Astronomy Books

"As for the past Discourses, and particulatly in this last, of the reason of the Ebbing and Flowing of the Sea, I do not, to speak the truth, very well apprehend the same, but by that slight Idea, what e­ver it be, that I have formed thereof to my self, I confesse that your conceit seemeth to me far more ingenuous than any of all those that I ever heard besides, but yet neverthelesse I esteem it not true and concluding: but keeping alwayes before the eyes of my mind a solid Doctrine... I know that both you being asked, Whether God, by his infinite Power and Wisdome might confer upon the Element of Water the reciprocal motion which we observe in the same in any other way, than by making the containing Vessel to move; I know, I say, that you will answer, that he might, and knew how to have done the same many wayes, and those unimaginable to our shallow understanding: upon which I forthwith conclude, that this being granted, it would be an extravagant boldnesse for any one to goe about to limit and confine the Divine Power and Wisdome to some one particular conjecture of his own."

"This of yours is admirable, and truly Angelical Do­ctrine, to which very exactly that other accords, in like manner divine, which whilst it giveth us leave to dispute, touching the constitution of the World, addeth withall (perhaps to the end, that the exercise of the minds of men might neither be discou­raged, nor made bold) that we cannot find out the works made by his hands. Let therefore the Disquisition permitted and or­dain'd us by God, assist us in the knowing, and so much more admiring his greatnesse, by how much lesse we finde our selves too dull to penetrate the profound Abysses of his infinite Wis­dome."

"Above all, I shall very impatiently wait to hear the Elements of the new Science of our Academick about the natural and violent local Motions. And in the mean time, we may, according to our custome, spend an hour in taking the Air in the Gondola that waiteth for us. FINIS."

"Judicious Reader, There was published some years since in Rome a salutiferous edict which... imposed a seaonable silence upon the Pythagorean opinion of the mobility of the earth. ...that decree was not the production of sober scrutiny but of ill-informed passion... consultors altogether ignorant of astronomical observations ought not to clip the wings of speculative wits with rash prohibitions."

"I thought fit... to appear openly upon the theatre of the World as a witness of the naked truth."

"It is my resolution... to give foreign nations to see of this matter... And, collecting all the speculations of mine that concern the Copernican system, to let them know that... there proceed from this climate not only doctrines for the health of the soul but also ingenious discoveries for the delight of the mind."

"I have personated the Copernican... proceeding upon the hypothesis purely mathematical; striving by every artifice to represent it superior not to that of the immobility of the Earth absolutely but as it is defended by some who, claiming to profess the Peripatetic doctrine, retain of it no more than the name, and are content, foregoing the old ways, to adore shadows, not philosophizing with their own intelligence but with the sole remembrance of a few principles badly understood."

"I will endeavour to show that all experiments that can be made upon the Earth are insufficient means to conclude for its mobility but are indifferently applicable to the Earth, movable or immovable..."

"We will examine the celestial phenomena that make for the Copernican hypothesis, as if it were to prove absolutely victorious, adding by the way certain new observations which yet serve only for astronomical facility, not for natural necessity."

"I will propose an ingenious fancy. ...the unknown problem of the tides might receive some light, admitting of the Earth's motion. ...I have thought good to lay down those probabilities that would render it credible, admitting that the Earth did move."

"I hope that by these considerations the world will come to know that, if other nations have navigated more than we, we have not studied less than they; and that our returning to assert the Earth's stability and to take the contrary only for a mathematical fantasy, proceeds not from lack of acquaintance with others' ideas thereof but... from those reasons that piety, religion, the knowledge of the Divine Omnipotence, and a consciousness of the incapacity of man's understanding dictate to us."

"I chanced, many years ago, as I lived in the stupendous city of Venice, to converse frequently with the Signor Giovan Francesco Sagredo, a man of noble extraction and most acute intellect. There came thither from Florence, at the same time, Signor Filippo Salviati, whose least glory was the eminence of his blood and magnificence of his estate, a sublime intellect that knew no more exquisite pleasure than elevated speculations. In the company of these two I often discoursed of these matters before a certain Peripatetic philosopher, who seemed to have no greater obstacle in understanding the truth than the fame he had acquired by Aristotelian interpretations. Now, seeing that inexorable fate has deprived Venice and Florence of those two great lights in the early summer of their years, I did resolve... to perpetuate their lives to their honor in these leaves... Nor shall the honest Peripatetic want his place, to whom, for his excessive affection towards the commentaries of Simplicius, I thought fit, without mentioning his own name, to leave that of the author he so much respected. Let these two great souls, ever venerable to my heart, please to accept this public monument of my never dying love; and let the remembrance of their eloquence assist me in delivering to posterity the considerations that I have promised."

"There had casually taken place... several discourses at times between these gentlemen which had rather inflamed than satisfied in their minds the thirst they had for learning; whereupon they took the wise resolution to meet together for certain days in which, all other business set aside, they might betake themselves with more ordered speculation to contemplate the wonders of God in heaven and on earth."

"We have in our age new accidents and observations, and such, that I question not in the least, but if Aristotle were now alive, they would make him change his opinion; which may be easily collected from the very manner of his discoursing: For when he writeth that he e­steemeth the Heavens inalterable, &c. because no new thing was seen to be begot therein, or any old to be dissolved, he seems im­plicitely to hint unto us, that when he should see any such accident, he would hold the contrary; and confront, as indeed it is meet, sensible experiments to natural reason: for had he not made any reckoning of the senses, he would not then from the not seeing of any sensible mutation, have argued immutability."

"I do believe for certain, that he [Aristotle] first procured by help of the senses, such experiments and obser­vations as he could, to assure him as much as it was possible, of the conclusion, and that he afterwards sought out the means how to demonstrate it: For this, the usual course in demonstrative Sciences, and the reason thereof is, because when the conclusion is true, by help of resolutive Method, one may hit upon some pro­position before demonstrated, or come to some principle known per se; but if the conclusion be false, a man may proceed in in­finitum, and never meet with any truth already known; but ve­ry oft he shall meet with some impossibility or manifest absurdi­ty."

"Nor need you question but that Pythagoras a long time be­fore he found the demonstration for which he offered the Hecatomb, had been certain, that the square of the side subtending the right angle in a rectangle triangle, was equal to the square of the other two sides: and the certainty of the conclusion condu­ced not a little to the investigating of the demonstration, un­derstanding me alwayes to mean in demonstrative Sciences."

"Tycho wrote a little book [On the New Star or De nova stella] on the new star, maintaining that it had practically no parallax, and therefore could not be, as some supposed, a comet. Deeming authorship beneath the dignity of a noble he was very reluctant to publish, but he was convinced of the importance of increasing the number and accuracy of observations, though he was by no means free from all the erroneous ideas of his time. The little book contained a certain amount of astrology, but Tycho evidently did not regard this as of very great importance. He adopted the view that the very rarity of the phenomenon of a new star must prevent the formulation and adoption of definite rules for determining its significance."

"We gather from lectures which he was persuaded to deliver at the University of Copenhagen that, though in agreement with the accepted canons of astrology as to the influence of planetary conjunctions and such phenomena on the course of human events, he did not consider the fate predicted by anyone’s horoscope to be unavoidable, but thought the great value of astrology lay in the warnings derived from such computations, which should enable the believer to avoid threatened calamities."

"In 1575 he left Denmark once more and made his way to Cassel, where he found a kindred spirit in the studious Landgrave, William IV of Hesse, whose astronomical pursuits had been interrupted by his accession to the government of Hesse, in 1567. Tycho observed with him for some time, the two forming a firm friendship, and then visited successively Frankfort, Basle, and Venice, returning by way of Augsburg, Ratisbon, and Saalfeld to Wittenberg; on the way he acquired various astronomical manuscripts, made friends among practical astronomers, and examined new instruments."

"On his return to Denmark to fetch his family with the object of transferring them to Basle, he found that his friend the Landgrave had written to King Frederick on his behalf."

"Tycho accepted from the king a grant of the small island of Hveen, in the Sound, with a guaranteed income... Here Tycho built his celebrated observatory of Uraniborg and began observations in December, 1576, using the large instruments then found necessary in order to attain the accuracy of observation which within the next half-century was to be so greatly facilitated by the invention of the telescope. ...For more than twenty years he continued his observations at Uraniborg, surrounded by his family, and attracting numerous pupils."

"His [Tycho's] constant aim was to accumulate a large store of observations of a high order of accuracy, and thus to provide data for the complete reform of astronomy."

"Few of the Danish nobles had any sympathy with Tycho’s pursuits, and most of them strongly resented the continual expense borne by the King’s treasury. Tycho moreover was so absorbed in his scientific pursuits that he would not take the trouble to be a good landlord, nor to carry out all the duties laid upon him in return for certain of his grants of income."

"His buildings included a chemical laboratory, and he was in the habit of making up elixirs for various medical purposes; these were quite popular, particularly as he made no charge for them. He seems to have been something of a homœopathist, for he recommends sulphur to cure infectious diseases “brought on by the sulphurous vapours of the Aurora Borealis”!"

"In November, 1577, appeared a bright comet, which Tycho carefully observed with his sextant, proving that it had no perceptible parallax, and must therefore be further off than the moon. He thus definitely overthrew the common belief in the atmospheric origin of comets, which he had himself hitherto shared. With increasing accuracy he observed several other comets, notably one in 1585, when he had a full equipment of instruments and a large staff of assistants."

"The year 1588, which saw the death of his royal benefactor, saw also the publication of a volume of Tycho’s great work “Introduction to the New Astronomy”. The first volume, devoted to the new star of 1572, was not ready, because the reduction of the observations involved so much research to correct the star places for refraction, precession, etc.; it was not completed in fact until Tycho’s death, but the second volume, dealing with the comet of 1577, was printed at Uraniborg and some copies were issued in 1588. Besides the comet observations it included an account of Tycho’s system of the world."

"He [Tycho] would not accept the Copernican system, as he considered the earth too heavy and sluggish to move, and also that the authority of Scripture was against such an hypothesis. He therefore assumed that the other planets revolved about the sun, while the sun, moon, and stars revolved about the earth as a center. Geometrically this is much the same as the Copernican system, but physically it involves the grotesque demand that the whole system of stars revolves round our insignificant little earth every twenty-four hours."

"Since his previous small book on the comet, Tycho had evidently considered more fully its possible astrological significance, for he foretold a religious war, giving the date of its commencement, and also the rising of a great Protestant champion. These predictions were apparently fulfilled almost to the letter by the great religious wars that broke out towards the end of the sixteenth century, and in the person of Gustavus Adolphus."

"He [Tycho]... reached Prague in June, 1599. Rudolph granted him a salary of at least 3000 florins, promising also to settle on him the first hereditary estate that should lapse to the Crown."

"Kepler, who had been in correspondence with Tycho, consented to join him as an assistant. Another assistant, Longomontanus, who had been with Tycho at Uraniborg, was finding difficulty with the long series of Mars observations, and it was arranged that he should transfer his energies to the lunar observations, leaving those of Mars for Kepler. Before very much could be done with them, however, Tycho died at the end of October, 1601"

"It was at Uraniborg that the mass of observations was produced upon which the fame of Tycho Brahe rests. His own discoveries, though in themselves the most important made in astronomy for many centuries, are far less valuable than those for which his observations furnished the material."

"He [Tycho] discovered the third and fourth inequalities of the moon in longitude, called respectively the variation and the annual equation, also the variability of the motion of the moon’s nodes and the inclination of its orbit to the ecliptic. He obtained an improved value of the constant of precession, and did good service by rejecting the idea that it was variable, an idea which, under the name of trepidation, had for many centuries been accepted. He discovered the effect of refraction, though only approximately its amount, and determined improved values of many other astronomical constants, but singularly enough made no determination of the distance of the sun, adopting instead the ancient and erroneous value given by Hipparchus."

"His [Tycho's] magnificent Observatory of Uraniborg, the finest building for astronomical purposes that the world had hitherto seen, was allowed to fall into decay, and scarcely more than mere indications of the site may now be seen."

"Kepler was delayed by illness on the way, but ultimately reached Prague, accompanied by his wife, and for some time lived entirely at Tycho’s expense, writing by way of return essays against Reymers and another man, who had claimed the credit of the Tychonic system."

"In September, 1601, Tycho presented him [Kepler] to the Emperor, who gave him the title of Imperial Mathematician, on condition of assisting Tycho in his calculations, the very thing Kepler was most anxious to be allowed to do: for nowhere else in the world was there such a collection of good observations sufficient for his purpose of reforming the whole theory of astronomy."

"Tycho... died of acute distemper; Kepler began to prepare the mass of manuscripts for publication, but, as everything was claimed by the Brahe family, he was not allowed to finish the work. He succeeded to Tycho’s post of principal mathematician to the Emperor, at a reduced official salary. In order to meet his expenses he had recourse to the casting of nativities, for which he gained considerable reputation and received very good pay. He worked by the conventional rules of astrology, and was quite prepared to take fees for so doing, although he had very little faith in them, preferring his own fanciful ideas."

"In 1604 the constellation of Cassiopeia was once more temporarily enriched by the appearance of a new star... Kepler at once wrote a short account of it... He made no secret of his views on conventional astrology, as to which he claimed to speak with the authority of one fully conversant with its principles, but he nevertheless expressed his sincere conviction that the conjunctions and aspects of the planets certainly did affect things on the earth, maintaining that he was driven to this belief against his will by “most unfailing experiences”."

"In 1604 he [Kepler] published “A Supplement to Vitellion,” containing the earliest known reasonable theory of optics, and especially of dioptrics or vision through lenses. He compared the mechanism of the eye with that of Porta’s “Camera Obscura,” but made no attempt to explain how the image formed on the retina is understood by the brain. He went carefully into the question of refraction, the importance of which Tycho had been the first astronomer to recognize, though he only applied it at low altitudes, and had not arrived at a true theory or accurate values."

"Kepler wasted a good deal of time and ingenuity on trial theories. He would invariably start with some hypothesis, and work out the effect. He would then test it by experiment, and when it failed would at once recognize that his hypothesis was a priori bound to fail. He rarely seems to have noticed the fatal objections in time to save himself trouble. He would then at once start again on a new hypothesis, equally gratuitous and equally unfounded. It never seems to have occurred to him that there might be a better way of approaching a problem."

"Not many years later Snell discovered the true law of refraction, but Kepler’s contribution to the subject, though he failed to discover the actual law, includes several of the adopted “by-laws”. He noted that atmospheric refraction would alter with the height of the atmosphere and with temperature, and also recognized the fact that rainbow colors depend on the angle of refraction, whether seen in the rainbow itself, or in dew, glass, water, or any similar medium. He thus came near to anticipating Newton."

"After hearing of Galileo’s telescope, Kepler suggested that for astronomical purposes two convex lenses should be used, so that there should be a real image where measuring wires could be placed for reference. He did not carry out the idea himself, and it was left to the Englishman Gascoigne to produce the first instrument on this “Keplerian” principle, universally known as the Astronomical Telescope."

"In 1606 came a second treatise on the new star... This was followed in 1607 by a treatise on comets, suggested by the comet appearing that year, known as Halley’s comet after its next return. He regarded comets as “planets” moving in straight lines, never having examined sufficient observations of any comet to convince himself that their paths are curved."

"Another suggestive remark of his [Kepler's] was to the effect that the planets must be self-luminous, as otherwise Mercury and Venus, at any rate, ought to show phases. This was put to the test not long afterwards by means of Galileo’s telescope."

"In 1607 Kepler rushed into print with an alleged observation of Mercury crossing the sun, but after Galileo’s discovery of sun-spots, Kepler at once cheerfully retracted his observation of “Mercury,” and... warmly adopted Galileo’s side... Maestlin and others of Kepler’s friends took the opposite view."

"When Gilbert of Colchester, in his “New Philosophy,” founded on his researches in magnetism, was dealing with tides, he did not suggest that the moon attracted the water, but that “subterranean spirits and humours, rising in sympathy with the moon, cause the sea also to rise and flow to the shores and up rivers”. It appears that an idea, presented in some such way as this, was more readily received than a plain statement. This so-called philosophical method was, in fact, very generally applied, and Kepler, who shared Galileo’s admiration for Gilbert’s work, adopted it in his own attempt to extend the idea of magnetic attraction to the planets."

"The general idea of “gravity” opposed the hypothesis of the rotation of the earth on the ground that loose objects would fly off: moreover, the latest refinements of the old system of planetary motions necessitated their orbits being described about a mere empty point. Kepler very strongly combated these notions, pointing out the absurdity of the conclusions to which they tended, and proceeded in set terms to describe his own theory."

"“Every corporeal substance, so far forth as it is corporeal, has a natural fitness for resting in every place where it may be situated by itself beyond the sphere of influence of a body cognate with it. Gravity is a mutual affection between cognate bodies towards union or conjunction (similar in kind to the magnetic virtue), so that the earth attracts a stone much rather than the stone seeks the earth. ...wheresoever the earth may be placed, or whithersoever it may be carried by its animal faculty, heavy bodies will always be carried towards it. If the earth were not round, heavy bodies would not tend from every side in a straight line towards the centre of the earth, but to different points from different sides. If two stones were placed... near each other, and beyond the sphere of influence of a third cognate body, these stones, like two magnetic needles, would come together in the intermediate point, each approaching the other by a space proportional to the comparative mass of the other. If the moon and earth were not retained in their orbits by their animal force or some other equivalent, the earth would mount to the moon by a fifty-fourth part of their distance, and the moon fall towards the earth through the other fifty-three parts, and they would there meet, assuming, however, that the substance of both is of the same density. If the earth should cease to attract its waters to itself all the waters of the sea would he raised and would flow to the body of the moon. The sphere of the attractive virtue which is in the moon extends as far as the earth, and entices up the waters; but as the moon flies rapidly across the zenith, and the waters cannot follow so quickly, a flow of the ocean is occasioned in the torrid zone towards the westward. If the attractive virtue of the moon extends as far as the earth, it follows with greater reason that the attractive virtue of the earth extends as far as the moon and much farther; and, in short, nothing which consists of earthly substance anyhow constituted although thrown up to any height, can ever escape the powerful operation of this attractive virtue. Nothing which consists of corporeal matter is absolutely light, but that is comparatively lighter which is rarer, either by its own nature, or by accidental heat. And it is not to be thought that light bodies are escaping to the surface of the universe while they are carried upwards, or that they are not attracted by the earth. They are attracted, but in a less degree, and so are driven outwards by the heavy bodies; which being done, they stop, and are kept by the earth in their own place. But although the attractive virtue of the earth extends upwards, as has been said, so very far, yet if any stone should be at a distance great enough to become sensible compared with the earth’s diameter, it is true that on the motion of the earth such a stone would not follow altogether; its own force of resistance would be combined with the attractive force of the earth, and thus it would extricate itself in some degree from the motion of the earth.” The above passage from the Introduction to Kepler’s “Commentaries on the Motion of Mars,” always regarded as his most valuable work, must have been known to Newton, so that no such incident as the fall of an apple was required to provide a necessary and sufficient explanation of the genesis of his Theory of Universal Gravitation. Kepler’s glimpse at such a theory could have been no more than a glimpse, for he went no further with it. This seems a pity, as it is far less fanciful than many of his [Kepler's] ideas, though not free from the “virtues” and “animal faculties,” that correspond to Gilbert’s “spirits and humours”."

"Reviewing the suggestions of the ancient Greeks, he [ Copernicus ] was struck by the simplification that would be introduced by reviving the idea that the annual motion should be attributed to the earth itself instead of having a separate annual epicycle for each planet and for the sun. Of the seventy odd circles or epicycles required by the latest form of the Ptolemaic system, Copernicus succeeded in dispensing with rather more than half, but he still required thirty-four, which was the exact number assumed before the time of Aristotle."

"In Spain... in the thirteenth century Alphonso of Castile, with the assistance of Jewish and Christian computers, compiled the Alphonsine tables, completed in 1252."

"After Ptolemy’s time very little was heard for many centuries of any fresh planetary theory, though advances in some points of detail were made, notably by some of the Arab philosophers, who obtained improved values for some of the elements by using better instruments. From time to time various modifications of Ptolemy’s theory were suggested, but none of any real value."