Astronomyby Titus Lucretius Carus
Let us sing what is the cause of the motions of the stars?
First of all, if the great globe of the sky turns round. The air presses on the pole at either end, and holds it outside and closes it in at both ends;
Then another current of air flows above
- If the whole sky moves round, it must be driven either by a current above or by a current below. straining on to the same goal, towards which the twinkling stars of the everlasting world roll on; or else that there is another current beneath, to drive up the sphere reversely, as we see streams moving round wheels with their scoops. It may be also that the whole sky can abide in its place, while yet the shining signs are carried on; either because swift currents of ether are shut within them, and seeking a way out are turned round and round,2. If the sky remains firm, the stars are moved either (a) by fireinside them or (b) by exterior currents, or (c) by desire to reach their proper fuel. All these causes act somewhere in the universe. and so roll on the fires this way and that through the nightly quarters of the sky; or else an air streaming from some other quarter without turns and drives the fires; or else they can themselves creep on, whither its own food invites and summons each as they move on, feeding their flaming bodies everywhere throughout the sky.
It is hard to declare for certain which of these causes it is in this world; but what can happen and does happen through the universe in the diverse worlds, fashioned on diverse plans, that is what I teach, and go on to set forth many causes for the motions of the stars, which may exist throughout the universe;
Of these it must needs be one which in our world too gives strength to the motions of the heavenly signs; but to affirm which of them it is, is in no wise the task of one treading forward step by step.
The earth is supported by a ‘second nature’ beneath it, which is closely connected with the air.Now that the earth may rest quiet in the mid region of the world, it is natural that its mass should gradually thin out and grow less, and that it should have another nature underneath from the beginning of its being, linked and closely bound in one with those airy parts of the world amid which it had its place and life. For this cause it is no burden, nor does it weigh down the air; even as for every man his own limbs are no weight, nor is the head a burden to the neck, nay nor do we feel that the whole weight of the body is resting on the feet;
our limbs are no weight to us because of their close connexion; but all weights which come from without and are laid upon us, hurt us, though often they are many times smaller. Of such great matter is it, what is the power of each thing. So then the earth is not suddenly brought in as some alien body, nor cast from elsewhere on alien air, but it has been begotten along with it from the first beginning of the world, a determined part of it, as our limbs are seen to be of us.
the earth shows its connexion with air above by communicating to it its own shocks; Moreover, the earth, when shaken suddenly by violent thunder, shakes with its motion all that is above it; which it could not by any means do, were it not bound up with the airy parts of the world and with the sky. For they cling one to the other with common roots, linked and closely bound in one from the beginning of their being. Do you not see too how great is the weight of our body, which the force of the soul, though exceeding fine, supports, just because it is so nearly linked and closely bound in one with it?
the soul, thanks to its close connexion, can lift the body. And again, what can lift the body in a nimble leap save the force of the soul, which steers the limbs? Do you not see now how great can be the power of a fine nature, when it is linked with a heavy body, even as the air is linked with earth, and the force of the mind with us?
The sun is not much larger or smaller than we see it. For fires, so long as seen and felt, do not look smaller.Nor can the sun’s blazing wheel be much greater or less, than it is seen to be by our senses. For from whatsoever distances fires can throw us their light and breathe their warm heat upon our limbs, they lose nothing of the body of their flames because of the interspaces, their fire is no whit shrunken to the sight. Even so, since the heat of the sun and the light he sheds, arrive at our senses and cheer the spots on which they fall, the form and bulk of the sun as well must needs be seen truly from earth, so that you could alter it almost nothing to greater or less. The moon, too,The moon is just the size we see it. whether she illumines places with a borrowed light as she moves along, or throws out her own rays from her own body, however that may be, moves on with a shape no whit greater than seems that shape, with which we perceive her with our eyes.For as long as things are clear in outline, they do not look smaller. For all things which we behold far sundered from us through much air, are seen to grow confused in shape, ere their outline is lessened. Wherefore it must needs be that the moon, inasmuch as she shows a clear-marked shape and an outline well defined, is seen by us from earth in the heights, just as she is, clear-cut all along her outer edges, and just the size she is. Lastly,The stars may be slightly smaller or larger than we see them. all the fires of heaven that you see from earth; inasmuch as all fires that we see on earth, so long as their twinkling light is clear, so long as their blaze is perceived, are seen to change their size only in some very small degree from time to time to greater or less, the further they are away: so we may know that the heavenly fires can only be a very minute degree smaller or larger by a little tiny piece.
The great light and heat of this small sun may be caused (a) because it is the one fountain-head of all the world’s light;This, too, is not wonderful, how the sun, small as it is, can send out so great light, to fill seas and all lands and sky with its flood, and to bathe all things in its warm heat. For it may be that from this spot the one well of light for the whole world is opened up and teems with bounteous stream, and shoots out its rays, because the particles of heat from all the world gather together on every side, and their meeting mass flows together in such wise, that here from a single fountain-head their blazing light streams forth. Do you not see too how widely a tiny spring of water sometimes moistens the fields, and floods out over the plains?(b) because it kindles the surrounding air;
Or again, it may be that from the sun’s fire, though it be not great, blazing light seizes on the air with its burning heat, if by chance there is air ready to hand and rightly suited to be kindled when smitten by tiny rays of heat; even as sometimes we see crops or straw caught in widespread fire from one single spark.(c) because it has hidden heat all around it. Perhaps, too, the sun, shining on high with its rosy torch, has at his command much fire with hidden heat all around him, fire which is never marked by any radiance, so that it is only laden with heat and increases the stroke of the sun’s rays.
The orbits of sun, moon, and stars may be causedNor is there any single and straightforward account of the sun, to show how from the summer regions he draws near the winter turning-point of Capricorn, and how turning back thence, he betakes himself to the solstice-goal of Cancer; and how the moon is seen in single months to traverse that course, on which the sun spends the period of a year as he runs.(a) because the nearer a heavenly body is to earth, the more slowly is it moved by the whirl of heaven. The sun then moves less swiftly than the stars, the moon than the sun, Therefore the moon seems to move quickest in the opposite direction: (b) because there are transverse currents which blow the sun from one tropic to the other: and so with moon and stars. There is not, I say, any single cause assigned for these things. For, first and foremost, it is clear that it may come to pass, as the judgement of the holy man, Democritus, sets before us, that the nearer the several stars are to earth, the less can they be borne on with the whirl of heaven. For its swift keen strength passes away and is lessened beneath, and so little by little the sun is left behind with the hindmost signs, because it is much lower than the burning signs. And even more the moon: the lower her course, the further it is from the sky and nearer to earth, the less can she strain on her course level with the signs. Moreover the weaker the whirl with which she is borne along, being lower than the sun, the more do all the signs catch her up all around and pass her. Therefore, it comes to pass that she seems to turn back more speedily to each several sign, because the signs come back to her. It may be too that from quarters of the world athwart his path two airs may stream alternately, each at a fixed season, one such as to push the sun away from the summer signs right to the winter turning-places and their icy frost, and the other to hurl him back from the icy shades of cold right to the heat-laden quarters and the burning signs.
Similarly, we must think that the moon and those stars which roll through the great years in great orbits, can be moved by airs from the opposite quarters in turn. Do you not see how by contrary winds the lower clouds too are moved in directions contrary to those above? Why should those stars be less able to be borne on by currents contrary one to the other through the great orbits in the heaven?
Night is caused either (a) because the sun’s light is extinguished or (b) because he travels under the earth. Dawn is caused either (a) because the returning sun sends his rays in advance or (b) because the fires which compose the new sun gradually collect. Such regular recurrence is not wonderful. It has many parallels in nature.But night shrouds the earth in thick darkness, either when after his long journey the sun has trodden the farthest parts of heaven, and fainting has breathed out his fires shaken by the journey and made weak by much air, or because the same force, which carried on his orb above the earth, constrains him to turn his course back beneath the earth.
Likewise at a fixed time Matuta sends abroad the rosy dawn through the coasts of heaven, and spreads the light, either because the same sun, returning again beneath the earth, seizes the sky in advance with his rays, fain to kindle it, or because the fires come together and many seeds of heat are wont to stream together at a fixed time, which each day cause the light of a new sun to come to birth. Even so story tells that from the high mountains of Ida scattered fires are seen as the light rises, and then they gather as if into a single ball, and make up the orb. Nor again ought this to be cause of wonder herein, that these seeds of fire can stream together at so fixed a time and renew the brightness of the sun. For we see many events, which come to pass at a fixed time in all things. Trees blossom at a fixed time, and at a fixed time lose their flower. Even so at a fixed time age bids the teeth fall, and the hairless youth grow hairy with soft down and let a soft beard flow alike from either cheek. Lastly, thunder, snow, rains, clouds, winds come to pass at seasons of the year more or less fixed.Where causes are original, effects come in due sequence. The disproportion of night and day, except at the equinox, may be caused either (a) because at that time the arcs of day and night into which the sun divides his daily revolution are necessarily equalized; For since the first-beginnings of causes were ever thus and things have so fallen out from the first outset of the world, one after the other they come round even now in fixed order.
And likewise it may be that days grow longer and nights wane, and again daylight grows less, when nights take increase; either because the same sun, as he fulfils his course in unequal arcs below the earth and above, parts the coasts of heaven, and divides his circuit into unequal portions; and whatever he has taken away from the one part, so much the more he replaces, as he goes round, in the part opposite it, until he arrives at that sign in the sky, where the node of the year makes the shades of night equal to the daylight. For in the mid-course of the blast of the north wind and of the south wind, the sky holds his turning-points apart at a distance then made equal, on account of the position of the whole starry orbit, in which the sun covers the space of a year in his winding course, as he lights earth and heaven with his slanting rays: as is shown by the plans of those who have marked out all the quarters of the sky, adorned with their signs in due order. Or else,or (b) because, at some seasons, the sun is delayed by dense air; or (c) because his fires gather together more slowly. because the air is thicker in certain regions, and therefore the trembling ray of his fire is delayed beneath the earth, nor can it easily pierce through and burst out to its rising. Therefore in winter time the long nights lag on, until the radiant ensign of day comes forth. Or else again, because in the same way in alternate parts of the year the fires, which cause the sun to rise from a fixed quarter, are wont to stream together now more slowly, now more quickly, therefore it is that those seem to speak the truth .
The phases of the moon may be caused, (a) if the moon shines by reflected light, by her gradual movement to and from a position opposite the sun.The moon may shine when struck by the sun’s rays, and day by day turn that light more straightly to our sight, the more she retires from the sun’s orb, until opposite him she has glowed with quite full light and, as she rises, towering on high, has seen his setting; then little by little she must needs retire back again, and, as it were, hide her light, the nearer she glides now to the sun’s fire from the opposite quarter through the orbit of the signs; as those have it, who picture that the moon is like a ball, and keeps to the path of her course below the sun. There is also a way by which she can roll on with her own light, and yet show changing phases of brightness.(b) If she shines by her own light: For there may be another body, which is borne on and glides together with her, in every way obstructing and obscuring her; yet it cannot be seen, because it is borne on without light.1. by another opaque body which accompanies and hides her; Or she may turn round, just like, if it so chance, the sphere of a ball, tinged over half its surface with gleaming light, and so by turning round the sphere produce changing phases, until she turns to our sight and open eyes that side, whichever it be, that is endowed with fires; and then little by little she twists back again and carries away from us the light-giving part of the round mass of the ball;2. because she has one light side, which she turns towards us and away again. as the Babylonian teaching of the Chaldaeans, n denying the science of the astronomers, essays to prove in opposition; just as if what each of them fights for may not be the truth, or there were any cause why you should venture to adopt the one less than the other. Or again, why a fresh moon could not be created every day with fixed succession of phases and fixed shapes, so that each several day the moon created would pass away,(c) If a fresh moon is created daily, by a regular succession of forms, like the succession of the seasons. and another be supplied in its room and place, it is difficult to teach by reasoning or prove by words, since so many things can be created in fixed order. Spring goes on her way n and Venus, and before them treads Venus’s winged harbinger; and following close on the steps of Zephyrus, mother Flora strews and fills all the way before them with glorious colours and scents. Next after follows parching heat, and as companion at her side dusty Ceres and the etesian blasts of the north winds. Then autumn advances, and step by step with her Euhius Euan. Then follow the other seasons and their winds, Volturnus, thundering on high, and the south wind, whose strength is the lightning. Last of all the year’s end brings snow, and winter renews numbing frost; it is followed by cold, with chattering teeth. Wherefore it is less wonderful if the moon is born at a fixed time, and again at a fixed time is blotted out, since so many things can come to pass at fixed times.
Eclipses of the sun may be caused (a) by the moon; (b) by some other opaque body; (c) when he passes through regions which choke his light. Eclipses of the moon may be caused (a) when earth gets between sun and moon; (b) and (c) as in the case of the sun.Likewise also the eclipses of the sun n and the hidings of the moon, you must think may be brought about by several causes. For why should the moon be able to shut out the earth from the sun’s light, and thrust her head high before him in the line of earth, throwing her dark orb before his glorious rays; and at the same time it should not be thought that another body could do this, which glides on ever without light. And besides, why should not the sun be able at a fixed time to faint and lose his fires, and again renew his light, when, in his journey through the air, he has passed by places hostile to his flames, which cause his fires to be put out and perish? And why should the earth be able in turn to rob the moon of light, and herself on high to keep the sun hidden beneath, while the moon in her monthly journey glides through the sharp-drawn shadows of the cone; and at the same time another body be unable to run beneath the moon or glide above the sun’s orb, to break off his rays and streaming light? And indeed, if the moon shines with her own light, why should she not be able to grow faint in a certain region of the world, while she passes out through spots unfriendly to her own light?