Tycho Brahe' System of Astronomy

Tycho Brache was the great restorer and advancer of Astronomy.

• He spent his life and wasted his fortune on it.
• His observations were both more numerous and more accurate than those of all the astronomers who had gone before him.
  • He himself was so much affected by objections to the point that he could not embrace the system of Copernicus

He admired Copernicus and all his astronomical observations tended to confirm his system. They demonstrated, that:

• Venus and Mercury were sometimes above, and sometimes below the Sun
• consequently, the Sun, and not the Earth, was the center of their periodical revolutions
• Mars, when in his meridian at midnight, was nearer to the Earth than the Earth is to the Sun; though, when in conjunction with the Sun, he was much more remote from the Earth than that luminary

These were absolutely inconsistent with the system of Ptolemy. Copernicus’ system proved that:

• the Sun, and not the Earth, was the center of the periodical revolutions of Mars, Venus, and Mercury
• the Earth was placed between the orbits of Mars and Venus.
• the same thing was probable with regard to Jupiter and Saturn

• Comets were superior to the Moon, and moved through the heavens in all possible directions
  • This was incompatible with the Solid Spheres of Aristotle and Purbach, and the established Astronomy.

All these observations, joined to his aversion to the system, and perhaps, notwithstanding the generosity of his character, some little jealousy of the fame of in which the Earth Copernicus, suggested to Tycho the idea of a new hypothesis, continued to be, as in the old account, the immoveable center of the universe, round which the firmament revolved every day from east to west, and, by some secret virtue, carried the Sun, the Moon, and the Five Planets along with it, notwithstanding their immense distance, and notwithstanding that there was nothing betwixt it and them but the most fluid ether.

But, although all these seven bodies thus obeyed the diurnal revolution of the Firmament, they had each of them, as in the old system, too, a contrary periodical eastward revolution of their own, which made them appear to be every day, more or less, left behind by the Firmament.

The Sun was the center of the periodical revolutions of the 5 Planets; the Earth, that of the Sun and Moon.

The 5 Planets followed the Sun in his periodical revolution round the Earth, as they did the Firmament in its diurnal rotation. The three superior Planets comprehended the Earth within the orbit in which they revolved round the Sun, and had each of them an Epicycle to connect together, in the same manner as in the system of Ptolemy, their direct, retrograde, and stationary appearances.

As, notwithstanding their immense distance, they followed the Sun in his periodical revolution round the Earth, keeping always at an equal distance from him, they were necessarily brought much nearer to the Earth when in opposition to the Sun, than when in conjunction with him. Mars, the nearest of them, when in his meridian at midnight, came within the orbit which the Sun described round the Earth, and consequently was then nearer to the Earth than the Earth was to the Sun. The appearances of the two inferior Planets were explained, in the same manner, as in the system of Copernicus, and consequently required no Epicycle to connect them.

The circles in which the Five Planets performed their periodical revolutions round the Sun, as well as those in which the Sun and Moon performed theirs round the Earth, were, as both in the old and new hypothesis, Eccentric Circles, to connect together their differently accelerated and retarded motions.

Such was the system of Tycho Brache, compounded, as is evident, out of these of Ptolemy and Copernicus; happier than that of Ptolemy, in the account which it gives of the motions of the two inferior Planets; more complex, by supposing the different revolutions of all the Five to be performed round two different centers; the diurnal round the Earth, the periodical round the Sun;

But, in every respect, more complex and more incoherent than that of Copernicus. Such, however, was the difficulty that mankind felt in conceiving the motion of the Earth, that it long balanced the reputation of that otherwise more beautiful system.

Those who considered the heavens only, favoured the system of Copernicus, which connected so happily all the appearances which presented themselves there. But that those who looked upon the Earth, adopted the account of Tycho Brache, which, leaving it at rest in the center of the universe, did less violence to the usual habits of the imagination.

The learned were, indeed, sensible of the intricacy, and of the many incoherences of that system; that it gave no account why the Sun, Moon, and Five Planets, should follow the revolution of the Firmament; or why the Five Planets, notwithstanding the immense distance of the 3 superior ones, should obey the periodical motion of the Sun; or why the earth, though placed between the orbits of Mars and Venus, should remain immoveable in the center of the Firmament, and constantly resist the influence of whatever it was, which carried bodies that were so much larger than itself, and that were placed on all sides of it, periodically round the Sun. Tycho Brahe died before he had fully explained his system.

His great and merited renown disposed many of the learned to believe, that, had his life been longer, he would have connected together many of these incoherences, and knew methods of adapting his system to some other appearances, with which none of his followers could connect it.

The objection to the system of Copernicus, which was drawn from the nature of motion, and that was most insisted on by Tycho Brahe, was at last fully answered by Galileo; not, however, till about thirty years after the death of Tycho, and about a hundred after that of Copernicus. It was then that Galileo, by explaining the nature of the composition of motion, by showing, both from reason and experience, that a ball dropt from the mast of a ship under sail would fall precisely at the foot of the mast, and by rendering this doctrine, from a great number of other instances, quite familiar to the imagination, took off, perhaps, the principal objection which had been made to this hypothesis.

Several other astronomical difficulties, which encumbered this account of things, were removed by the same philosopher. Copernicus, after altering the center of the world, and making the Earth, and all the Planets revolve round the Sun, was obliged to leave the Moon to revolve round the Earth as before. But no example of any such secondary Planet having then been discovered in the heavens, there seemed still to be this irregularity remaining in the system. Galileo, who first applied telescopes to discovered, by their assistance, the Satellites of Jupiter, which, revolving Astronomy, round that Planet, at the same time that they were carried along with it in its revolution, round either the Earth, or the Sun, made it seem less contrary to the analogy of nature, that the Moon should both revolve round the Earth, and accompany her in her revolution round the Sun.

It had been objected to Copernicus, that, if Venus and Mercury revolved round the Sun, in an orbit comprehended within the orbit of the Earth, they would show all the same phases with the Moon, present, sometimes their darkened, and sometimes their enlightened sides to the Earth, and sometimes part of the one, and part of the other. He answered, that they undoubtedly did all this; but that their smallness and distance hindered us from perceiving it. This very bold assertion of Copernicus was confirmed by

His telescopes rendered the phases of Venus quite sensible, and thus Galileo.

demonstrated, more evidently than had been done, even by the observations of Tycho Brahe, the revolutions of these two Planets round the Sun, as well as so far destroyed the system of Ptolemy.

The mountains and seas, which, by the help of the same instrument, he discovered, or imagined he had discovered in the Moon, rendering that Planet, in every respect, similar to the Earth, made it seem less contrary to the analogy of nature, that, as the Moon revolved round the Earth, the Earth should revolve round the Sun.

The spots which, in the same manner, he discovered in the Sun, demonstrating, by their motion, the revolution of the Sun round his axis, made it seem less improbable that the Earth, a body so much smaller than the Sun, should revolve round her axis in the same manner.

Succeeding telescopical observations, discovered, in each of the Five Planets, spots not unlike those which Galileo had observed in the Moon, and thereby seemed to demonstrate what Copernicus had only conjectured, that the Planets were naturally opaque, enlightened only by the rays of the Sun, habitable, diversified by seas and mountains, and, in every respect, bodies of the same kind with the Earth; and thus added one other probability to this system. By discovering, too, that each of the Planets revolved round its own axis, at the same time that it was carried round either the Earth or the Sun, they made it seem quite agreeable to the analogy of nature, that the Earth, which, in every other respect, resembled the Planets, should, like them too, revolve round its own axis, and at the same time perform its periodical motion round the Sun.