Dante and the early astronomers

by M. A. Orr

All these bodies are made, not of a mysterious ether, but of something just as wonderful, beautiful, and incomprehensible—the same stuff as Earth. Most probably all developed in long-past ages out of a nebula, or mass of gas which for some unknown reason was intensely hot. Small bodies, like the Moon and Mars, cooled off the most quickly, and have lost or are losing their air and their water; larger bodies, like Jupiter, have still some heat, and are probably in a more or less fluid condition. On the sun an inconceivable heat still rages; everything is in a gaseous state, and this globe which men used to think eternally changeless is the scene of the fiercest turmoil; currents are always ascending and descending, clouds of fire are flung up thousands of miles high, and patches which look black compared with the surrounding surface and indicate a mysterious commotion are constantly forming, developing, and disappearing. The sun is enormously larger than Dante thought, larger than all the planets put together, large enough for our moon’s whole orbit to fit comfortably inside. It is hot enough and brilliant enough to light all the planets: this, which was only a guess of mediæval astronomers, we know as a fact to-day, and the planets which are suitably placed show it to us, when seen in the telescope; Venus, for instance, changing her phase “according as the sun looks upon her,” exactly like the moon. And Earth must show similar phases as seen from Mars.

For Aristarchus was right: the sun is the centre of the planetary movements, including those of the planet Earth.

We saw how Ptolemy’s system hinted at this, in the significant connection between each planet’s movement and the movement of the sun; but a strong argument against it was that if Earth were really moving round the sun we ought to see a yearly displacement in the positions of all the stars. Modern instruments have at last made it possible to perceive this displacement. About a hundred stars, our nearest neighbours, describe a very minute orbit in the sky, which in every case is an exact reflection of the sun’s apparent orbit round the earth. Unless, therefore, we are going to provide all these stars, as well as the planets, with epicycles, which must all revolve in the same period, in the same direction, and in parallel planes, we must conclude that the movement is really Earth’s yearly movement round the sun. These miniature star-orbits also show us the stupendous distances which lie between Earth and the nearest stars, while by far the greater number are too remote to show any displacement at all.

Aristarchus and those other ancient astronomers were also right who thought that Earth was turning on her axis, and thus producing by her own motion the alternation of day and night, and the apparent circling of the stars. When we look now at stars hastening across the sky, they no longer present themselves to our thought as fixed on a sphere with a radius of 20,000 Earth-radii, which is revolving round us at a tremendous speed; we feel that we are looking into space at glowing globes which are at various and almost inconceivable distances from us; also that all those we see, all those that Hipparchus numbered, are but an insignificant fraction of all those now known to exist. All have their own real motions, as well as the apparent motions produced by Earth, but these are in different directions, towards what goal we cannot at present tell. Compared with them, Earth is indeed insignificant, in size and also in brightness, for while she shines with reflected light they glow as the sun does and are his peers.

Nevertheless, with them too we have a feeling of kinship, for analysis of their light shows that they too are made of earth-stuffs: they are not eternal nor changeless, for very many vary constantly in their light, and they are at different stages of development, some appearing very young, while others are beginning to burn dim and low, and some can only be inferred to exist, for they seem to be wholly dark.

More wonderful perhaps than anything else, we find that the force which binds the whole of our sun’s family together is nothing strange and unknown, but the same familiar force of gravity, which the Greeks knew so well but thought only applicable to Earth. Its rule includes the seemingly unruly comets and meteors, and it extends as far as our search can reach, to the uttermost star.

This sense of unity throughout the world, which is always growing stronger, is comforting. And we allow ourselves to wonder whether intelligent life has not developed elsewhere, as well as on this globe that we inhabit. Perhaps each planet that attends our sun is fitted at some period to be the abode of life: surely among the millions of stars many must have attendant planets, and on some of them even now are living, thinking, beings.

Dante’s world was easier to think about than ours. Encompassed by an infinity which gave the imagination free scope, the material universe within was neatly rounded off, as it were, complete, finished. Only in the central spot was any development taking place, and thither were directed all effects of the circling spheres. Our universe is vague, vast, mysterious, without known limits or centre, offering problem after problem to the thinker. Dante’s marvellous moon-substance is simple compared with the baffling nature of our æther; Dante’s Angel-Movers are intelligible compared with the amazing mystery of universal gravitation.

Yet when we lift our eyes from earth to heaven, we share the feeling of our mediæval forefathers, of the ancient Greeks, of the earliest men whenever and wherever they became men. The unerring courses of the stars speak to us, “the unperturbed to the perturbed,” of perfect harmony, untouched by chance or arbitary conflicting wills. Now, however, we do not believe this is because heaven is essentially different from earth: it is because we see there only the grand outlines, only the working of great laws, of a system which includes our own earth. Could we but lose sight of the details here, and view the history of man as we view the stars, the harmony would be as grand.

HYMN TO ZEUS.