulgted, but the extent of the effect still remains largely a matter of speculation, although earnest endeavors have been made during the past few years, and are still being made, to bring the problem from the domain of speculation into that of exact science. To the average mind the expression "spot” conveys the idea of a small blot, mark, or blemish, on a much larger surface ; but the meaning must always be understood in a comparative sense- So when wo describe a place 10,000 miles in diameter as a spot we must consider, with relation to it, the size of the place on which it appears. According to Mr Ser-vir-s, the United States Astronomer, the diameter of tho sun is approximately 865.000 miles, or more than 100 times the diameter of the earth, whilst the tola! bulk of the sun is over a million limes that of the earth. .Sun spots have been observed of which tho measurements show Dial lire e.irth could be stowed into the cavity evidenced by the spot without touching the sides. One spot liars been observed with a diameter of 30,000 miles; yet compared with tho visible face of the sun this would not bo more than approximately 1 in 50. Take an orange to represent the sun. The largest observed sun spot would not bo larger in comparison than that of ■■ Ihrcepsnnv bit airin-t tho orange. TG- sun is di-'.anl L-m; (he cabb aoprnximai tarn- ■ is imuch moie than ICO limes the sun’s diameter. In other words, 100 bodies ouch the size of tho sun would almost fill tho gap between the sun and the earth. WfIAT ARE SUN SECTS? 13' hat are sun spots, and what causes them? Careful investigation of late years of tho phenomena, aided by spectroscopic research, has thrown a good deal of light on the matter. I thirds' I am well within the lines when I say that the spots are evidence of cavities in the outer envelope of the sun, caused by enormous quantities of matter having been violently r-iect d from an inner part of the sun through the outer envelope. They appear to be'dark; but this again is a matter of comparison! Tho spots .appear dark against the dazzling surface of the sun in the same manner fas Mr Durham explains) as “Me strong electric light appear.-; as a dark pint when placed between ns and the sun.” As giving fame slirht idea of tho enormous forces at work in the sun, iudniK-es have Boon observed whore masses of matter have b'-mi ejected to a distance of 50.000 or 40,000 miles from the surf.-u- in a few minutes. The late 'Mr R. A. Proctor, in his essay, 1 A New Theory of dun Snots’ (‘Longman’s Magazine, 1 April. refers to olwu-vatio-n? made by Pro- \ ounce in 1371 of an eruption f’’om the sun. On that occasion, he writes, “long filament;; of hydro-- m were peon travelling upwards so rapidly that their motions were actually discernible . . . until they had attained tho enormous height of 210.(XX) miles from the min’s visin':' surface.” And from his calculations Mr Proctor determined the velocity with which the matter was ejected on that occasion, at from '3CO to 500 miles a second, lie further pointed out that ihe filaments of hydrogen “ hy no means presented the appearance of bodies rushing with enormous velocity through a resisting atmosphere.” and came to the conclusion that when, duo of (hope h-amonts was -•■’■! apparently advancing with enormous v-.-'.n----cily upwards, what was really happening was this ; “ A solid, or linnid ma-gs wn;

rushing upwards, tearing iL; way tlrmigh v/haU-ver hydrogen lav along its trier, and ibus leaving behind it a trail of glowing !iy-.h‘iij;i*ii. growing at !he miner wwl as the uiis'i’e advanced. ;rv! losing ienrlh at the rear re the ininuitod heat passed away.” In view of the farts stated, he pointed out that it was tolerably obvious that there had been an ejection of matters solid or liquid at velocities so great that the matter could never return to the sun; that a velocity of 360 miles a second was the, greatest that tho sun could control in matter at its surface; and inn * ns the matter ejected probably cross'd the sun’s surface at a speed greatly exceeding this it was now travelling with velocity continually diminishing, but never to bo entirely lost, into the remote depths of interstellar space. He further stated that in 1864 Mr Porby, of Sheffield, was led by the microscopic study of meteors to tho belief, or rather to the conviction, that they had once been cither in the interior of the sun or of a bndv in the sunlike state : while the late Professor Graham was led to a precisely similar conelusion respecting tho Lennrto iron meteor, hv the quantity of iron he found enclosed within its mass. Dr Crommelin, in his work, f Tho Star World,’ gives tho period of maximum sun spots as 11 l-Bth years, just one-ninth of a century. The period is a little more elastic than that. The last maximum was in ISO 6. the last minimum in 1913; a few days will show whether tho maximum is now on or has passed. I have been informed on high authority that sir.ee the last maximum there have been no fewer titan 320 days on which no spots were visible. i According to Mr Serviss, occurrences of Aurora and sun spots occur at the same time, and it is now believed that sun spots cause or encourage outbursts of Aurora. He compares the Aurora to a gigantic exi hibition of vacuum tube lights, and exI presses the view that when the eruptions i take place masses of electrons (electrical . units) arc thrown out from the sun into i space ; that a comparatively small number of these come within the influence of the earth and seek tho terrestrial poles, en- ; countering there a part of the atmosphere : comparable in density with what remains in an exhausted Crookes’s tube, and produce, a glow of cathode rays. In addition to exhibitions of Aurora, magnetic storms take | place in years of many spots, causing ; disturbances in electric telegraphs, magnetic compasses, etc. Dr Crommelin, in the work referred to, quotes Mr Maunder, of the Greenwich Observatory, who is of opinion “ that the disturbed regions of the sun eject tiny electrified particles at enormous speed ; that these travel along definite narrow stream lines like a jet of water from a fireman’s hose. When they enter onr atmosphere they act as the trigger that starts a magnetic storm. The word ‘ trigger ’ is used because it has been proved that the tiny particles could not themselves convey all the energy , that is in play in such a storm ; they are merely the exciting cause; the energy is supposed to come from tho rotation of the earth ” ! INFLUENCE ON WEATHER. ! ft is not unlikely that the sun spots affect tiro weather to some extent, but the evidence is as yet far from convincing, one way or the other. It has been stated on the authority of an article in the magazine ‘ Nature ’ that “ there is a strong probability that Indian famines and tropical cyclones, and even commercial crises in this country (England!, to exactly the same periodicity ” —i.c., the recurring periods of maximum sun spots. Dr Crommelin has pointed out that from observations made by Professor Abbot in California and Algeria there was a decided tendency for tho two stations to agree on the days that gave high or low values, and that there was good reason to think that the sun’s output of energy may vary by 10 per cent, in short periods, and that it was not impossible that some weather changes may be due to this cause. He further stales that Professor Abbot gives j two other interesting conclusions—first, that the solar radiation is increased when ’ spots are numerous; second, that high radiation is accompanied by an increase in

the blueness of tho sun, and therefore by a proportionately loss of light, near ins limb. Dr OommeTin comments: “We know that our earth’s magnetism thrills with response to the sun spot change, and there is some evidence for a change of temperature.” Some readers may be inclined to jump to tho conclusion that the long spell of dry weather which wo have had is attributable to the sun spots in sight of late- It must be borne in mind, however, that the -want of rain (so far as it is known) is confined to parts of Australia, whilst the sun spots, if they appreciably affect the weather, would affect it more or less all over the earth rather than in isolated portions. In fairness to the sun spots, they should not be held responsible for the state of the recent weather, nor even for the prevalent epidemic, in tho absence of any more convincing reason than that they both occurred at tho same time. Tho study of sun spots has led to one curious piece of knowledge as to tho constitution of tho sun. When astronomers began to agree as to the nature of sun spots, it was thought that a simple and ready means had been found for determining tho rate of speed of the sun’s rotation on its axis, By watching the spot when it first appeared on one limb of the sun, and observing the time it took to go across to tho other limb (or, to he more accurate, to bo carried from one horizon to tho other), and there disappeared behind the sun, it was thought that it would be only a -matter of the simplest calculation to fix the period of the rotation. But amazing results followed some of the observations. Judged by spots in the higher altitudes of .the sun, it appeared to rotate in 28 days; whilst judged by spots nearer to the equator, the rotation would appear to take only 24 days. Illustrating this by analogy of the earth, it would he as if those parts of the earth in the latitude of the southern part of England and northern part of France revolved in 28 hours, whilst those in the latitude of India, revolved in 24 hours. Hero was a paradox, apparently demonstrating that the impossible was taking place in view of our eyes. As Mr Proctor pointed out, the real globe of the sun cannot rotate save as a whole and in a single period ; yet, judged by what looks like his surface, his equatorial regions seem to rotate seven times, while the mid-zones of his northern and southern hemispheres rotate only six limes. From this ho inferred that the visible surface of the sun, known as the photosphere (the luminous envelope), is not the real surface, which must lie at an enormous depth below the visible surface. It follows, of course, that the photosphere, the' gaseous envelope, would not be bound by the rigid laws of gravitation to tho, extent that the central body of the sun must conform to them.