SUN HAS SELDOM BEEN SO AGITATED.

Star (Christchurch), Issue 17978, 15 October 1926, Page 6

SUN HAS SELDOM BEEN SO AGITATED.

“ PROCESSION OF SPOTS ” MOVES OVER SURFACE

By

DUDLEY, F.R.A.S.

The writer of this article has for many ye&rs taken frequent instrumental observations of the sun, and closely noted the sunspot features, but has never seen anything like the present condition of the solar surface. What may be 6poken of as a “ procession of spots ” stretches right across the sun’s disc. Six large, dark centres, surrounded, or accompanied, by numerous smaller ones, all in a slightly curved line, present an imposing appearance in the sceened field glass or telescope. In addition to this almost equallyspaced stream, there are two other smaller spots, one a group, the other a mere “ pinhole.” which might be no more than 1000 miles across. The larger ones are approximately from 25,000 to 30(000 miles in diameter. At the two extremes, one group' is about to retire to the side of the sun turned away from us, while another is just coming into view on the visible hemisphere, all being, of course, carried round with the sun’s rotation. Three or four of the groups are “ trailers,” each centre being followed or preceded by a train of pinhole spots. The distinction between the umbral and penumbral portions is well marked in most of them. Some of the umbrae are bridged across with over-shooting faculic streams. The whole indicates that the sun is at present in a greatly agitated state such as is sure to be reflected by extraordinary terrestrial weather conditions. It is the motion of sunspots more than anything else that has proved the fact that the sun, like the earth, turns continually upon its centre. Although solar spots have some amount of independent motion, it was found by Scheiber, as long ago as 1627, that “ the various spots all partake of a common movement, which could not be accounted for by the supposition of any proper motion in the spots themselves.” It is in fact known that the suq turns on an axis which is nearly at right angles with the plane of the earth’s orbit in a period of about twenty-five days, and that the spots near the solar equator travel faster than the general axial movement of the sun. It should be stated, however, that the period of rotation, as indicated by the motion of the spots, is not the same for all portions of the solar surface. While spots at or near the equator complete a circuit round the sun in abount twenty-five days, those situated between 20 and 30 degrees from the sun’s equatorial latitude require twenty-six days, and those located on a zone 40 degrees therefrom require twenty-seven days to perform the revolution. Those parts of the sun’s surface situated within 15 degrees of his poles require thirt}*-six days for a revolution. All this goes to show that the great luminary is not a solid body. Spots are seldom seen, however, more than about 35 degrees north or south, and are rarely found actuary on the equator itself. The average speed with which sun spots move across the solar disc is a little more than fifty miles a minute. It should be remembered that the diameter of the sun is 863,000 miles. In connection with the present sun spot groups there are to be seen the usual accompanying display of faculac, consisting of bright. elevated streams. They are believed to be the tops of clouds of vapour rising from the sun, and are probably* connected with the tremendous red flames or “prominences” that leap up from his surface to a height of many thousand's of miles. The faculae are the more brilliant parts of the sun; and when in the neighbourhood of a spot, it is ' not difficult, even with a small telescope, to detect their diversified form, having quite distinct outlines, and either separate or unite in various ways into ridges and network. They may be of varied extent, from almost indiscernible. softly-gleaming strips 1600 miles lone, to enormous ridges over 40.000 miles in length, and from 1000 to 4000 miles broad. Such ridges are seen surrounding one of the present spot-groups. Faculae exist ajl over the sun's surface; but are more marked in the vicinity of a spot. The penumbra surrounding or enclosing the darker umbra appears like a steep cliff sloping downwards on to ! it. This is a general characteristic of solar spots, the sloping penumbrae being sometimes over 2000 miles deep. Sunspots are found to be a most fascinating study in small as well large telescopes. But notwithstanding the prolonged and minute attention that has been devoted to them for many years pa-~t by experts, their exact nature is scill very largely a matter of mystery. Even the refined and ingenious processes which are now employed in their examination are incompetent to so analvse them as to extract their secret. It is evident, however. that they are openings in the photosphere, or luminous envelope of the sun, .from which the bright cloudlets have been temporarily removed, exposing the comparatively dark interior. The writer has sometimes witnessed the inner edges of a spot as it were melting and falling in. By means of the spectro-heliograph pictures One may see how the masses of hydrogen and calcium vapours which lie above and around them are whirled in vortices. But whether a sunspot represents an uprush of heated matter from within, or a downrush of cooled gas from above, still remains uncertain. In any case, sunspots are taken generally as indicating an activity which is not merely superficial, but which affects the structure and functions of the Sun storm (for such the spots really are) are not Usually felt by us to any great extent, until thev reach the mid die regions of the sun s disc. On passing that phase they sometimes give rise to sympathetic electrical and magnetic disturbances on the earth. At the present time the sun is fast approaching a condition of maximum disturbance. This will be reached (in keeping -with the well-known elevenyear cycle from maximum to maximum) in 1925-9. There will meanwhile doubtless be storms and floods and earthquakes on earth. The whole question is highly complicated, and astronomers, feeling that much is involved in a solution of it. are busy with their tasks in this direction, for many years past there has been an organisation at work in England and elsewhere by which the sun has been photographed every day. Weather being unfavourable in one place. it is sure to be suitable in another, and ’ thus long and continuous observation . is now practicable, and nothing is miss ed, while the number and area of the spots are being faithfully recorded for , future study and reference, j Observers with field glasses, etc. 1 should on no account fail to use a deep ly tinted or smoked glass. Serious in I jury to vision is possible without such j a screen.