CHAPTER XXXII.

THE DAWN OF ASTRONOMY.

The beginnings of astronomy lie in the distance of earliest historical ages. It is no easy matter to say when first, in all probability, this science grew into existence. Astronomy was alive before the British nation was heard of; before Saxons or Franks had sprung into being; before the Roman Empire extended its iron rule; before the Grecian Empire began to flourish; before the Persian Empire gained power; before the yet earlier Assyrian Empire held sway.

Among the ancient Chaldeans were devoted star-gazers--much more devoted than the ordinary run of educated Anglo-Saxons in this present century. They earnestly sought, in the dim light of those ages, to decipher the meaning of heaven’s countless lamps. We have better instruments, and more practiced modes of reasoning; also, we have the collected piles of knowledge built up by our forefathers through tens of centuries. Yet our search is in essence the same as was theirs, to know the truth about the stars: not merely to start some attractive theory, and then to prove that our theory must be right, because we have been so clever as to start it; but to discover that which is in those regions of space. No lower aim than this is worthy to be called scientific.

Mistakes, of course, are made; how should it be otherwise? A man finding his way at night, for the first time, through a wild and unknown country, will almost certainly take some wrong turns before he discovers the right road. In astronomy, as in all other natural sciences, blunders are a necessity if advance is to be made. We have to grope our way to knowledge through observation and conjecture; in simpler terms, through gazing and guessing. Observation of facts leads to conjecture as to the possible causes for those facts; and each conjecture is proved by later observation to be either right or wrong. If proved to be right, it takes its place among accepted truths; if proved to be wrong, it is flung aside. Some pet delusions die hard, because of people’s love for them.

Astronomy, as an infant science, mixed up with astrology, existed in the days when the Pyramids were juvenile, and when the Assyrian sculptures were modern. How much farther back who shall say? By astrology, those who studied the heavens endeavored to determine the fate of men and of nations, to predict events, and to interpret results. They paid particular attention to the aspect of the planets, and the general appearance of the firmament.

These observations were at first simple remarks made by the shepherds of the Himalayas after sunset and before sunrise: The phases of the moon, and diurnal retrograde motion of that body with reference to the sun and stars; the apparent motion of the starry sky accomplished silently above our heads; the movements of the beautiful planets through the constellations; the shooting star, which seems to fall from the heavens; eclipses of the sun and moon, mysterious subjects of terror; curious comets, which appear with disheveled hair in the heights of heaven,--such were the first subjects of these old observations made during thousands of years.

The ancient Chaldean star-gazers had rivals among the early Egyptians; and the Chinese profess to have kept actual record of eclipses during between three and four thousand years. The earlier records are not trustworthy; but of thirty-six eclipses reckoned by the Chinese sage, Confucius, no less than thirty-one have been proved true by modern astronomers.

We can not name with certainty those people whose shepherds first gazed with intelligent eyes upon the midnight sky, and noted the steady sweep of stars across the firmament--intelligent eyes, that is to say, so far as man then knew how to use his eyes intelligently; so far as man had begun to note anything in nature, to watch, to compare, and to conjecture causes.

In those times, and indeed for long afterwards, men thought much more about the “influences” of stars upon their own lives, and about supposed prophecies of the future to be read in the sky, than about the actual physical condition of the stars themselves, or the causes and meanings of the various phenomena observed in the heavens.

The desire to know, for the pure delight of knowing, had perhaps hardly begun to dawn upon the mind of man. What people did want to know was what might be going to happen to themselves; whether _they_ would be happy or unhappy; and the stars were chiefly of interest as appearing to tell beforehand of troubles or joys to come.

The wisest of men in those times knew less of the outspread heavens than many a child now knows in our public schools. Earth and sky were one vast bewildering puzzle. They had to discover everything for themselves--how the sun rose each morning and set each evening; how the seasons changed in steady sequence through the year; how the moon and stars journeyed in the night; how the ocean-tides went and came; how numberless every-day phenomena took place.

In olden days the daily rising and setting of the sun was a mystery, accounted for by divers theories, none of which were right; and the march of stars across the midnight sky was a complete puzzle; and an eclipse of sun or moon was a fearful perplexity; and the tides of ocean were a great bewilderment. These things are mysteries still to barbarous nations; but they perplex us no longer, because we have found out the mode in which such movements, or appearances of movement, are brought about through the action of quite natural causes.

As a first step, in earliest times, the journey of the sun by day, the journeys of moon and stars by night, across the sky, could hardly fail to arrest attention. Very early, too, the stars were grouped into constellations, definite figures and names being attached to each. Many of the constellations are now known to us by names which belong to the earliest historic ages.

The stars were known as “fixed,” because they continued unchangeably in their relative positions--that is, in the position held by each star with respect to its neighbor stars--although the whole array of them moved nightly in company; constellations rising and setting at night, as the sun rose and set in the day.

Ages may well have passed before the planets were recognized as distinct from the fixed stars; ages more before any definite plan was noted in their wanderings. In the course of time men’s attention was directed to these matters; and one fact after another, of daily or monthly or yearly occurrence, was observed, and commented upon, and became familiar to the minds of people. Very slowly the first beginnings of systematized knowledge took shape and grew, one discovery being made after another, one explanation being offered after another, one theory being started after another.

But an essential difference existed between the infantine science of those primitive days and the matured astronomy of these later days. The whole ancient science was built upon a huge mistake. Men held, as a fact of absolutely unquestionable certainty, that this earth of ours--this small whirling globe, less than eight thousand miles in diameter--was the center, around which sun, moon, and stars all revolved.

The Greek philosopher Thales, who lived about six hundred years before Christ, is said to have laid the foundations of the Grecian astronomy; and Pythagoras is stated to have been one of his disciples. Though, in many respects, Thales wandered wide of the truth, he yet taught many correct ideas; as, for instance, that the stars were made of fire; that the moon had all her light from the sun; that the earth was a sphere in shape, besides other facts respecting the earth’s zones and the sun’s apparent path in the sky. He was also one of the three ancient astronomers who were able to calculate and foretell eclipses.

After him came numerous astronomers, of greater or less merit, in the Grecian and in other schools. They watched carefully; they discovered many things of interest; they held divers theories. But one truth never took firm root among them, although several of them dimly apprehended it; and this was the very foundation-truth, for lack of which they were all going hopelessly astray--the simple truth that our earth is _not_ the center of the universe, and that our earth _does_ move. Yet it is not surprising. No wonder they were slow to grasp such a possibility.

Anything more bewildering to the mind of ancient man than the thought of a solid, substantial world floating in empty space, supported upon nothing, upheld by nothing, can hardly be imagined. As yet little was known of the controlling laws or forces of nature, and that little was with reference only to our earth. The very suspicion of gravitation as a universal law lay in the far-distant future, waiting for the intellect of a Newton to call it out of apparent chaos; and the delicate balance of forces, by means of which the Solar System may almost be said to exist, could not be so much as guessed at.

So men still clung to the thought of earth as the center of all things, and still believed in a little sun, busily circling round her once in every twenty-four hours.

Perhaps the greatest of all ancient astronomers was Hipparchus, about 150 B. C., who did more than any other in those early times to gather together the scattered facts of astronomy, and to arrange them into one united and orderly whole. He it was who discovered the precession of the equinoxes. He studied eclipses and the motions of the various planets. He made elaborate and valuable astronomical tables and star-catalogues; but he, like others, failed to discover the gigantic error which lay at the root of the whole ancient science.

Despite this great mistake, still persistently believed in, and despite the crude notions of early astronomers on many points, it is marvelous how much they did manage to observe and to learn for themselves,--as to the sun and his apparent path, as to the moon and her path, as to the five then known planets and their paths, as to eclipses and other phenomena.

By all such careful watching, although they to some extent missed their aim and fell into mistakes, yet they paved a way to later discoveries and to fuller knowledge. Their work was not thrown away, their trouble was not lost; for out of their very errors grew the fair form of truth.

Nearly three hundred years after the time of Hipparchus came the famous Ptolemy--famous, not, like certain other astronomers, for stupendous genius, or for the brilliancy and accuracy of his observations, but rather noted for the ingenuity of his explanations, and for the adroit manner in which he systematized such knowledge, on the subject of the heavenly bodies, as was then in the possession of mankind.

Ptolemy’s name is best known in connection with what is commonly called “The Ptolemaic System of the Universe,” and his greatest astronomical work is best known as the _Almagest_.

A great many of Ptolemy’s leading notions, as well as the principal mass of facts upon which he worked, were doubtless borrowed from Hipparchus. The latter is said to have explained the movements of the sun and of the moon by means of small epicycles, traveling round the earth on circular orbits; and even Hipparchus did not originate this fundamental idea of the so-called “Ptolemaic System,” which had indeed been held by the ancients in much earlier days. Hipparchus worked it out to some extent, and Ptolemy carried on the process much farther, giving forth the system to the world in such wise that ever since it has gone by his name.

The theory of cycles and epicycles lasted long--lasted from the time of Ptolemy in the second century to the time of Copernicus in the sixteenth century, of whom we have already spoken.

[For about two thousand years, astronomers observed attentively the apparent revolutions of the heavenly bodies, and this attentive study gradually showed them a large number of irregularities and inexplicable complications, until at last they recognized that they were deceived as to the earth’s position, in the same way that they had been deceived as to its stability. The immortal Copernicus, in particular, discussed with perseverance the earth’s motion, already previously suspected for two thousand years, but always rejected by man’s self-love; and when this learned Polish canon bid adieu to our world in the year 1543, he bequeathed to science his great work, which demonstrated clearly the long-standing error of mankind.--_F._]

The new theory of Copernicus had to make its way slowly against the dead weight of unreasoning public opinion, and against wrongly-reasoning hierarchical opposition. In time, gradually, despite all resistance, the truth made its way, and was generally received, though not till Galileo had been forced by ecclesiastical authority to recant his opinions. All the same, Copernicus, Kepler, Galileo, were right; public sentiment and the Church were wrong,--the earth did move, and was not the fixed universe center, and, by and by, those who lived on earth had to acknowledge the same.

The succession of these great men is interesting to note. Between the two shining lights, Hipparchus and Ptolemy, nearly three hundred years intervened. But as the history of the world advances, we find brilliant scientific minds appearing more quickly, one following close upon another, instead of their being divided by long intervals of blankness.

Within thirty years from the death of Copernicus, were born two mighty men of Science: Kepler, who lived till 1630; and Galileo, who lived till 1642, when England was plunged in civil strife.

Between Copernicus and Kepler came Tycho Brahe. Copernicus was a Roman ecclesiastic, born in Poland. Tycho Brahe was a wealthy Danish nobleman, an ardent lover of astronomy, and a most patient and accurate observer. But Tycho held fast by the old astronomy. He was not convinced by the arguments of Copernicus. To him, earth was still the motionless center of all things. He was willing to allow that the rest of the planets circled round the sun, as an explanation of things which he could not help seeing; but the sun itself had still, in Tycho’s imagination, to revolve daily, with planets and stars and the whole sky, round our earth.

As an explainer of causes, therefore, Tycho rose to no lofty heights. The real good which he did was in watching and noting actual phenomena, not in trying to explain how those phenomena were brought about. This was left for one of his young pupils, a sickly German lad, named John Kepler.

In later years, Kepler made a grand use of his master’s mass of careful and thoroughly dependable observations. These had really been gathered together by Tycho, with a view of disproving the Copernican theory, and of establishing the main features of the olden astronomy, with certain improvements. But Kepler used the accumulated information to disprove the old astronomy, and to establish the truth of the new Copernican system which Tycho had rejected. He found a vast advantage, ready to his hand, in the collection of careful observations systematically worked out by Tycho in his observatory during many a long year. And Kepler did not fail to use his advantage.

The planets still refused, as they always had refused, to keep to the paths marked out for them by astronomers. Kepler grappled with the difficulty. He particularly turned his attention to Mars, that near neighbor of ours, in which we are all now so much interested. A long series of close observations of Mars’s movements, made by Tycho in the course of many years, lay before him; and he knew that he could depend upon the absolute honesty and accuracy of Tycho’s work.

With immense labor and immense patience, he went into the matter, still clinging to the old idea of a circular pathway round the sun. He tried things this way and that way. He placed his orbit in imagination after one mode and another mode; he conjectured various arrangements; he tested and proved them in turn, comparing each plan with observations made,--and still Mars defied all his efforts; still the little world went persistently wrong, traveling contrary to every theory.

Thus far, nobody had ever thought of an orbit of any other shape than a circle. When a straightforward journey round a circle was found impossible, then epicycles were introduced to explain the planet’s perplexing motions. No one had dreamt of an elliptic pathway. But suddenly a gleam of daylight came upon this groping in the dark. What if Mars traveled round the sun--_not_ in a circle, but in an oval?

Kepler tried this oval and that oval, comparing observations past--testing, examining, proving or disproving, with unwearied patience. And at length he found, beyond dispute, that Mars actually did travel round the sun in a yearly pathway, which was shaped, not as a circle, but as the kind of oval known as an _ellipse_; and, further, that the sun was not in the exact center of this ellipse, but to one side of the center, in one of the foci. Kepler’s success in detecting the true shape of a planetary orbit is doubtless owing to the fact that the orbit of Mars makes a wider departure from the circular form than any of the other important planets.

One step further would have led Kepler to the knowledge that comets also travel in elliptic orbits--only in very long and narrow ones generally. But he had quite made up his mind that all comets merely paid our sun one visit, and never by any chance returned; so he did not trouble himself to enter into calculations with respect to them. This taking for granted of ideas long held was a very common practice in those days.

The above wonderful discovery of elliptic orbits, in place of circular orbits, was only one among many made by the illustrious Kepler--discoveries not carelessly hit upon, as one might pick up in the street a valuable stone which somebody had dropped, but earnestly sought for, and found with toil and diligence, as gems are first found in foreign lands, after much seeking and long patience. Casual discoveries in science are rare. Attainment is far more usually made through intense study, through hard work, through profound thought, through a gradual groping upward out of darkness to the point where daylight breaks forth.

The three well-known “Laws of Kepler” still lie at the very foundation of the modern system of astronomy. They are: First, every planet moves in an elliptical orbit, in one focus of which the sun is situated; second, the line drawn from the sun to a planet moves over equal areas in equal times; and, third, the square of the periodic times of the planets varies inversely as the cubes of their distances.