Solar atmosphere

“ It is because the atmosphere of the sun is cooler than the globe it envelops that the different kinds of vapour constituting that atmosphere take more than they give, absorb more light than they are capable of emitting; raise them to the same temperature as the sun itself, and their powers of emission and absorption being brought exactly to the same level, the thousands of dusky rays in the solar spectrum will be at once obliterated. ”

“ If the temperature of the solar atmosphere were rapidly raised by increased planetary action to a point which would reverse the lines of hydrogen from dark to bright, say to a brightness eight hundred times that of the normal, as in the case of the temporary star cited, though the heat would not, of course, be increased in any such proportion, yet the heavens would be indeed rolled up as a scroll, and all life would be extinguished in a very brief period. ”

“ Sun-spots of considerable magnitude have been observed to grow rapidly and then disappear in a very short period of time; occasionally a spot is seen to divide into two or more portions, the fragments flying asunder with a velocity of not less than 1,000 miles an hour. It is by these upheavals and convulsions of the solar atmosphere that the light and heat are maintained which illumine and vivify the worlds that gravitate round the Sun. ”

“ The solar atmosphere has been found to extend to more than half a radius beyond its surface; at the top of its corona, high above the hydrogen, there are vast masses of a gas which emits a simple, green ray, not corresponding with that of any known substance. ”

“ From the fact that one half of the atmosphere, including nearly all of its water vapor, lies below an elevation of three and one half miles, it becomes evident that the greater part of the absorption of the sun’s rays must take place in the lower strata. On clear days the atmosphere absorbs nearly one half of the sun’s heat rays; the remainder reaches the surface of the earth, warms it and in turn is radiated back into the air,—with this difference: that as earth radiation the wave motion of the rays is longer and slower than it was when the rays entered our atmosphere as solar radiation. ”

“ All regions of the sun's disk radiate heat uniformly, and the sun's own atmosphere absorbs so much that we should receive 1.7 times more heat if it were removed. So far as is known, solar light and heat are radiated equally in all directions, so that only a very minute fraction of the total amount ever reaches the earth, that is, 1 2200 millionth part of the whole. ”

“ We see, in short, that this atmosphere is livelier in its action in the two zones on each side of the equator, in which the spots ordinarily show themselves. The existence of a solar atmosphere being perfectly in accordance with all known principles and with all ascertained facts, there is no longer any room for calling it in question. We describe the sun, then, as surrounded by a dense atmosphere in which floats the photospheric matter. The surface of the photosphere is far from being uniform and regular. ”

“ This scattering action of the atmosphere on the solar light is greatly increased by the irregularity of temperature caused by the sun, which throws the atmosphere into a constant state of undulation; and by thus bringing together masses of air of different temperatures, produces partial reflections and refractions at their common boundaries, by which means much light is turned aside from a direct course, and diverted to the purposes of general illumination. ”

“ Does the planet radiate heat of the wave-lengths that it receives from the sun? and how is its temperature maintained, probably several hundred degrees above the temperature of space, when our observations show that the direct radiations of heat from the sun can only raise it about fifty degrees above the surrounding temperature? Experiments at Allegheny show that the dark solar heat is transmitted by our atmosphere with less difficulty than the light ”

“ Our atmosphere is a mixture of gases and aqueous vapour; and it has been found, as already stated, that even a thin film of water, however transparent, prevents the passage of many calorific radiations, and the rays retarded are, for the most part, of that class which have this peculiar scorching power. The air is, in this way, the great equaliser of the solar heat, rendering the earth agreeable to all animals, who, but for this peculiar absorbent medium, would have to endure, even in our temperate clime, the burning rays of a more than African sun. ”

“ They must be cool, for at the planetary poles there must be a moderate temperature in contrast with the solar pole, which becomes, of necessity, highly heated; they must have an atmosphere of oxygen in order that the solar center may have an atmosphere of hydrogen ”

“ As soon as the Sun has disappeared below the horizon all the clouds overhead continue for a few minutes so highly illuminated as to reflect scarcely less light than the direct light of the Sun. As, however, the Sun gradually sinks lower and lower, less and less of the visible atmosphere receives any portion of its light, and consequently less and less is reflected minute by minute to the Earth at the observer’s station until at length the time comes when there is no sunlight to be reflected—and it is night. ”

“ The intensity of solar radiation increases rapidly with increasing elevation,54 so that when the sky is clear surfaces exposed to the sun are heated much above the normal temperature. Owing to its slight absorptive power the free atmosphere is little affected; but the strata nearest the surface are heated by convection, while a contrary effect follows when the surface is no longer exposed to the sun, and radiates freely to the sky.
The air in mountain countries is rarely at rest. ”

“ The Sun is a sphere, and is surrounded by an extensive but attenuated envelope, or rather series of envelopes, which taken together bear some analogy to the atmosphere surrounding the Earth. These envelopes, which we shall have to consider more in detail presently, throw out rays of light and heat to the confines of the Solar System, though as to the conditions and circumstances under which that light and heat are generated we are entirely ignorant. ”

“ The exterior stratum cools itself constantly by radiation, passes into the gauze-like state, or state of vapor, and ends by precipitating itself in the liquid state, or even in the solid, remaining, however, suspended in the solar atmosphere, as clouds do in ours. It is this condensed matter that forms the photosphere, and it is from that principally we receive light and heat. ”

“ WHAT we see of the sun under ordinary circumstances is but a fraction of his total bulk. While by far the greater portion of the solar mass is included within the photosphere, the blazing cloud-layer which seems to form the sun's true surface, and is the principal source of his light and heat, yet the larger portion of his volume lies without, and constitutes an atmosphere whose diameter is at least double, and its bulk therefore sevenfold that of the central globe. ”

“ The condensation of volume of the planets will give rise to great elevation of temperature, while their currents of electricity, poured into the sun, will, by their passage through its enormously compressed hydrogen atmosphere, produce intense heat, and this, rapidly communicated to the solar core within, will raise its temperature to that of the sun as we now see it, and permanently maintain it in that state of incandescence. ”

“ Now, it happens that we know quite well that the pressure exerted by the real solar atmosphere, even close by the bright surface which forms the visible globe of the sun, is nothing like so great as it would be if the corona formed part of that atmosphere. ”

“ Now, as it is admitted that our dense atmosphere, however dry and clear, absorbs and reflects some considerable portion of the solar heat, we shall certainly underestimate the radiation from the moon's surface during its long night if we take as the basis of our calculation a lowering of temperature amounting to 100°F. during twelve hours, as not unfrequently occurs with us. ”

“ Cope Whitehouse, to the effect that the sun is not really a hot body at all, and that what we call solar light and heat are only local manifestations produced in our atmosphere by the transformation of some other form of energy transmitted from the sun ”

“ During its annual revolution this planet will traverse, with its line of energy, every point of the sun’s surface down to seven degrees south latitude and back again to its initial point, thus tracing a close spiral around the sun for fourteen degrees, or about one hundred and four thousand miles in width. The centrifugal force of the solar rotation piles up the photosphere and the chromosphere around the sun’s equator, precisely as our atmosphere is piled up around our own equator. ”

“ And we are enabled, knowing the increasing rarity of the upper regions of our gaseous envelope, in which the absorption is constantly diminishing, to prove that about one-third of the solar heat is lost by vertical transmission through the whole extent of our atmosphere.—J. D. Forbes, F.R.S. ”

“ If the constitution of the Sun be that which is above inferred, it does not seem difficult to conceive still more specifically the production of these appearances. Everywhere throughout the atmosphere of metallic vapours which clothes the solar surface, there must be ascending and descending currents. ”

“ By fixing our attention on the sun himself, the source of all energy here below, we run less risk of being led astray. For example: do we find, in known solar phenomena, any reason to believe that the Sun has other means of action besides his attraction, his heat, and his light? The answer, "Yes," is ready. The Sun possesses and exercises a plainly-marked repulsive power, of which meteorology has hitherto taken no account, although our atmosphere must experience its effects. ”

“ We shall also find in such electric currents an explanation of sun-spots. It is not meant that a full knowledge can be obtained of their minute constitution, nor is it necessary; but the equatorial belt of six degrees, nearly free from sun-spots, we can readily understand to be caused—since sun-spots are depressions in the photosphere down to the deeper and denser cloud strata beneath—by the equatorial piling up of the sun’s atmosphere by its rotation. ”

“ As the moon now proceeds towards her first quarter, the terrestrial repulsion drives her atmosphere radially outward, while solar gravity and electrical attraction tend to hold it in the direction of the sun. ”

“ The diagram drawn by Professor Müller to represent the distribution of heat in the solar spectrum is not by any means so striking as that just described, and the reason, doubtless, is that prior to reaching the earth the solar rays have to traverse our atmosphere. ”

“ The absorption of solar radiation by the atmosphere is apparently explained by the laws of diffuse reflection, selective diffusion and fluorescence in accordance with which each atom and molecule and particle becomes a new centre for the diffusion in all directions of the energy represented by some specific wave-length. ”

“ The transmission of solar radiation through the earth’s atmosphere is the fundamental problem of meteorology, and has been the subject of many studies, beginning with J. H. Lambert and P. Bouguer. The pyrheliometer of C. S. M. Pouillet gave us our first idea of the thermal equivalent of solar radiation outside of our atmosphere or the so-called “solar constant,” the value of which has been variously placed at from 2 to 4 calories per sq. ”

“ Speaking loosely, it may be estimated that at the sea-level, in fair weather, neither excessively moist nor dry, about thirty per cent, of the solar radiation is absorbed when the sun is at the zenith, and at least seventy-five per cent, at the horizon. ”

“ Let us apply this principle to the solar system, and endeavour to find out whether in that system we have, in relation to the heat thereof, either a cycle of operations or a reversible cycle. We have again to consider the sun as the source of all light and heat in the solar [118] system, radiating forth on every side, year by year, the countless units of heat which go to form the continuance of all planetary life and existence. One of the problems that has confronted scientific men for many years is this, Where does the sun get its supply of heat from? ”

“ The mean value which has been arrived at is fourteen, and the fundamental fact with regard to the solar radiation which we are thus enabled to state is that an area of a square foot exposed at right angles to the solar rays, at a distance of 93 millions of miles, will in each minute receive from the sun as much heat as would raise one pound of water fourteen degrees Fahrenheit. ”

“ They are the means provided to distribute the restricted areas of abnormally heated photosphere over the solar surface, and finally to cause the absorption of the whole excess of heat in the sun’s central mass. ”

“ The sun spots are the most extensively studied and the least understood of all solar phenomena. That they are large-scale interruptions in the photosphere, and at the same time the most striking evidence of atmospheric circulation, there can be no doubt. Observations made near the sun's limb, to determine whether the spots are elevations or depressions with reference to the photosphere, seem not to be reliable, perhaps because of abnormal refractions in the strata overlying and surrounding the spots. ”