Interstellar dust

“ When the heat subsides, the vapor condenses again into fine dust, so that the ultimate effect of the atmosphere on a shooting star is to grind the little object into excessively fine powder, which is scattered along the track which the object has pursued. Sometimes this powder will continue to glow for minutes after the meteor has vanished, and in the case of some great meteors this stream of luminous dust in the air forms a very striking spectacle. ”

“ Aratus, the Greek poet, claims that the sparkles of light which twinkle in this vicinity are particles of dust which the hero stirred up in his haste to rescue Andromeda.
"His giant strides the blue vault climb and move
A cloud of dust in heaven." What a charming picture to impress upon the sky!
But now in the twentieth century we analyze this dust which the ancients claim their Perseus raised—and what do we find? Every particle in that misty path is a mighty sun, suspended amidst multitudes of other mighty suns, massed in one long strip of splendor across the sky. ”

“ If there were no other celestial bodies of very low temperature and very large dimensions which absorbed the heat of the bright suns, the dark celestial bodies, the meteorites, and the dark cosmical dust would soon be so strongly heated by solar radiation that they would themselves turn incandescent, and the whole dome of the sky would appear to us like one glowing vault whose hot radiation down to the earth would soon burn every living thing. ”

“ Our solar system has its dust atmosphere, although it is extremely thinly sown. Besides the large blocks of matter, the meteoric stones, meteoric dust is incessantly falling from space upon the earth. ”

“ The higher we rise above the earth, the darker becomes the color of the sky, until it hangs like a pall of unspeakable blackness. Why is this? Why is light not light? Why this absolute darkness among so many, many suns? It is simply lack of dust! There must be something to throw back and scatter the rays of light before it can be visible. Unless far up in stellar space there is dust, star-dust, a whirl of motes or stones to seize and throw back the light, then all must be very dark. ”

“ Without laying too much stress upon this particular number, we may fairly say that the meteors picked up by the earth every day are to be reckoned by millions, and since they come at all seasons of the year, we shall have to admit that the region through which the earth moves, instead of being empty space, is really a dust cloud, each individual particle of dust being a prospective meteor. ”

“ It thus forms a transparent rift, through which we see farther and command a view of more stars than through the intensified dust-clouds on either hand. This rift is the Milky Way. The dust thrown aside toward the poles of the Milky Way is the substance of the nebulæ which abound there. Ahead, where the front of the star-plough is clearing the way, the chaos is nearer at hand, and consequently there the rift subtends a broader angle, and is filled with primordial dust, which, having been annexed by the vanguard of the star-swarm, forms the nebulæ seen only in that part of the Milky Way. ”

“ It is not so difficult, after all, then, to believe that there are immense collections of shadowy gases and meteoric dust whose presence is only manifested when they intercept the light coming from shining bodies behind them. ”

“ It was evidently like the dust seen in mid-ocean from the Peak of Teneriffe—something present all the time, and a permanent ingredient in the earth's atmosphere. At our own great elevation the sky was of a remarkably deep violet, and it seemed at first as if no dust was present in this upper air, but in getting, just at noon, in the edge of the shadow of a range of cliffs which rose twelve hundred feet above us, the sky immediately took on a whitish hue. On scrutinizing this through the telescope, it was found to be due to myriads of the minutest dust-particles. ”

“ An internal explosion, a fatal rush into some dense nebula or swarm of meteors, a collision with another star, or an approach within a few million miles of another star, scatters, in part or whole, the solid or liquid globe in a cloud of cosmic dust. When the violent outrush is over, the dust is gathered together once more into a star. At first cold and attenuated, its temperature rises as the particles come together, and we have, after a time, an incandescent nucleus shining through a thin veil of gas—a nebulous star. ”

“ They become intensely heated by friction against the atmosphere just as a bullet will when fired from a gun—only to a greater extent owing to the greater velocity. They disintegrate into dust which floats in the air for a time, when more or less of it is precipitated upon the surface of the earth. Disintegrated meteors, or star dust, as they are sometimes called, are often brought down by the rain or snow. ”

“ Many and strange are the hypotheses which have from time to time been put forth. Some have held meteors to be the scattered remnants of an exploded planet, ‘battered by the shocks of doom.’ Other speculators have thought that this dust of space originated in ejections from volcanic vents when the volcanoes which stud the surface of our satellite were in energy. ”

“ The world-wide distribution of atmospheric dust is a remarkable phenomenon. As the blue colour of the sky is universal, the whole of the higher atmosphere must be pervaded by myriads of ultra-microscopical particles, which, by reflecting the blue rays only, give us not only the azure vault of heaven, but in combination [ 256] with the coarser dust of lower altitudes, diffused daylight, the grand forms and motions of the fleecy clouds, and the 'gentle rain from heaven' to refresh the parched earth and make it beautiful with foliage and flowers. ”

“ As they are as a rule entirely dissipated in the upper air, often at a height of from fifty to seventy miles, it follows that many tons of the finest pulverized and gaseous matter are shot into the earth’s atmosphere every twenty-four hours from outer space, so that here is an independent and constant supply of dust, which we may expect to find coming down from far above the highest clouds. ”

“ May we not assume that some of these various forms of work, which can not be done by meteoroids large enough for us to see them as they enter the air, are done by this finer impalpable cosmic dust? Yes, we make such an assumption. There exist, no doubt, multitudes of these minute particles traveling in space. But science asks not only for a true cause, but a sufficient cause. ”

“ We have so far dwelt on the effects which the particles expelled from the sun and the stars exert on distant celestial bodies. It may be asked whether this dust does not act upon our own earth. We have already recognized the peculiar luminescence which on clear nights is diffused over the sky as a consequence of electrical discharges of this straying dust. This leads to the question whether the magnificent polar lights, which according to modern views are also caused by electric discharges in the higher strata of the atmosphere, are not produced by dust which the sun sends to us. ”

“ The denser the original atmosphere, the more widely the gases will have extended outward from the star, and the more dust will have been caught or secreted by it. We have seen that the limb of the sun has a reddish light because of the quantities of dust in the solar atmosphere. ”

“ Falling meteoric dust, which now exists in original state only on the bottom of the oceans, will gradually cover the entire surface of the Earth with a mantle coloured brick-red through the influence of atmospheric oxygen. When the oxygen itself is used up, the meteoric dust will retain its original greyish-green hue and lend it to the funeral pall of the Earth. ”

“ This dust comes down to us in a tangible form—dust shed from the sky on the earth, and large masses, magnificent specimens of meteorites, which have fallen from the heavens at different times, some of them weighing tons. There are swarms of dust traveling through space, and their motion may be gigantic. From photographs taken of the stars and nebulae, we are entitled to conclude that the swarms of dust meet and interlace each other, becoming raised by friction and collision to a very high temperature, and giving rise to what looks like a star. ”

“ Such a dust cloud will be no longer attracted toward the sun, but will be driven away by its light. It will be like the comets' tails, which consist chiefly of dust, radiate from the nuclei, and are always turned away from the sun. ”

“ There are everywhere in space little meteoric masses of matter, from the weight of a grain to a ton, and from the density of gas to rock. The earth meets 7,500,000 little bodies every day—there is collision—the little meteoroid gives out its lightning sign of extinction, and, consumed in fervent heat, drops to the earth as gas or dust. If we add the number light enough to be seen by a telescope, they cannot be less than 400,000,000 a day. ”

“ From the facts that have been above stated it will be apparent to anyone that the number of these meteoric stones in the air is being constantly reduced by their constant collision with the atmosphere and consequent reduction to ashes or dust. Another conclusion is that the earth must be gradually, but imperceptibly perhaps, increasing in size on account of the constant settling upon its surface of meteoric dust. ”

“ In most cases all controlling attraction would be feebly felt. These clouds of cosmical dust would float practically poised in the midst of space, and would gradually grow by the continued accession of new matter. ”

“ The effect is chiefly to be ascribed to the absorption of the blue rays by the dust; but it may partly be explained on the assumption that the solar radiations render the dust incandescent, though its temperature may be lower than that of the photosphere, because the dust lies outside the sun, and that it will therefore emit a relatively reddish light. The more dust there is in a nebula, the redder will be its luminescence; and as the quantity of dust increases in general with the extension of the nebula, that star which is surrounded by wider rings of nebulæ will in general be more red ”

“ The fall of exceedingly minute mineral particles in the snow and rain in regions far away from dust and smoke has been accepted as evidence that a so-called 'cosmic dust' floats in our atmosphere. Some physicists believe that this dust is always falling everywhere, that the bulk of the earth is increased, and that the phenomenon known to astronomers as acceleration of the moon's motion is thereby accounted for. ”

“ How it comes that this infinitely fine dust, finer probably than anything we can imagine, becomes at last, in the celestial spaces, agglomerated into meteoric irons and stones with which the earth is being continually bombarded, is one of the most interesting questions in the domain of science. ”

“ It is the dust formed as they are consumed, which, slowly settling to earth, constitutes the cosmic particles to which reference has been made.
But whilst on almost any clear night some few meteors may be seen to flash across the sky, observation has revealed the fact, that in certain months of the year, and on certain dates in those months, shooting-stars are much more numerous than in other months and on ordinary nights. ”

“ There were more clankings—the jeep-bus sealing off from the rocket. Then the vehicle stirred. The landscape outside began to move.
They saw Lunar City as they approached it. It was five giant dust-heaps, from five hundred-odd feet in height down to three. There were airlocks at their bases and dust-covered tunnels connecting them, and radar-bowls about their sides. But they were dust-heaps. Which was completely reasonable. There is no air on the moon. By day the sun shines down with absolute ferocity. It heats everything as with a furnace-flame. ”

“ And these processes are not the same, for the dust of the day sky is heated by sunshine, as are also, to a greater or less extent, both the air and the earth beneath, while the dust in the night sky, as does everything else that is freely exposed, loses of the heat it possesses and cools through radiation to space. ”

“ This cooler and denser air sinks toward the desert surface. When it reaches the ground, the air is deflected forward and sweeps up surface debris in its turbulence as a dust storm.
Saltation moves small particles in the direction of the wind in a series of short hops or skips.
Crops, people, villages, and possibly even climates are affected by dust storms. Some dust storms are intercontinental, a few may circle the 33 globe, and occasionally they may engulf entire planets. When the Mariner 9 spacecraft arrived at Mars in 1971, the entire planet was enshrouded in global dust. ”

“ Passing the earth on their return they will increase the amount of dust-clouds careering round it; and these will be further increased by the action of the ultra-violet rays of the sunlight causing particles to shoot radially away from the earth when the negative charge of the upper atmosphere has reached a certain amount, which particles, although starting sunward, will be swept back to the earth with the oncoming streams. ”

“ It is only in the moment of their dissolution that we really learn anything about meteors, for these bodies are much too small to be seen before they enter our atmosphere. The débris arising from their destruction is wafted over the earth, and, settling down eventually upon its surface, goes to augment the accumulation of that humble domestic commodity which men call dust. This continual addition of material tends, of course, to increase the mass of the earth, though the effect thus produced will be on an exceedingly small scale. ”