SUN SPOTS IN WAR YEARS.

Pukekohe & Waiuku Times, Volume 6, Issue 274, 11 May 1917, Page 4 (Supplement)

SUN SPOTS IN WAR YEARS.

SOLAR CYCLONE WHICH TRAVELS TWO MILES A SECOND.

By EDWARD WALTER MAUNDER (Fellow of tho Royal Astronomical Society.)

(Mr. Maunder was superintendent of the Solar Department at the Royal Observatory, Greenwich, from to 1913, when he retired. For the past year he has been doing war-time duty at tho Observatory.)

Tho sun-spots which have attracted public attention recently are among tlio larger that have boon observed. Their area has been nearly four million square miles, or al>out 1,1)00 times the area of Europe. Twelve years ago wo had a spot-group that was quite four thousand million square miles in area. Exactly what a sun-spot is, it is not easy to explain. The sun's surface is in tho nature of a luminous cloud, not of water vapour liko our -clouds, but of the condensation of carbon and ether very refractory elements. A sun-spot is evidently an interruption or breach in this luminous cloud, and in the spot thoro seems to us lwth an upward and downward rush. The tomporaturo in a sun-spot i.i considerably lower than the temperature in its neighboudhood. We know this l>ocauso the spectroscopo shows us tho presence in a sun-spot of 'Certain compound substances which could not exist at the high tomporaturo of tlie general surface of the sun, which is about 12,000 degrees Fahrenheit. Tho sun's temperature is evidently higher in the interior than in the outer portions which radiate their heat through space. Consequently, if thoro i;, a violent explosion in tho sun, there will be highly heated gases thrown up from below, and much cooler gases drawn down into tho vortex. We have io experience of any conditions on tho earth which would give us a valid idea oi tho -condition,; in the sun's interior. Wo cannot reproduce such a temperature as 12,000 degrees Fahrenheit, and wo cannot reproduce such pressures as exist in the sun. Wo know that the sun i s lighter in weight than the earth, bulk for bulk; its density being only a quarter of tho earth's density.

BRIDGES OF LIGHT

I have spoken of an "explosion," but the word gives but little definite idea of what goes on in a sun-spot. Nevertheless-, tho action that goes on in the neighbourhood of a big sunspot is exceedingly violent and the word "explosion" gives us some suggestion of what happens. In these particular sunspotw the changes have been very rapid. Bright " br'dges "of light have been seen stretching right across the spots and bright points appearing in and arcund them, and when tho spot-group reaches the circumference of the sun we shall see a number of prominences, or tongues of glowing gases rising for thousands cf niileii above the sun's- surface-

What may bo said is that the sunspots arise from some internal change in the sun, and may bo duo to the gradual process of cooling which we suppose to be going on in tho sun. At times tho sun appears quiescent. In 1913 it was as quiet an it ever is. From the beginning of 1914 it has gradually been growing more disturl>cd. It is extremely l'kely that we shall havo a very disturbed year in the matter of sun-spots.

Wo may obtain a bettor idoa of a sunppot, perhaps, if wo compare it with our terrestrial storms. Our atmosphere seems about tho most fluid tiling we know, but a certain amount of viscosity exists in it, ;;nd it does not immediately rectify small differences in barometric pressure, birt they tend to accumulate until a more or loss violent storm sets in, and tlie venditions right themselves-.

8,000 MILES A DAY

If you imagine these movements transferred to the sun, with its enormously higher temperature and immense pressures, it in clear that it must po». so.** greater viscosity than our atmosphere, but that wlion violent action comes it will lo immensely more violent than terrestrial storms.

Our cyclone may be taken as the nearest terrestrial analogy to a sunspot, but our n:o->t terrific cyclones are mild as a May morning compared with tho violence of sun-spots, in which the g.is<>s often move at the ratoof from 100 to 200 miles in one second, as measured by tho specterscope. Sun-spots within tho same group will move away from with other at the r;ito of about two miles a second.

Tho typical stinkpot usually starts with two Pn_v dots. These move apart at the rate of motion cf about S,OOO miles a day. or a little over two miles pi second. They keep this up for some tune, and grow as they move al>out, while smaller spots form.between them, making a long stream of spots, of which the two original are the Larger. The solar clouds in their incvgliboufliood evidently heap up round the group and float over the middle of the stream, blotting out the smaller spots. Then tho rear spot gradually breaks up, and tho leader spot is left alone.

BOILING OVER. Sun-spots appear to l>e duo to Rome rhythmical act'on inside tho sun, like tho periodical boiling over of a pol, damping for a time tho firo under it, or, as 1 liavo said, like terrestrial disturbances due to changes in atmospheric pressure. Their influence takes a little more than twenty-four hours to reach the eart/i, compared with tho eight minutes occupied by the sun's light and heat. It is .-low compared with light, hut quick compared with the motion of tin- earth, for while tho earth travels at tho rate of G7.000 miles an hour, the influence of the sun-spots tarvols to tho earth at tho rate of nearly four million miles im hour. Through what medium does tho influence of sun-spots reach the earth ? Tho tiun sends out streams of very minute electrically charged particles Irom certain points of it-> mrfaee. Light and heat come from tho whole of the sun's surface and are radiated in nil directions, hut these electrically charged streams travel only in partiewlar directions. When they overtake the earth, as they occasionally do, they influence the earth's magnetism, just as a galvanometer would lie d'stutbed by an electric current. The greatest magnetic storms have made the magnet swing two degrees, which is an appreciable amouint, hut lh« ordinary magnetic • disturbance is much smaller. 1 have studied "iin-spots to sea whether there, is any connection between them and nor Hr'ti*-li weather, from the point of view both of tempcra-t-ure and of rainfall, and I have fi und that wo have hail i ut -'immcs ''pd cold summo: nid rlry and Wi- - weather :'•'- mr.i, indifferently, with miny Min-«pots or few or none.