OUTBREAK IN THE SUN

Taranaki Daily News, 4 March 1933, Page 13 (Supplement)

OUTBREAK IN THE SUN

WHAT ARE SUNSPOTS?

(By

Rev. B. Dudley,.

F.R.A.S.)

After a period of comparative calm the sun has developed a state of disturbance which manifests in a series of spotgroups of considerable magnitude. These have been visible for a week or more. Seen in a pair of binoculars, cautiously screened from the dangerous glare and heat produced by unprotected lenses, they present the appearance of lengthened gashes forming a sort of procession, while the telescope reveals many smaller spots. There are also scores of “pinnacles” a thousand miles or less in width. A rough measure of the largest of these groups taken at the time of writing shows it to be from 290,000 to 310,000 miles long, while the diameter is rather more than 85,000 miles.

In a few days’ time these spots will have been carried round to that side of the sun turned away from the earth—borne thither, that is to say, by the solar rotation. Here they may die down and finally disappear altogether, or persist and reappear in due course on the eastern edge of the sun, once more to cross his face.

It is the movements of sunspots more than anything else that has proved the fact that the sun, like the earth, turns continually upon its axis. Although these spots have small movements of their own on the sun’s surface, it was found by Scheiner, as long ago as 1627, that “the various spots all partake of a common movement, whiqh could not be accounted for by the supposition of any proper motion in the spots themselves.” It is now known that the sun revolves on an axis which is nearly at right angles to. the plane of the earth’s orbit in a period of about 25 days, the spots near the equator travelling faster than the general axial whirl of the sun. It should, however, be stated 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 the equator rotate in about 25 days, those situated between 20 and 30 degrees of the sun’s eauatorial latitude require 26, and those which belong to a zone 40 degrees from the' equator require 27 days to perform a revolution. Those parts of the sun’s surface situated within 15 degrees of the poles require 30 days for a revolution. All this goes to prove that our “light by day” is not a solid body. The same condition of things obtains in the yet hot and plastic planet Jupiter, which is just now so conspicuous an object in our late evening and early morning skies. Spots are seldom seen more than about 35 degrees north or south, and are rarely found in the regions of the equator itself.

In connection with the present groups there are to be seen- the usual accompanying display of faculae, consisting of bright elevated streams surrounding the groups of spots and extending some distance beyond. They are believed to be the tops of clouds of vapour rising from the sun, and they are probably connected with the tremendous red flames or “prominences” which leap up from its surface to a height of many thousands 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 forms, having quite distinct outlines, and either separate or uniting in various traceries into ridges and network. They may be of varied extent, from almost indiscernible, softgleaming strips 1000 miles long, to enormous ridges more than 40,000 miles in length, and from 1000 to 4000 miles broad. Faculic markings may be seen all over the sun’s surface, but are more abundant in the vicinity of a spot or spot-group.

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 more than 2000 miles deep.

Sunspots. are found to be a most fascinating study in small as well as large telescopes. But notwithstanding the prolonged and minute attention which has been devoted to them for many years past by experts, their exact nature is still very largely a matter of mystery. Even the refined and ingenious processes which are now employed in their examination are incompetent to so analyse 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 spectroheliograph 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. Sunstorms (for such the spots really are) are not usually felt by us to any appreciable extent until they reach the middle regions of the sun’s disc. On passing that phase they sometimes give rise to sympathetic electrical and magnetic disturbances on the earth. The spot groups of the present time passed that central position a few days ago. Only in a general sense can it be claimed that the sun determines the weather upon the earth. If one may so put it, sun-weather affects and in some degree determines world-weather. So many local circumstances and conditions modify the direct influence of the sun—circumstances and conditions which overlap and interchange and moderate or intensify each other —that it will probably be a long time ere science will have advanced to such a stage as to render it possible to disentangle and estimate these interpenetrating and conflicting forces and foretell what weather conditions will prevail in any district, country or area. It is something to know this, even though the knowledge may disappoint those who would see established a forecasting system based on the intimate association of the magnetic conditions of the sun and of the earth. It looks as if, in this matter at any rate, we shall have to be content for the present with truth for its own sake—a blessed form of contentment.

The whole question of sunspots is highly complicated and astronomers, feeling that much is involved in a solution of it, are not slack in their attention to the subject. ' For a number of years past there has been an organisation at work in several observatories 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 missed.. . .