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Sun (Center of our solar)
the center of our solar and planetary system, and one of the stars in the boundless sidereal universe. It is a hot self-luminous globe of enormous dimensions as compared with any of its planets, and the source from which they derive their heat and whatever life they bear; but considered as a star it is probably only of moderate dimensions and brilliancy.
Distance and Dimensions. Its mean distance from the earth is about 93,000,- 000 miles, probably a little less, a distance which a fast railroad train would traverse in about 250 years, sound (with its terrestrial atmospheric velocity) in about 14 years, a cannon-ball at 1,700 feet per second in about nine years, and which light flies over in about 500 seconds. Its diameter is about 866,500 miles, nearly 110 times that of the earth. the earth .
With the earth at its center it would take in the whole moon's orbit and have plenty of room for another moon one and three-quarter times as far out as ours and still far inside its surface . Reducing the scale so as to represent the sun by a globe 2 feet in diameter, the earth would be less than 1/4 inch in diameter and about 220 feet away, while the distance of the nearest fixed star on this scale would be about 8,000 miles or the actual diameter of the earth. The surface of the sun is about 12,000 times that of the earth and its volume about 1,300,000 times that of our comparatively small planet.
Mass, Gravity, etc. -The mass of the sun is only about 332,000 times that of the earth, so that its density is only a little over a quarter of the earth's, or about 1.41 times as heavy as water. It is heavy as water. It It is well to keep this in mind in thinking of the probable physical condition of the sun, when we remember that it is largely composed of iron. The attraction of the sun at its surface is about 27.6 times that of the earth at its exterior, so that a 200pound man would weigh about 5,520 pounds on the sun, a body would fall about 444 feet in a second, instead of 16, as here, and a pendulum which marks SUN seconds here would vibrate more than five times per second there.
Rotation and Axis. - The motion of the spots across the sun from E. to W. shows that the huge globe rotates regularly on an axis in a period of about 25.3 days, or rather this is the velocity at the solar equator. On each side the speed is slower, till in latitude 40° the period is more than 27 days. Much beyond this the rotation time is unknown, for the spots seldom extend beyond latitudes of 45° N. or S. The cause of this equatorial acceleration is as yet unexplained path of the spots also shows that the sun's equator is inclined to the plane of the ecliptic at an angle of about 7° 15', and that its axis points very nearly to a point half-way between the stars a Lyræ and Polaris.
Photosphere. The luminous surface of the sun directly visible in telescopes is called the photosphere (Greek phos , "bright"). It is probably a sheet of luminous clouds formed by the condensation of substances which exist as gases in the hotter central mass of the sun. Under a moderate magnifying power it looks like rough drawing paper. With higher powers it looks something like snow flakes scattered over gray cloth.
These flakes or grains are from 400 to 600 miles across, and are probably bright clouds floating in an atmosphere not so luminous. Near the edge of the sun the photosphere is much less brilliant than at the center, due to absorption of the solar atmosphere.
Section of the Sun. - There is an inner nucleus; around it is the photosphere, rising at some places into faculæ and depressed in others in spots . Immediately above the photosphere is the "reversing stratum"; above this is the scarlet chromosphere, with prominences of various forms and dimensions; and over, and embracing all, is the coronal atmosphere, fading gradually away into darkness. Eclipses offer exceptional opportunities for studying the various phenomena of the sun that are outside the central nucleus.
Spots and Faculx. -The most prominent feature of the sun's surface is the spots, some of which can almost always be seen except near the time of a sunspot minimum. They are dark depressions in the photosphere, and consist of a central umbra with surrounding penumbra which is not SO dark. This penumbra consists of radial filaments, and appears like the sloping sides of the sunspot cavity, as if the photosphere were drawn down into the spot by inward currents. In the central umbra there are also sometimes smaller, darker spots, called "Dawes's holes," from the name SUN of their discoverer. The preceding is the description of what may be called a normal spot before it begins to break up; but they are seldom of so regular a character. Frequently there are several umbræ with a common penumbra, and there are sometimes streaks or "bridges" of the bright photosphere extending clear across the whole spot. The umbra is not always central, and the filaments of the penumbra are frequently twisted and curled into the most fantastic shapes, reminding one of swirling tongues of flame or smoke. The diameter of the umbra of a spot ranges all the way from 500 to 50,000 or 60,000 miles.
The whole earth could be dropped into many of them without disturbing the edges. The penumbra surrounding some of the larger groups of spots has sometimes measured as much as 150,000 miles in diameter. The depth of the umbra below the general surface of the photosphere is difficult to determine, but according to the best authorities may range from 500 to 2,500 miles. Surrounding the spots there are generally streaks of the photosphere which are much brighter than its general surface, sometimes extending nearly radially from the spot, and these are called the torch"). They faculæ (Latin fax, "a torch"). They are elevated ridges of the photosphere, and are much more prominent when near the edge of the sun, where they project up through a part of the atmosphere which dims the general photospheric level. The faculæ are not confined to the spot surroundings, but they are much more abundant there. They probably make surgings or upheavals, which are the surrounding accompaniment of sunspot action.
Life and Distribution of Spots. - They begin from insensible points, rapidly growing larger, but generally do not develop the penumbra till after the umbra is well formed. The projection of a bright streak, or facula, across the nucleus of a spot often precedes its segmentation or breaking up into two or more. When a spot disappears it comes about by the encroachment of the photosphere, which seems to fall into and fill the cavity, leaving its place covered by a group of bright faculæ. In the vicinity of a spot the motion of phospheric and other matter is generally inward, toward and down into the center, and occasionally the latter is enough to be detected by the spectroscope. The duration of a spot ranges from a few days to occasionally more than a year, but is generally a month or two. It is a remarkable fact that their distribution is confined to two zones between 5° and 40° SUN Theories of Sunspots. - The cause of spots is not yet satisfactorily made out, and among the many theories offered we can only note that of Faye, who considers them to be cyclonic, like our terrestrial storms, caused by the forward drift of the equatorial photosphere, and the more probable suggestion of Young that they are depressions or sinks in the photosphere brought about by the diminution of pressure below, which would accompany eruptions in the surroundings of the spot, the cooler, darker gases flowing down into the cavity thus formed. Certain it is that they are intimately associated with eruptions and explosions on the surface or from below, but which is cause and effect, or whether both spot and eruption are caused by some outside influence (like the fall of meteoric matter) is as yet undetermined.
Periodicity of Spots. - The spots have, roughly speaking, a period of about 11 years, but it is very irregular and has not as yet received any satisfactory explanation. At the time of maximum the surface is never free from them, while at minimum none may be in sight for weeks at a time.
Effect on the Earth. - The only certain connection between the spots and terrestrial phenomena is that with the earth's magnetism. The range of magnetic disturbance, or storminess, follows the sunspot curve very closely, and individual outbursts on the sun are frequently accompanied by simultaneous "magnetic storms" and brilliant exhibitions of the Aurora Borealis on the earth. The exact mechanical connection between the two is not yet known, but of its reality there is not the slightest doubt. Endless attempts have been made to connect almost every other phenomenon of terrestrial meteorology with the sunspot period, but with the single exception above mentioned none has been satisfactorily established.
Young's Reversing Layer.-Next above the photosphere comes a stratum of unknown thickness, discovered by Professor Young, containing the vapors of many of our terrestrial elements. At the time of a total eclipse, if the slit of a spectroscope is kept just tangent to the disappearing limb of the sun, at the instant of the disappearance of the bright light from the photospheric background the light from this layer flashes out in the spectrum in the shape of bright lines, probably where the dark lines had before been. The point as yet unsettled is whether all the dark lines are thus reversed, and with their relative intensity. Lockyer claims that this so-called layer is of a considerable height, and that at SUN different heights in it, different lines, or the same lines with different intensity, will appear, in accordance with his theory that in the sun our chemical elements are dissociated and float at different levels in the solar atmosphere. This is one of the points to be settled by observation at future eclipses.
Chromosphere and Prominences or Protuberances. - Above the reversing layer and interpenetrating it, or possibly identical with it, if Lockyer's theory should prove true, is an atmosphere of permanent gases called the chromosphere. Hydrogen is the most abundant of these gases, and out of this chromosphere rise the wonderful prominences or protuberances which form so prominent a feature of the sun's surroundings at the time of a total eclipse, and which can be investigated by the spectroscope at any time as they consist almost wholly of hydrogen. They are of all imaginable fantastic shapes, and frequently rise, and are sometimes seen to be rapidly projected to the height of several hundred thousand miles, and at enormous velocities. In such case they are almost always seen to be connected with some active sunspot, and they are unquestionably the results of the upheavals, eruptions, or explosions accompanying the surroundings of the spots. ts. The chromosphere itself all along the limb of the sun, as seen in the hydrogen lines in the spectrum, is not a smooth, flat layer, but consists of filaments like upward tongues of flames, and has been compared to the appearance of a "prairie fire," though there is no actual combustion going on.
Spectrum and Constitution. Almost all our knowledge of the constitution of the sun has been revealed to us by the spectroscope. It has shown us that not only do many of our so-called chemical elements exist in the sun, but that its temperature is so high that they exist there in the form of gases. Among the elements identified are hydrogen, iron, titanium, calcium, manganese, nickel, cobalt, cobalt, chromium, barium, sodium, magnesium, and platinum, with a strong probability in favor of copper, palladium, vanadium, molybdenum, uranium, aluminum, cadmium, carbon, and lead. With the exception of carbon all the above are metals. (Hydrogen in its chemical relations ranks as a metal.) A few years ago it was considered that the late Dr. Henry Draper had shown the strong probability of the existence of oxygen in the sun, but the later investigations, while not decisive, tend to negative this conclusion. In this connection SUN Mr. Lockyer's views must be mentioned.
He considers that none of our so-called chemical elements are truly elementary, but that they may all be decomposed into simpler constituents, and that many of them are so dissociated in the sun and the stars. The matter is still one of the most important unsettled questions in the domain of astro-physics. A full exposition of his views may be found in his "Chemistry of the Sun." The revelations of the spectroscope in regard to the chromosphere, prominences, and so-called reversing reversing layer layer have already been briefly mentioned. It has also been instrumental in revealing the enormous velocities accompanying explosions, and eruptions on the sun. At the limb of the sun we see these revealed by the telescope directly in the huge hydrogen prominences, but the spectroscope shows another component of this velocity in the direction to or from us in the line of sight. In the spectrum of a spot, and of the faculæ round it, the lines are frequently broken and twisted into remarkable shapes, indicating motion to or from us of the gases in question at enormous velocities.
In some cases hydrogen has been shown to be rushing toward us with a velocity of 300 miles per second. Occasionally the spectrum of the nucleus of a spot has shown a down-rush of matter into the cavity.
The Solar Corona. - Surrounding all other parts of the solar surface rises the halo of light called the corona, which is only visible at the time of a total eclipse.
Though known from the remotest times, little is yet known of its cause or physical condition, and it is the principal object of attack now at the time of every eclipse of the sun. Down near the surface it is very bright and of a pearly or greenish color. Above this it rises, especially at the poles, in short, finely clustered filaments. Over the sunspot zones it generally rises higher in broad streaks, and at times extends out nearly in the direction of the ecliptic in faint streaks looking like gauze wings on the sun. These fade out gradually, and their limit to the eye or the photographic plate is fixed by the brightness of the sky background. Up in the clear air of Pike's Peak, Col., in 1878, these streamers were seen extending at least 9,000,000 miles from the sun. It varies much at different eclipses and is never twice alike, though certain typical forms seem to follow somewhat the maxima and minima of the sunspot period. The total light of the corona is at least two of three times that of the full moon. As its light appears to be relatively rich in the ultra violet part of its spectrum, Dr. Huggins SUN has attempted to photograph it in full sunshine, bu but thus far it is somewhat doubtful if he has succeeded in this.
The spectrum of the corona consists principally of a bright line in the green which has not been identified with that of any terrestrial element, and for which the name coronium has been proposed.
The lines of hydrogen are also visible, but not so bright by far as the line in the green. There is also a faint continuous spectrum, and some observers have claimed to see on this the faint absorption lines of the solar spectrum.
The nature of the corona is one of the most puzzling things to explain. It cannot be an atmosphere in any sense of the word, as the gaseous pressure there must be less than that of the most perfect vacuum we can make. Comets sweep through it without hindrance. It is a product of some sort of the enormous forces at play in the vicinity of the sun.
Meteoric matter, cometic matter, matter ejected from the sun, are probably all concerned in it, and possibly electricity may play some part in the display. It is possible, and indeed perhaps probable, that the zodiacal light which reaches far out toward and perhaps beyond the earth's orbit, is a faint extension of the equatorial coronal streamers.
Radiation. Compared with other familiar sources of light we find that the amount of it received from the sun is about 600,000 times that from the full moon, 7,000,000,000 times that from Sirius, 40,000,000,000 times that from Vega or Arcturus, and 1,575,000,000,000,- 000 times as much as a standard candle would give at the distance of the sun. The intrinsic brightness of its disk is about 90,000 times that of a candle flame, 150 times that of the lime in a calcium light, and from two to four times as bright as the brightest spot in the crater of an electric arc light.
The darkest part of a sunspot is brighter than the lime light. The brightness of the sun's surface near the edge of the disk is only about one-third that at its center and is of a brownish-red color.
This makes it appear still fainter at the edge of a photograph of the sun. If the sun were stripped of its atmosphere it would probably shine from two to five times as brightly as at present, and would be of a decidedly blue color. Considering solar radiation in its heating effect and measuring it in terms of its power to melt ice, we find that the total amount of heat received annually would melt a sheet of ice 174 feet thick at the equator, or 136 feet thick over the whole surface of the earth if the radiation were equally distributed in all latitudes. Con- SUN verted by means of the mechanical equivalent of heat and expressed as energy, we find that, neglecting the absorption of our atmosphere, each square meter of the earth's surface would receive from an overhead sun about two and onethird horse power continuously. Atmospheric absorption cuts this down to about one and a half horse power. Transferring ourselves from the surface of the earth to that of the sun, and considering the radiation per unit of surface there, the figures are enormous, and the energy in question is almost incomprehensible.
Every square meter of the sun's surface is continuously radiating more than 100,- 000 horse power. A shell of ice 50 feet thick would there be melted in one minute. To keep up such a development of heat by combustion would require that a layer of the best anthracite coal over the whole surface from 16 to 20 feet thick should be burned each hour, a ton an hour for every square foot of surface, at least nine times as much as the consumption of the most powerful blast furnace per foot of grate surface. At this rate the sun, if made of solid coal, would not last 6,000 years. Of this enormous amount of energy, so far as we know, only about .000,000,001 is intercepted and utilized by all the bodies of the solar system, and to the best of our knowledge, and according to human ideas, the rest of it goes to waste.
Temperature. - While we can measure with a fair degree of accuracy the amount of solar radiation, the determination of the actual temperature of its surface is a very different matter. All that can with certainty be said is that it is much higher than any temperature that can be pro produced by terrestrial means. The various estimates have taken the widest possible range, depending on the assumed law connecting radiation with temperature. The most reliable estimates place the probable effective temperature as something like 10,000° C., or 18,000° F. There must also be a considerable range of temperature at different depths below its surface. Sources of Energy. We have noted the tremendous expenditure or energy by the sun in the form of radiation. A natural question is, How does it keep it up? We have mentioned the insufficiency of any combustion hypothesis. The only others worth mentioning are the meteoric and the contraction theories, as it can easily be shown that the theory of a cooling sun will not suffice, since, if this were the source of its radiant energy, it must have cooled enough within historic times to have affected very decidedly its Ewing Galloway A SPONGE WHARF AT KEY WEST, FLA.
Enc. Vol. 9-p. 164 Publishers' Photo Service STALACTITES AND STALAGMITES IN THE BELLAMAS NATURAL CAVES, MATANZAS, CUBA Underwood & Underwood PLANTING SUGAR CANE ON IRRIGATED LAND IN PERU Underwood & Underwood SUGAR CANE GROWING ON A PLANTATION IN LOUISIANA Ewing Galloway SUGAR CANE READY FOR HARVEST IN THE ISLAND OF JAMAICA, WEST INDIES Underwood & Underwood THE INTERIOR OF A SUGAR MILL IN CUBA. AT THE LEFT ARE VACUUM VATS IN WHICH THE JUICE IS BOILED BEFORE ENTERING THE CENTRIFUGAL MACHINE Underwood & Underwood A SUGAR LEVEE, NEW ORLEANS, LA.
International Film Service A GERMAN SUBMARINE, THE CREW OF WHICH IS SURRENDERING TO THE AMERICAN DESTROYER "FANNING" SUN radiating power. The meteoric theory attempts to account for the keeping up of its supply of energy by the fall of meteoric matter into the sun. A body falling into the sun from any considerable distance will generate by the sudden arrest of its energy of translation an enormous amount of heat, 6,000 times as much as would be generated by its complete combustion if it were a mass of pure carbon. From the fact that meteors are constantly striking the earth we know that they must be all the time fall ing into the sun, but nevertheless the greater part of the meteoric matter in the vicinity of the sun must circulate round it as the comets do. The most careful estimates seem to indicate that only a very small fraction of the sun's radiant energy can come from the fall of meteors into it. The only sufficient theory left is that of Helmholtz the contraction hypothesis. Without going fully into the explanation of this it may be briefly stated that, supposing the bulk of sun to be mainly gaseous, a contraction of about 250 feet per year in its diameter would supply all its present rate of radiation. At this rate it would take nearly 10,000 years to diminish its apparent diameter by a single second of arc, and it is doubtful if this amount could be certainly determined with our present means of measurement of this diameter.
Age and Duration. - Everything points to the conclusion that the present condition of the sun is mainly gaseous, and its future supply of heat depends on that condition. The contraction can only keep up its temperature so long as it is principally in a gaseous state. As soon as any large part of its bulk liquefies (only the thin shell of photospheric clouds is now supposed to be in a liquid condition), it will begin to cool off and its temperature will fall. This means the beginning of the end for life on the earth. The best estimates place this time as not more than 5,000,000 to 10,- 000,000 years off at the longest. The past history of the sun is involved in about the same obscurity as the nebular hypothesis. Certain data can not be furnished with exactness. Knowing the mass of the sun, we can compute how much heat has been generated in its condensation from infinite space or from any assigned dimensions; but as to the rate at which this heat has been radiated in the past ages, and the rate at which contraction has taken place, nothing definite can be stated. It may be considered that the age of the solar system is entirely unknown.