* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download solar system
James Webb Space Telescope wikipedia , lookup
History of Solar System formation and evolution hypotheses wikipedia , lookup
Astrobiology wikipedia , lookup
Kepler (spacecraft) wikipedia , lookup
Theoretical astronomy wikipedia , lookup
Formation and evolution of the Solar System wikipedia , lookup
Definition of planet wikipedia , lookup
Astronomy in the medieval Islamic world wikipedia , lookup
History of the telescope wikipedia , lookup
De revolutionibus orbium coelestium wikipedia , lookup
Astronomical unit wikipedia , lookup
Spitzer Space Telescope wikipedia , lookup
Lunar theory wikipedia , lookup
Chinese astronomy wikipedia , lookup
International Ultraviolet Explorer wikipedia , lookup
Astrophotography wikipedia , lookup
International Year of Astronomy wikipedia , lookup
Satellite system (astronomy) wikipedia , lookup
Extraterrestrial life wikipedia , lookup
Galileo affair wikipedia , lookup
Exploration of Io wikipedia , lookup
History of astronomy wikipedia , lookup
Copernican heliocentrism wikipedia , lookup
Observational astronomy wikipedia , lookup
Ancient Greek astronomy wikipedia , lookup
Geocentric model wikipedia , lookup
Hebrew astronomy wikipedia , lookup
Patronage in astronomy wikipedia , lookup
Timeline of astronomy wikipedia , lookup
Dialogue Concerning the Two Chief World Systems wikipedia , lookup
solar system Collection Editor: Joel Thierstein solar system Collection Editor: Joel Thierstein Author: Albert Van Helden Online: < http://cnx.org/content/col10432/1.1/ > CONNEXIONS Rice University, Houston, Texas This selection and arrangement of content as a collection is copyrighted by Joel Thierstein. It is licensed under the Creative Commons Attribution 2.0 license (http://creativecommons.org/licenses/by/2.0/). Collection structure revised: June 29, 2007 PDF generated: October 26, 2012 For copyright and attribution information for the modules contained in this collection, see p. 61. Table of Contents 1 (Untitled) 2 Copernican System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3 Galileo's Telescope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 4 Johannes Kepler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 5 Ptolemaic System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 6 Satellites of Jupiter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 7 Saturn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 8 Sunspots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 9 The Biography of Galileo Galilei . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 10 The Moon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Bibliography Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 Attributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 iv Available for free at Connexions <http://cnx.org/content/col10432/1.1> Chapter 1 (Untitled) Available for free at Connexions <http://cnx.org/content/col10432/1.1> 1 2 CHAPTER 1. (UNTITLED) Available for free at Connexions <http://cnx.org/content/col10432/1.1> Chapter 2 Copernican System Figure 2.1: 1 Copernicus The rst speculations about the possibility of the Sun being the center of the cosmos and the Earth being one of the planets going around it go back to the third century BCE. In his Sand-Reckoner, Archimedes (d. 212 BCE), discusses how to express very large numbers. As an example he chooses the question as to how many grains of sand there are in the cosmos. And in order to make the problem more dicult, he chooses not the geocentric cosmos generally accepted at the time, but the heliocentric cosmos proposed by Aristarchus of Samos (ca. 310-230 BCE), which would have to be many times larger because of the lack of observable stellar parallax. We know, therefore, that already in Hellenistic times thinkers were at least toying with this notion, and because of its mention in Archimedes's book Aristarchus's speculation was well-known in Europe beginning in the High Middle Ages but not seriously entertained until Copernicus. 1 This content is available online at <http://cnx.org/content/m11938/1.3/>. Available for free at Connexions <http://cnx.org/content/col10432/1.1> 3 CHAPTER 2. COPERNICAN SYSTEM 4 Figure 2.2: Copernicus European learning was based on the Greek sources that had been passed down, and cosmological and astronomical thought were based on Aristotle and Ptolemy (Chapter 5). Aristotle's cosmology of a central Earth surrounded by concentric spherical shells carrying the planets and xed stars was the basis of European thought from the 12th century CE onward. Technical astronomy, also geocentric, was based on the constructions of excentric circles and epicycles codied in Ptolemy's Almagest (2d. century CE). In the fteenth century, the reform of European astronomy was begun by the astronomer/humanist Georg Peurbach (1423-1461) and his student Johannes Regiomontanus (1436-1476). Their eorts (like those of their colleagues in other elds) were concentrated on ridding astronomical texts, especially Ptolemy's, from errors by going back to the original Greek texts and providing deeper insight into the thoughts of the original authors. With their new textbook and a guide to the Almagest, Peurbach and Regiomontanus raised the level of theoretical astronomy in Europe. Several problems were facing astronomers at the beginning of the sixteenth century. First, the tables (by means of which to predict astronomical events such as eclipses and conjunctions) were deemed not to be suciently accurate. Second, Portuguese and Spanish expeditions to the Far East and America sailed out of sight of land for weeks on end, and only astronomical methods could help them in nding their locations on the high seas. Third, the calendar, instituted by Julius Caesar in 44 BCE was no longer accurate. The equinox, which at the time of the Council of Nicea (325 CE) had fallen on the 21st, had now slipped to the 11th. Since the date of Easter (the celebration of the dening event in Christianity) was determined with reference to the equinox, and since most of the other religious holidays through the year were counted forward or backward from Easter, the slippage of the calendar with regard to celestial events was a very serious problem. For the solution to all three problems, Europeans looked to the astronomers. Nicholas Copernicus (1473-1543) learned the works of Peurbach and Regiomontanus in the undergraduate curriculum at the university of Cracow and then spent a decade studying in Italy. Upon his return to Poland, he spent the rest of his life as a physician, lawyer, and church administrator. During his spare time he continued his research in astronomy. The result was De Revolutionibus Orbium Coelestium ("On the Revolutions of the Celestial Orbs"), which was published in Nuremberg in 1543, the year of his death. The Available for free at Connexions <http://cnx.org/content/col10432/1.1> 5 book was dedicated to Pope Paul III and initially caused litle controversy. An anonymous preface (added by Andreas Osiander, the Protestant reformer of Nuremberg) stated that the theory put forward in this book was only a mathematical hypothesis: the geometrical constructions used by astronomers had traditionally had only hypothetical status; cosmological interpretations were reserved for the philosophers. Indeed, except for the rst eleven chapters of Book I, of the Almagest. Figure 2.3: De Revolutionibus was a technical mathematical work in the tradition Diagram of the Copernican system, from De Revolutions2 But in the rst book, Copernicus stated that the Sun was the center of the universe and that the Earth had a triple motion 3 around this center. His theory gave a simple and elegant explanation of the retrograde motions of the planets (the annual motion of the Earth necessarily projected onto the motions of the planets in geocentric astronomy) and settled the order of the planets (which had been a convention in Ptolemy's work) denitively. He argued that his system was more elegant than the traditional geocentric system. Copernicus still retained the priviledged status of circular motion and therefore had to construct his planetary orbits from circles upon and within circles, just as his predecessors had done. His tables were perhaps only marginally better than existing ones. The reception of De Revolutionibus was mixed. The heliocentric hypothesis was rejected out of hand by virtually all, but the book was the most sophisticated astronomical treatise since the Almagest, and for this it was widely admired. Its mathematical constructions were easily transferred into geocentric ones, and many astronomers used them. In 1551 Erasmus Reinhold, no believer in the mobility of the Earth, Prutenic Tables, based on Copernicus's parameters. These tables came accuracy. Further, De revolutionibus became the central work in a network of published a new set of tables, the to be preferred for their astronomers, who dissected it in great detail. Not until a generation after its appearance, however, can we begin point to a community of practicing astronomers who accepted heliocentric cosmology. the most remarkable early follower of Copernicus was Thomas Digges (c. Description of the Coelestiall Orbes (1576) Perhaps A Pert De Revolutionibus into 1545-c.1595), who in translated a large part of Book I of English and illustrated it with a diagram in which the Copernican arrangement of the planets is imbedded in an innite universe of stars. 2 http://cnx.org/content/m11938/latest/copernican_universe.gif 3 A daily rotation about its center, an annual motion around the Sun, and a conical motion of its axis of rotation. This last motion was made necessary because Copernicus conceptualized the Earth's annual motion as the result of the Earth being embedded in a spherical shell centered on the Sun. Its axis of rotation therefore did not remain parallel to itself with respect to the xed stars. To keep the axis parallel to itself, Copernicus gave the axis a conical motion with a period just about equal to the year. The very small dierence from the annual period accounted for the precesion of the equinoxes, an eect caused by the fact that the Earth's axis (in Newtonian terms) precesses like a top, with a period of about 26,000 years. (Copernicus's ideas about this precession were more cumbersome and based on faulty data.) Available for free at Connexions <http://cnx.org/content/col10432/1.1> CHAPTER 2. COPERNICAN SYSTEM 6 Figure 2.4: Diagram of the universe by Thomas Digges4 The reason for this delay was that, on the face of it, the heliocentric cosmology was absurd from a common-sensical and a physical point of view. Thinkers had grown up on the Aristotelian division between the heavens and the earthly region, between perfection and corruption. In Aristotle's physics, bodies moved to their natural places. Stones fell because the natural place of heavy bodies was the center of the universe, and that was why the Earth was there. Accepting Copernicus's system meant abandoning Aristotelian physics. How would birds nd their nest again after they had own from them? Why does a stone thrown up come straight down if the Earth underneath it is rotating rapidly to the east? Since bodies can only have one sort of motion at a time, how can the Earth have several? And if the Earth is a planet, why should it be the only planet with a moon? For astronomical purposes, astronomers always assumed that the Earth is as a point with respect to the ◦ heavens. Only in the case of the Moon could one notice a parallactic displacement (about 1 ) with respect to the xed stars during its (i.e., the Earth's) diurnal motion. In Copernican astronomy one now had to assume that the orbit of the Earth was as a point with respect to the xed stars, and because the xed stars did not reect the Earth's annual motion by showing an annual parallax, the sphere of the xed stars had to be immense. What was the purpose of such a large space between the region of Saturn and that of the xed stars? 4 http://cnx.org/content/m11938/latest/digges_universe.gif Available for free at Connexions <http://cnx.org/content/col10432/1.1> 7 Parallax5 Figure 2.5: These and others were objections that needed answers. The Copernican system simply did not t into the Aristotelian way of thinking. It took a century and a half for a new physics to be devised to undegird heliocentric astronomy. The works in physics and astronomy of Galileo and Johannes Kepler (Chapter 4) were crucial steps on this road. There was another problem. A stationary Sun and moving Earth also clashed with many biblical passages. Protestants and Catholics alike often dismissed heliocentrism on these grounds. Martin Luther did so in one of his "table talks" in 1539, before De Revolutionibus had appeared. (Preliminary sketches had circulated in manuscript form.) In the long run, Protestants, who had some freedom to interpret the bible personally, accepted heliocentrism somewhat more quickly. Catholics, especially in Spain and Italy, had to be more cautious in the religious climate of the Counter Reformation, as the case of Galileo clearly demonstrates. 6 Christoph Clavius , the leading Jesuit mathematician from about 1570 to his death in 1612, used biblical arguments against heliocentrism in his astronomical textbook. The situation was never simple, however. 7 For one thing, late in the sixteenth century Tycho Brahe devised a hybrid geostatic heliocentric system in which the Moon and Sun went around the Earth but the planets went around the Sun. In this system the elegance and harmony of the Copernican system were married to the solidity of a central and stable Earth so that Aristotelian physics could be maintained. Especially after Galileo's telescopic discoveries, many astronomers switched from the traditional to the Tychonic cosmology. For another thing, by 1600 there were still very few astronomers who accepted Copernicus's 8 cosmology. It is not clear whether the execution of Giordano Bruno , a Neoplatonist mystic who knew little about astronomy, had anything to do with his Copernican beliefs. Finally, we must not forget that Copernicus had dedicated De Revolutionibus to the Pope. During the sixteenth century the Copernican issue was not considered important by the Church and no ocial pronouncements were made. Galileo's discoveries changed all that. Beginning with Sidereus Nuncius in 1610, Galileo brought the issue before a wide audience. He continued his eorts, ever more boldly, in his letters on sunspots, and in his letter to the Grand Duchess Christina (circulated in manuscript only) he actually interpreted the problematical biblical passage in the book of Joshua to conform to a heliocentric cosmology. More importantly, he argued that the Bible is written in the language of the common person who is not an expert in astronomy. Scripture, he argued, teaches us how to go to heaven, not how the heavens go. At about the same time, Paolo Antonio 9 Foscarini , a Carmelite theologian in Naples, published a book in which he argued that the Copernican 5 http://cnx.org/content/m11938/latest/parallax.gif 6 "Christopher Clavius" <http://cnx.org/content/m11958/latest/> 7 "Tycho Brahe" <http://cnx.org/content/m11946/latest/> 8 "Giordano Bruno (1548-1600)" <http://cnx.org/content/m11935/latest/> 9 "Paolo Antonio Foscarini" <http://cnx.org/content/m11966/latest/> Available for free at Connexions <http://cnx.org/content/col10432/1.1> CHAPTER 2. COPERNICAN SYSTEM 8 theory did not conict with Scripture. It was at this point that Church ocials took notice of the Copernican De Revolutionibus on the Index of Forbidden Books10 until corrected. Dialogue Concerning the Two Chief World Systems of 1632 was a watershed in what had shaped theory and placed Galileo's up to be the "Great Debate." Galileo's arguments undermined the physics and cosmology of Aristotle for an increasingly receptive audience. His telescopic discoveries, although they did not prove that the Earth moved around the Sun, added greatly to his argument. In the meantime, Johannes Kepler (Chapter 4) (who had died in 1630) had introduced physical considerations into the heavens and had published his Tables, based on his own elliptical theory and Tycho Brahe's11 Rudolphine accurate observations, and these tables were more accurate by far than any previous ones. The tide now ran in favor of the heliocentric theory, and from the middle of the seventeenth century there were few important astronomers who were not Copernicans. 10 "The Congregation of the Index" <http://cnx.org/content/m11974/latest/> 11 "Tycho Brahe" <http://cnx.org/content/m11946/latest/> Available for free at Connexions <http://cnx.org/content/col10432/1.1> Chapter 3 1 Galileo's Telescope Figure 3.1: Johannes Hevelius observing with one of his telescopes.2 (Source: Selenographia, 1647) The telescope was one of the central instruments of what has been called the Scientic Revolution of the seventeenth century. It revealed hitherto unsuspected phenomena in the heavens and had a profound inuence on the controversy between followers of the traditional geocentric astronomy (Chapter 5) and cosmology and 3 those who favored the heliocentric system of Copernicus . It was the rst extension of one of man's senses, and demonstrated that ordinary observers could see things that the great Aristotle had not dreamed of. It therefore helped shift authority in the observation of nature from men to instruments. In short, it was the prototype of modern scientic instruments. But the telescope was not the invention of scientists; rather, it was the product of craftsmen. For that reason, much of its origin is inaccessible to us since craftsmen were by and large illiterate and therefore historically often invisible. Although the magnifying and diminishing properties of convex and concave transparent objects was known in Antiquity, lenses as we know them were introduced in the West 4 at the end of the thirteenth century. Glass of reasonable quality had become relatively cheap and in the major glass-making centers of Venice and Florence techniques for grinding and polishing glass had reached a high state of development. Now one of the perennial problems faced by aging scholars could be solved. With age, the eye progressively 1 This content is available online at <http://cnx.org/content/m11932/1.4/>. 2 http://cnx.org/content/m11932/latest/hevelius_telescope.gif 3 "Introduction" <http://cnx.org/content/m11838/latest/> 4 They may have developed independently in China. Available for free at Connexions <http://cnx.org/content/col10432/1.1> 9 CHAPTER 3. GALILEO'S TELESCOPE 10 loses its power to accommodate, that is to change its focus from faraway objects to nearby ones. This condition, known as presbyopia, becomes noticeable for most people in their forties, when they can no longer focus on letters held at a comfortable distance from the eye. Magnifying glasses became common in the thirteenth century, but these are cumbersome, especially when one is writing. Craftsmen in Venice began making small disks of glass, convex on both sides, that could be worn in a framespectacles. Because these little disks were shaped like lentils, they became known as "lentils of glass," or (from the Latin) lenses. The earliest illustrations of spectacles date from about 1350, and spectacles soon came to be symbols of learning. Figure 3.2: The Spectacle Vendor by Johannes Stradanus, engraved by Johannes Collaert, 15825 These spectacles were, then, reading glasses. When one had trouble reading, one went to a spectaclemaker's shop or a peddler of spectacles (see Figure 3.2 and Figure 3.3) and found a suitable pair by trial and error. They were, by and large, glasses for the old. spectacles for the young, concave lenses 6 that correct the refractive error known as myopia, were rst made (again in Italy) in the middle of the fteenth century. So by about 1450 the ingredients for making a telescope were there. The telescopic eect can be achieved by several combinations of concave and convex mirrors and lenses. Why was the telescope not invented in the fteenth century? There is no good answer to this question, except perhaps that lenses and mirrors of the appropriate strengths were not available until later. In the literature of white magic, so popular in the sixteenth century, there are several tantalizing references to devices that would allow one to see one's enemies or count coins from a great distance. But these allusions were cast in obscure language and were accompanied by fantastic claims; the telescope, when it came, was a very humble and simple device. It is possible that in the 1570s Leonard and Thomas Digges in England actually made an instrument consisting of a convex lens and a mirror, but if this proves to be the case, it was an experimental setup that was never translated into a mass-produced device. 5 http://cnx.org/content/m11932/latest/spectacle_maker2.gif 6 Note that the word lens was used only to denote convex lenses until the end 7 The claim for an "Elizabethan telescope" has recently been made by Colin based on the writings of Thomas Digges and William Bourne. 7 of the seventeenth century. Ronin, who has demonstrated an instrument Available for free at Connexions <http://cnx.org/content/col10432/1.1> 11 The earliest known illlustration of a telescope. Giovanpattista della Porta included this sketch in a letter written in August 1609.8 Figure 3.3: The telescope was unveiled in the Netherlands. In October 1608, the States General (the national 9 of Middelburg, and government) in The Hague discussed the patent applications rst of Hans Lipperhey then of Jacob Metius of Alkmaar, on a device for "seeing faraway things as though nearby." It consisted of a convex and concave lens in a tube, and the combination magnied three or four times. 10 The gentlemen found the device too easy to copy to award the patent, but it voted a small award to Metius and employed Lipperhey to make several binocular versions, for which he was paid handsomely. It appears that another citizen of Middelburg, Sacharias Janssen had a telescope at about the same time but was at the Frankfurt Fair where he tried to sell it. Figure 3.4: Galileo's telescopes11 The news of this new invention spread rapidly through Europe, and the device itself quickly followed. By April 1609 three-powered spyglasses could be bought in spectacle-maker's shops on the Pont Neuf in Paris, 12 observed and four months later there were several in Italy. (Figure 3.4) We know that Thomas Harriot the Moon (Chapter 10) with a six-powered instrument early in August 1609. But it was Galileo who made the instrument famous. He constructed his rst three-powered spyglass in June or July 1609, presented an eight-powered instrument to the Venetian Senate in August, and turned a twenty-powered instrument to the heavens in October or November. With this instrument (Figure 3.5) he observed the Moon, discovered four satellites of Jupiter (Chapter 6), and resolved nebular patches into stars. He published Sidereus Nuncius in March 1610. Verifying Galileo's discoveries was initially dicult. In the spring of 1610 no one had telescopes of sucient quality and power to see the satellites of Jupiter, although many had weaker instruments with which they could see some of the lunar detail Galileo had described in Sidereus Nuncius. Galileo's lead was one of practice, not theory, and it took about six months before others could make or obtain instruments good enough to see Jupiter's moons. With the verication of the phases of Venus by others, in the rst half 8 http://cnx.org/content/m11932/latest/porta_sketch.gif 9 "Hans Lipperhey" <http://cnx.org/content/m11940/latest/> 10 Their optical system and magnication was the same as our traditional 11 http://cnx.org/content/m11932/latest/g_telescope.gif 12 "Thomas Harriot" <http://cnx.org/content/m11979/latest/> opera glasses. Available for free at Connexions <http://cnx.org/content/col10432/1.1> CHAPTER 3. GALILEO'S TELESCOPE 12 of 1611, Galileo's lead in telescope-making had more or less evaporated. The next discovery, that of sunspots (Chapter 8), was made by several observers, including Galileo, independently. Figure 3.5 A typical Galilean telescope with which Jupiter's moons could be observed was congured as follows. It had a plano-convex objective (the lens toward the object) with a focal length of about 30-40 inches., and a plano-concave ocular with a focal length of about 2 inches. The ocular was in a little tube that could be adjusted for focusing. The objective lens was stopped down to an aperture of 0.5 to 1 inch. , and the eld of view was about 15 arc-minutes (about 15 inches in 100 yards). The instrument's magnication was 15-20. The glass was full of little bubbles and had a greenish tinge (caused by the iron content of the glass); the shape of the lenses was reasonable good near their centers but poor near the periphery (hence the restricted aperture); the polish was rather poor. The limiting factor of this type of instrument was its small eld of viewabout 15 arc-minuteswhich meant that only a quarter of the full Moon could be accommodated in the eld. Over the next several decades, lens-grinding and polishing techniques improved gradually, as a specialized craft of telescope makers slowly developed. But although Galilean telescopes of higher magnications were certainly made, they were almost useless because of the concomitant shrinking of the eld. As mentioned above, the telescopic eect can be achieved with dierent combinations of lenses and mirrors. As early as 1611, in his Dioptrice, Johannes Kepler (Chapter 4) had shown that a telescope could also be made by combining a convex objective and a convex ocular. He pointed out that such a combination would produce an inverted image but showed that the addition of yet a third convex lens would make the image erect again. This suggestion was not immediately taken up by astronomers, however, and it was not until Christoph Scheiner 13 published his Rosa Ursina in 1630 that this form of telescope began to spread. In his study of sunspots, Scheiner had experimented with telescopes with convex oculars in order to make the image of the Sun projected through the telescope erect. 14 But when he happened to view an object directly through such an instrument, he found that, although the image was inverted, it was much brighter and the eld of view much larger than in a Galilean telescope. Since for astronomical observations an inverted image is no problem, the advantages of what became known as the astronomical telescope led to its general acceptance in the astronomical community by the middle of the century. 13 "Christoph Scheiner" <http://cnx.org/content/m12126/latest/> 14 The Galilean telescope produces an erect image of an object viewed directly but an inverted image of a projected object; by substituting a convex for the concave ocular, this situation is reversed. Available for free at Connexions <http://cnx.org/content/col10432/1.1> 13 The Galilean telescope could be used for terrestrial and celestial purposes interchangeably. This was not true for the astronomical telescope with its inverted image. Astronomers eschewed the third convex lens (the erector lens) necessary for re-inverting the image because the more lenses the more optical defects multiplied. In the second half of the seventeenth century, therefore, the Galilean telescope was replaced for terrestrial purposes by the "terrestrial telescope," which had four convex lenses: objective, ocular, erector lens, and a eld lens (which enlarged the eld of view even further). (a) (b) Figure 3.6: 16 scope (Machina Coelestis, 1673) (a) Hevelius's 60 foot telescope15 (b) Hevelius's 140 foot tele- With the acceptance of the astronomical telescope, the limit on magnication caused by the small eld of view of the Galilean telescope was temporarily lifted, and a "telescope race" developed. Because of optical defects, the curvature of lenses had to be minimized, and therefore (since the magnication of a simple telescope is given roughly by the ratio of the focal lengths of the objective and ocular) increased magnication had to be achieved by increasing the focal length of the objective. Beginning in the 1640s, the length of telescopes began to increase. From the typical Galilean telescope of 5 or 6 feet in length, astronomical telescopes rose to lengths of 15 or 20 feet by the middle of the century. A typical astronomical telescope is the one made by Christiaan Huygens, in 1656. It was 23 feet long; its objective had an aperture 15 http://cnx.org/content/m11932/latest/hevelius_telescope_60ft.gif 16 http://cnx.org/content/m11932/latest/hevelius_telescope_140ft.gif Available for free at Connexions <http://cnx.org/content/col10432/1.1> CHAPTER 3. GALILEO'S TELESCOPE 14 of several inches, it magnied about 100 times, and its eld of view was 17 arc-minutes. Figure 3.7: Aerial telescope (Christiaan Huygensm Astroscopium Compendiaria,1684)17 Telescopes had now again reached the point where further increases in magnication would restrict the eld of view of the instrument too much. This time another optical device, the eld lens came to the rescue. Adding a third convex lensof appropriate focal length, and in the right placeincreased the eld signicantly, thus allowing higher magnications. The telescope race therefore continued unabated and lengths increased exponentially. By the early 1670s, Johannes Hevelius had built a 140-foot telescope. But such long telescopes were useless for observation: it was almost impossible to keep the lenses aligned and any wind would make the instrument utter. After about 1675, therefore, astronomers did away with the telescope tube. The objective was mounted on a building or pole by means of a ball-joint and aimed by means of a string; the image was found by trial and error; and the compound eyepiece (eld lens and ocular), on a little stand, was then positioned to receive the image cast by the objective. Such instruments were called aerial telescopes. Although some discoveries were made with these very long instruments, this form of telescope had reached its limits. By the beginning of the eighteenth century very long telescopes were rarely mounted any more, and further increases of power came, beginning in the 1730s, from a new form of telescope, the reecting telescope. Since it was known that the telescopic eect could be achieved using a variety of combinations of lenses and mirrors, a number of scientists speculated on combinations involving mirrors. Much of this speculation was fueled by the increasingly rened theoretical study of the telescope. In his Dioptrique, appended to his Discourse on Method of 1637, Renè Descartes addressed the problem of spherical aberration, already pointed out by others. In a thin spherical lens, not all rays from innityincident parallel to the optical axisare united at one point. Those farther from the optical axis come to a focus closer to the back of the lens than those nearer the optical axis. Descartes had either learned the sine law of refraction from Willebrord Snell (Snell's Law) 18 or had discovered it independently, and this allowed him to quantify spherical aberration. In order to eliminate it, he showed, lens curvature had to be either plano-hyperboloidal or spherico-ellipsoidal. His demonstration led many to attempt to make plano-hyperboloidal objectives, 19 an eort which was doomed to failure by the state of the art of lens-grinding. Others began considering the virtues of a concave paraboloidal mirror as primary receptor: it had been known since Antiquity that such a mirror would bring parallel incident rays to a focus at one point. 17 http://cnx.org/content/m11932/latest/aerial_telescope.gif 18 The ratio of the sines of the angles of incidence and refraction is constant. 19 The eect is most apparent for the objective; spherical aberration in the ocular aects the image much less. Available for free at Connexions <http://cnx.org/content/col10432/1.1> 15 Figure 3.8: Newton's reecting telescope (1671)20 A second theoretical development came in 1672, when Isaac Newton published his celebrated paper on light and colors. Newton showed that white light is a mixture of colored light of dierent refrangibility: every color had its own degree of refraction. The result was that any curved lens would decompose white light into the colors of the spectrum, each of which comes to a focus at a dierent point on the optical axis. This eect, which became known as chromatic aberration, resulted in a central image of, e.g., a planet, being surrounded by circles of dierent colors. Newton had developed his theory of light several years before publishing his paper, when he had turned his mind to the improvement of the telescope, and he had despaired of ever ridding the objective of this defect. He therefore decided to try a mirror, but unlike his predecessors he was able to put his idea into practice. He cast a two-inch mirror blank of speculum metal (basically copper with some tin) and ground it into spherical curvature. He placed it in the bottom of a tube and caught the reected rays on a 45 ◦ secondary mirror which reected the image into a convex ocular lens outside the tube (see Figure 3.8). He sent this little instrument to the Royal Society, where it caused a sensation; it was the rst working reecting telescope. But the eort ended there. Others were unable to grind mirrors of regular curvature, and to add to the problem, the mirror tarnished and had to be repolished every few months, with the attending danger of damage to the curvature. Figure 3.9: Hevelius's rooftop observatory, (Machina Coelestis, 1673)21 20 http://cnx.org/content/m11932/latest/newton_telescope.gif Available for free at Connexions <http://cnx.org/content/col10432/1.1> CHAPTER 3. GALILEO'S TELESCOPE 16 The reecting telescope therefore remained a curiosity for decades. In second and third decades of the eighteenth century, however, the reecting telescope became a reality in the hands of rst James Hadley and then others. By the middle of the century, reecting telescopes with primary mirrors up to six inches in diameter had been made. It was found that for large aperture ratios (the ratio of focal length of the primary to its aperture, as the f-ratio in modern cameras for instance), f/10 or more, the dierence between spherical and paraboloidal mirrors was negligible in the performance of the telescope. In the second half of the eighteenth century, in the hands of James Short and then William Herschel, the reecting telescope with parabolically ground mirrors came into its own. 21 http://cnx.org/content/m11932/latest/hevelius_roof_obsry.gif Available for free at Connexions <http://cnx.org/content/col10432/1.1> Chapter 4 Johannes Kepler Figure 4.1: 1 Johannes Kepler Johannes Kepler was born in Weil der Stadt in Swabia, in southwest Germany. His paternal grandfather, Sebald Kepler, was a respected craftsman who served as mayor of the city; his maternal grandfather, Melchior Guldenmann, was an innkeeper and mayor of the nearby village of Eltingen. His father, Heinrich Kepler, was "an immoral, rough and quarrelsome soldier," according to Kepler, and he described his mother in similar unattering terms. From 1574 to 1576 Johannes lived with his grandparents; in 1576 his parents moved to nearby Leonberg, where Johannes entered the Latin school. In 1584 he entered the Protestant seminary at Adelberg, and in 1589 he began his university education at the Protestant university of T\x{00FC}bingen. Here he studied theology and read widely. He passed the M.A. examination in 1591 and continued his studies as a graduate student. Kepler's teacher in the mathematical subjects was Michael Maestlin (1580-1635). Maestlin was one of the earliest astronomers to subscribe to Copernicus's heliocentric theory, although in his university lectures he taught only the Ptolemaic system. Only in what we might call graduate seminars did he acquaint his students, among whom was Kepler, with the technical details of the Copernican system (Chapter 2). Kepler stated later that at this time he became a Copernican for "physical or, if you prefer, metaphysical reasons." 1 This content is available online at <http://cnx.org/content/m11962/1.2/>. Available for free at Connexions <http://cnx.org/content/col10432/1.1> 17 CHAPTER 4. JOHANNES KEPLER 18 In 1594 Kepler accepted an appointment as professor of mathematics at the Protestant seminary in Graz (in the Austrian province of Styria). He was also appointed district mathematician and calendar maker. Kepler remained in Graz until 1600, when all Protestants were forced to convert to Catholicism or leave the province, as part of Counter Reformation measures. For six years, Kepler taught arithmetic, geometry (when there were interested students), Virgil, and rhetoric. In his spare time he pursued his private studies in astronomy and astrology. In 1597 Kepler married Barbara Muller. In that same year he published his rst important work, The Cosmographic Mystery, in which he argued that the distances of the planets from the Sun in the Copernican system were determined by the ve regular solids, if one supposed that a planet's orbit was circumscribed about one solid and inscribed in another. Available for free at Connexions <http://cnx.org/content/col10432/1.1> 19 Kepler's model to explain the relative distances of the planets from the Sun in the Copernican System. Figure 4.2: Except for Mercury, Kepler's construction produced remarkably accurate results. Because of his talent 2 to Prague to become his as a mathematician, displayed in this volume, Kepler was invited by Tycho Brahe 2 "Tycho Brahe" <http://cnx.org/content/m11946/latest/> Available for free at Connexions <http://cnx.org/content/col10432/1.1> CHAPTER 4. JOHANNES KEPLER 20 assistant and calculate new orbits for the planets from Tycho's observations. Kepler moved to Prague in 1600. Kepler served as Tycho Brahe's assistant until the latter's death in 1601 and was then appointed Tycho's successor as Imperial Mathematician, the most prestigious appointment in mathematics in Europe. He occupied this post until, in 1612, Emperor Rudolph II was deposed. In Prague Kepler published a number of important books. In 1604 Astronomia pars Optica ("The Optical Part of Astronomy") appeared, in which he treated atmospheric refraction but also treated lenses and gave the modern explanation of the workings of the eye; in 1606 he published appeared in 1604; and in 1609 his De Stella Nova ("Concerning the New Star") on the new star that had Astronomia Nova ("New Astronomy") appeared, which contained his rst two laws (planets move in elliptical orbits with the sun as one of the foci, and a planet sweeps out equal areas in equal times). Whereas other astronomers still followed the ancient precept that the study of the planets is a problem only in kinematics, Kepler took an openly dynamic approach, introducing physics into the heavens. In 1610 Kepler heard and read about Galileo's discoveries with the spyglass. a long letter of support which he published as Dissertatio cum Nuncio Sidereo He quickly composed ("Conversation with the Sidereal Messenger"), and when, later that year, he obtained the use of a suitable telescope, he published his observations of Jupiter's satellites (Chapter 6) under the title Satellitibus ("Narration about Four Satellites of Jupiter observed"). Narratio de Observatis Quatuor Jovis These tracts were an enormous support to Galileo, whose discoveries were doubted or denied by many. Both of Kepler's tracts were quickly reprinted in Florence. Kepler went on to provide the beginning of a theory of the telescope in his Dioptrice, published in 1611. During this period the Keplers had three children (two had been born in Graz but died within months), Susanna (1602), who married Kepler's assistant Jakob Bartsch in 1630, Friedrich (1604-1611), and Ludwig (1607-1663). Kepler's wife, Barbara, died in 1612. In that year Kepler accepted the position of district mathematician in the city of Linz, a position he occupied until 1626. In Linz Kepler married Susanna Reuttinger. The couple had six children, of whom three died very early. In Linz Kepler published rst a work on chronology and the year of Jesus's birth, In German in 1613 and De Vero Anno quo Aeternus Dei Filius Humanam Naturam in Utero Benedictae Virginis Mariae Assumpsit (Concerning the True Year in which the Son of God assumed a Human Nature in more amply in Latin in 1614: the Uterus of the Blessed Virgin Mary"). In this work Kepler demonstrated 0 Kepler heard and read about Galileo's discoveries with the spyglass. He quickly composed a long letter of support which he published as Dissertatio cum Nuncio Sidereo ("Conversation with the Sidereal Messenger"), and when, later that year, he obtained the use of a suitable telescope, he published his observations of Jupiter's satellites under the title Narratio de Observatis Quatuor Jovis Satellitibus ("Narration about Four Satellites of Jupiter observed"). These tracts were an enormous support to Galileo, whose discoveries were doubted or denied by many. Both of Kepler's tracts were quickly reprinted in Florence. Kepler went on to provide the beginning of a theory of the telescope in his Dioptrice, published in 1611.that the Christian calendar was in error by ve years, and that Jesus had been born in 4 BC, a conclusion that is now universally accepted. Between 1617 and 1621 Kepler published Epitome Astronomiae Copernicanae ("Epitome of Copernican Astronomy"), which became the most inuential introduction to heliocentric astronomy; in 1619 he published Harmonice Mundi ("Harmony of the World"), in which he derived the heliocentric distances of the planets and their periods from considerations of musical harmony. In this work we nd his third law, relating the periods of the planets to their mean orbital radii. In 1615-16 there was a witch hunt in Kepler's native region, and his own mother was accused of being a witch. It was not until late in 1620 that the proceedings against her ended with her being set free. At her trial, her defense was conducted by her son Johannes. 1618 marked the beginning of the Thirty Years War, a war that devastated the German and Austrian region. Kepler's position in Linz now became progressively worse, as Counter Reformation measures put pressure on Protestants in the Upper Austria province of which Linz was the capital. Because he was a court ocial, Kepler was exempted from a decree that banished all Protestants from the province, but he nevertheless suered persecution. During this time Kepler was having his Available for free at Connexions <http://cnx.org/content/col10432/1.1> Tabulae Rudolphinae 21 ("Rudolphine Tables") printed, the new tables, based on Tycho Brahe's accurate observations, calculated according to Kepler's elliptical astronomy. When a peasant rebellion broke out and Linz was besieged, a re destroyed the printer's house and shop, and with it much of the printed edition. Soldiers were garrisoned in Kepler's house. He and his family left Linz in 1626. The Tabulae Rudolphinae were published in Ulm in 1627. Kepler now had no position and no salary. He tried to obtain appointments from various courts and returned to Prague in an eort to pry salary that was owed him from his years as Imperial Mathematician from the imperial treasury. He died in Regensburg in 1630. Besides the works mentioned here, Kepler published numerous smaller works on a variety of subjects. Available for free at Connexions <http://cnx.org/content/col10432/1.1> 22 CHAPTER 4. JOHANNES KEPLER Available for free at Connexions <http://cnx.org/content/col10432/1.1> Chapter 5 1 Ptolemaic System Figure 5.1: In his Ptolemaic System Dialogue Concerning the Two Chief World Systems, Ptolemaic and Copernican of 1632, Galileo attacked the world system based on the cosmology of Aristotle (384-322 BCE) and the technical astronomy of Ptolemy (ca. 150 CE). In his books On the Heavens, and Physics, Aristotle put forward his notion of an ordered universe or cosmos. It was governed by the concept of place , as opposed to space, and was divided into two distinct parts, the earthly or sublunary region, and the heavens. The former was the abode of change and corruption, where things came into being, grew, matured, decayed, and died; the latter was the region of perfection, where there was no change. In the sublunary region, substances were made up of the four elements, earth, 1 This content is available online at <http://cnx.org/content/m11943/1.3/>. Available for free at Connexions <http://cnx.org/content/col10432/1.1> 23 CHAPTER 5. PTOLEMAIC SYSTEM 24 water, air, and re. Earth was the heaviest, and its natural place was the center of the cosmos; for that reason the Earth was situated in the center of the cosmos. The natural places of water, air, and re, were concentric spherical shells around the sphere of earth. Things were not arranged perfectly, and therefore areas of land protruded above the water. Objects sought the natural place of the element that predominated in them. Thus stones, in which earth predominated, move down to the center of the cosmos, and re moves straight up. Natural motions were, then, radial, either down or up. The four elements diered from each other only in their qualities. Thus, earth was cold and dry while air was warm and moist. Changing one or both of its qualities, transmuted one element into another. Such transmutations were going on constantly, adding to the constant change in this sublunary region. Figure 5.2: Ptolemy The heavens, on the other hand, were made up of an entirely dierent substance, the aether quintessence (fth element), an immutable substance. 2 The 2 or Heavenly bodies were part of spherical shells of traditional English spelling, aether, is used here to distinguish Aristotle's heavenly substance from the modern chemical Available for free at Connexions <http://cnx.org/content/col10432/1.1> 25 aether. These spherical shells t tightly around each other, without any spaces between them, in the following order: Moon, Mercury, Venus, Sun, Mars, Jupiter, Saturn, xed stars. Each spherical shell (hereafter, simply, sphere) had its particular rotation, that accounted for the motion of the heavenly body contained in it. Outside the sphere of the xed stars, there was the prime mover (himself unmoved), who imparted motion from the outside inward. All motions in the cosmos came ultimately from this prime mover. The natural motions of heavenly bodies and their spheres was perfectly circular, that is, circular and neither speeding up nor slowing down. It is to be noted about this universe that everything had its natural place, a privileged location for bodies with a particular makeup, and that the laws of nature were not the same in the heavenly and the earthly regions. Further, there were no empty places or vacua anywhere. Finally, it was nite: beyond the sphere of the xed stars and the prime mover, there was nothing, not even space. The cosmos encompassed all existence. Figure 5.3: Christian Aristotelian Cosmos. From Peter Apian, Cosmographia3 Now, ingenious as this cosmology was, it turned out to be unsatisfactory for astronomy. Heavenly bodies did, in fact, not move with perfect circular motions: they speeded up, slowed down, and in the cases of the planets even stopped and reversed their motions. Although Aristotle and his contemporaries tried to account for these variations by splitting individual planetary spheres into component spheres, each with a component of the composite motion, these constructions were very complex and ultimately doomed to failure. Furthermore, no matter how complex a system of spheres for an individual planet became, these spheres were still centered on the Earth. The distance of a planet from the Earth could therefore not be varied in this system, but planets vary in brightness, a variation especially noticeable for Venus, Mars, and Jupiter. Since in an unchangeable heaven variations in intrinsic brightness were ruled out, and since spheres did not allow for a variation in planetary distances from the Earth, variations in brightness could not be accounted for in this system. Thus, although Aristotle's spherical cosmology had a very long life, mathematicians who wished to make geometrical models to account for the actual motions of heavenly bodies began using dierent constructions within a century of Aristotle's death. These constructions violated Aristotle's physical and cosmological principles somewhat, but they were ultimately successful in accounting for the motions of heavenly bodies. It is in the work of Claudius Ptolemy, who lived in the second century CE, that we see the culmination of these eorts. In his great astronomical work, Almagest, 4 Ptolemy presented a complete system of mathematical substance, ether. 3 http://cnx.org/content/m11943/latest/ptolematic_universe.gif 4 The title is one given to this book by Islamic translators in the ninth century. Its original Greek title is Mathematical Syntaxis. Available for free at Connexions <http://cnx.org/content/col10432/1.1> CHAPTER 5. PTOLEMAIC SYSTEM 26 constructions that accounted successfully for the observed motion of each heavenly body. Ptolemy used three basic constructions, the eccentric, the epicycle, and the equant. An eccentric construction is one in which the Earth is placed outside the center of the geometrical construction. Here, the Earth, E, is displaced slightly from the center, C, of the path of the planet. Although this construction violated the rule that the Earth was the center of the cosmos and all planetary motions, the displacement was minimal and was considered a slight bending of the rule rather than a violation. The eccentric in the gure below is xed; it could also be made movable. In this case the center of the large circle was a point that rotated around the Earth in a small circle centered on the Earth. In some constructions this little circle was not centered in the Earth. The second construction, the epicycle, is geometrically equivalent to the simple movable eccentric. In this case, the planet moved on a little circle the center of which rotated on the circumference of the large circle centered on the on theEarth. When the directions and speeds of rotation of the epicycle and large circle were chosen appropriately, the planet, as seen from the Earth, would stop, reverse its course, and then move forward again. Thus the annual retrograde motion of the planets (caused, in heliocentric terms by the addition of the Earth's annual motion to the motion of the planet) could roughly be accounted for. (a) (b) (c) From Michael J. Crowe, Theories of the World from Antiquity to the Copernican Revolution. (a) Eccentric5 (b) Epicycle6 (c) Equant7 Figure 5.4: But these two constructions did not quite bring the resulting planetary motions within close agreement with the observed motions. Ptolemy therefore added yet a third construction, the equant. In this case, the center of construction of the large circle was separated from the center of motion of a point on its circumference, as shown below, where C is the geometrical center of the large circle (usually called in these constructions the excentric circle) but the motion of the center of the epicycle, P (middle of Figure 5.4), is uniform about Q, the equant point (righthand side of Figure 5.4). Ptolemy combined all three constructions in the models of the planets, Sun, and Moon. A typical construction might thus be as in the picture below, where E is the Earth, C the geometric center of the eccentric circle, Q the equant point, F the center of the epicycle, and P the planet. As mentioned before, the eccentric was often not xed but moved in a circle about the Earth or another point between the Earth and the equant point. 5 http://cnx.org/content/m11943/latest/eccentric_p.gif 6 http://cnx.org/content/m11943/latest/epicycle_p.gif 7 http://cnx.org/content/m11943/latest/equant_p.gif Available for free at Connexions <http://cnx.org/content/col10432/1.1> 27 Typical Ptolemaic planetary model (From Michael J. Crowe, Theories of the World from Antiquity to the Copernican Revolution.)8 Figure 5.5: With such combinations of constructions, Ptolemy was able to account for the motions of heavenly bodies within the standards of observational accuracy of his day. The idea was to break down the complex observed planetary motion into components with perfect circular motions. In doing so, however, Ptolemy violated the cosmological and physical rules of Aristotle. The excentric and epicycle meant that planetary motions were not exactly centered on the Earth, the center of the cosmos. This was, however, a "fudge" that few objected to. The equant violated the stricture of perfect circular motion, and this violation bothered thinkers a good deal more. Thus, in De Revolutionibus (see Copernican System (Chapter 2)), Copernicus tells the reader that it was his aim to rid the models of heavenly motions of this monstrous construction. Aristotelian cosmology and Ptolemaic astronomy entered the West, in the twelfth and thirteenth centuries, as distinct textual traditions. The former in Aristotle's commentaries on these works; the latter in the Almagest Physics and On the Heavens and the many and the technical astronomical literature that had grown around it, especially the work of Islamic astronomers working in the Ptolemaic paradigm. In the world of learning in the Christian West (settled in the universities founded around 1200 CE), Aristotle's cosmology gured in all questions concerned with the nature of the universe and impinged on many philosophical and theological questions. Ptolemy's astronomy was taught as part of the undergraduate mathematical curriculum only and impinged only on technical questions of calendrics, positional predictions, and astrology. Copernicus's innovations was therefore not only putting the Sun in the center of the universe and working out a complete astronomical system on this basis of this premise, but also trying to erase the disciplinary boundary between the textual traditions of physical cosmology and technical astronomy. 8 http://cnx.org/content/m11943/latest/combined_p.gif Available for free at Connexions <http://cnx.org/content/col10432/1.1> 28 CHAPTER 5. PTOLEMAIC SYSTEM Available for free at Connexions <http://cnx.org/content/col10432/1.1> Chapter 6 Satellites of Jupiter Figure 6.1: 1 Jupiter's moons Jupiter has a large number of satellites. Of these, four are comparable to the Earth's Moon in size; the rest are orders of magnitude smaller. When Jupiter is at opposition and closest to the Earth, the stellar 2 magnitude of its four large moons is between 5 and 6. This means that, were it not for the shielding brightness of Jupiter, these bodies would be visible with the naked eye. The aperture of the telescope used by Galileo in 1610 and its magnication thus brought these four "Galilean" satellites within his grasp. But rst Galileo had to make adjustments to the instruments. When viewing bodies that are very bright and very small, the optical defects of the telescope (Chapter 3) can be crippling. By trial and error Galileo learned to stop down the aperture of his instrument until he could begin to make useful observations. At the end of 1609, as he was nishing his series of observations of the Moon (Chapter 10), Jupiter was at opposition and the brightest object in the evening sky (not counting the Moon). When he had made the new adjustment to his instrument, he turned his attention to Jupiter. On 7 January 1610 he observed the 1 This content 2 In Antiquity is available online at <http://cnx.org/content/m11971/1.2/>. a rough numerical brightness rating for stars and planets was developed. Stars of the rst magnitude were brightest; the dimmest celestial objects visible (to the naked eye) were assigned the sixth magnitude. This system is the basis of the modern system of stellar magnitudes bases on instrumental readings. Available for free at Connexions <http://cnx.org/content/col10432/1.1> 29 CHAPTER 6. SATELLITES OF JUPITER 30 planet and saw what he thought were three xed stars near it, strung out on a line through the planet. This formation caught his attention, and he returned to it the following evening. Galileo's expectation was that Jupiter, which was then in its retrograde loop, 3 would have moved from east to west and had left the three little stars behind. Instead, he saw all three stars to the west of Jupiter. It appeared as though Jupiter had not moved to the west but rather to the east. This was an anomaly, and Galileo returned to this formation again and again. Over the next week he found out several things. First, the little stars never left Jupiter; they appeared to be carried along with the planet. Second, as they were carried along, they changed their position with respect to each other and Jupiter. Third, there were not three but four of these little stars. By the 15th of January he had gured it out: these were not xed stars but rather planetary bodies that revolved around Jupiter. Jupiter had four moons. His book, Sidereus Nuncius, in which his discovery was described, came o the press in Venice in the middle of March 1610 and made Galileo famous. (a) Figure 6.2: (b) Galileo's observations of Jupiter's moon (a) large version4 (b) large version5 The moons of Jupiter had a major impact on cosmology. In 1610 the traditional Aristotelian cosmology had come under attacks from Copernican astronomers. Aristotelians had a number of arguments against the Copernican System (Chapter 2), one of which was now made obsolete. In traditional cosmology, there was only one center of motion, the center of the universe which was the place of the Earth. The motions of all heavenly bodies centered on the Earth. But according to the Copernican theory, the Earth went around the Sun while the Moon went around the Earth. There were thus two centers of motion, which seemed an absurdity. Moreover, if the Earth was a planet, like Mercury, Venus, Mars, Jupiter, and Saturn, why was it the only planet to have a Moon? Galileo's discovery answered this question. The Earth was, in fact, not the only planet to have a moon, Jupiter had four. And no matter what cosmological system one believed in, there were now at least two centers of motion in the universe, the Earth or Sun and Jupiter. Thus, although the satellites (the term was rst used by Johannes Kepler (Chapter 4)) of Jupiter were by no means proof of the truth of the Copernican system, they certainly added ammunition on that side of the argument. 3 When Jupiter is near opposition, it is on the same side of the Sun as the Earth, but the Earth is moving much faster than Jupiter. It therefore appears that Jupiter is moving backward with respect to the xed stars. 4 http://cnx.org/content/m11971/latest/journal_jup1.gif 5 http://cnx.org/content/m11971/latest/journal_jup2.gif Available for free at Connexions <http://cnx.org/content/col10432/1.1> 31 In the purely astronomical realm, the satellites of Jupiter posed a new problem for astronomers. It had taken centuries in Antiquity to arrive at adequate geometrical modes for the motions of the known planets. Now there was a new system of planetary bodies in miniature, and astronomers had to develop models that could predict their motions. There was a great incentive to come up with good mathematical models, for 6 the satellites oered some hope for the solution of the problem of longitude at sea . It took almost two centuries, however, before the models and tables based on them reached satisfactory accuracy. The naming of the satellites provides an interesting example of how such matters were handled before the foundation of the International Astronomical Union in the twentieth century. As their discoverer, Galileo claimed the right to name the satellites. He wanted to name them after his patrons and asked whether they 7 would prefer "Cosmic Stars" (after Cosimo II ) or "Medicean Stars." They opted for the latter, and through much of the seventeenth century they were known by that name. In his notebooks, Galileo referred to them individually by number, starting with the satellite closest to Jupiter, but he never had occasion to refer to them in this way in print. In Provence, Nicholas Claude Fabri de Peiresc tried to dierentiate between the Medicean Stars by assigning them the names of individual members of the family, but this system was not published and thus was never used by others. In his Mundus Iovialis ("Jovian World") of 1614, Simon Marius naming problem in some depth. 8 went into the First, he himself used the numerical system beginning with the satellite closest to Jupiter. Second, he thought that he might call them after his patron, the Duke of Brandenburg a suggestion followed by no one. Third, he suggested naming the farthest satellite the Saturn of Jupiter, the next one the Jupiter of Jupiter, the third one the Venus of Jupiter, and the one nearest the planet the Mercury of Jupiter. This cumbersome system never caught on. Finally, Marius related a suggestion by Kepler (Chapter 4): Jupiter is much blamed by the poets on account of his irregular loves. Three maidens are especially mentioned as having been clandestinely courted by Jupiter with success. Io, daughter of the River, Inachus, Callisto of Lycaon, Europa of Agenor. Then there was Ganymede, the handsome son of King Tros, whom Jupiter, having taken the form of an eagle, transported to heaven on his back, as poets fabulously tell . . . . I think, therefore, that I shall not have done amiss if the First is called by me Io, the Second Europa, the Third, on account of its majesty of light, Ganymede, the Fourth Callisto . . . . This fancy, and the particular names given, were suggested to me by Kepler, Imperial Astronomer, when we met at Ratisbon fair in October 1613. So if, as a jest, and in memory of our friendship then begun, I hail him as joint father of these four stars, again I shall not be doing wrong. [3] None of these suggestion caught on because with Jupiter's satellites, there was no confusion in the numbering system. Following Galileo and Marius, astronomers simply referred to them by number. With the satellites of Saturn, however, a problem developed. In 1655 Huygens discovered the rst and largest; then in 1671-72 Giandomenico Cassini discovered two more, and in 1684 yet another two. These ve satellites were numbered like their Galilean counterparts. But when in 1789 William Herschel discovered two additional satellites internal to the rst, confusion followed. Did one now renumber them all (thus causing confusion for those who consulted older works), refer to the two new ones as nos. 6 and 7 (thus making the order of the satellites confusing), or refer to them by order of discovery (equally confusing as to order)? Herschel's son, John Frederick William, suggested in 1847 that Saturn's satellites be given individual names of mythological gures associated with Saturn after the suggestion made by Marius for Jupiter's satellites. When, the following year, William Lassel and George Bond independently discovered an eighth satellite of Saturn, they agreed to adopt the naming system proposed by Herschel, in which Saturn's satellites were named after his brothers and sisters, the Titans. This system and the now revived suggestion by Kepler and Marius for Jupiter quickly became the convention for naming the satellites of the superior planets. 6 "Longitude at Sea" <http://cnx.org/content/m11963/latest/> 7 "The Medici Family" <http://cnx.org/content/m11975/latest/> 8 "Simon Marius" <http://cnx.org/content/m11973/latest/> Available for free at Connexions <http://cnx.org/content/col10432/1.1> CHAPTER 6. SATELLITES OF JUPITER 32 Modern Images of the Galilean Satellites (a) (e) Figure 6.3: 16 (h) Callisto (b) (f) (c) (g) (d) (h) (a) Io9 (b) Io10 (c) Europa11 (d) Europa12 (e) Ganymede13 (f) Ganymede14 (g) Callisto15 9 http://cnx.org/content/m11971/latest/io1.gif 10 http://cnx.org/content/m11971/latest/io2.gif 11 http://cnx.org/content/m11971/latest/europa1.gif 12 http://cnx.org/content/m11971/latest/europa2.gif 13 http://cnx.org/content/m11971/latest/ganymede1.gif 14 http://cnx.org/content/m11971/latest/ganymede2.gif 15 http://cnx.org/content/m11971/latest/callisto1.gif 16 http://cnx.org/content/m11971/latest/callisto2.gif Available for free at Connexions <http://cnx.org/content/col10432/1.1> Chapter 7 Saturn Figure 7.1: 1 Saturn To all serious observers of the heaven, it was known that stars move in a xed formation around the Earth except for seven bodies that moved through the xed stars in a wide band, the zodiac. To the Greeks, all heavenly bodies were stars; most were xed but some wandered. These seven wandering stars, or planets, were (in the conventional order), Moon (Chapter 10), Mercury, Venus, Sun, Mars, Jupiter, Saturn. Mercury was the most dicult to observe because it was always close to the Sun, Venus, as morning or evening star, was the brightest body in the heavens. Mars had a distinctive red color, Jupiter at opposition was very bright, and the straw-colored Saturn, the slowest of all planets (sidereal period 30 years), was the dimmest. The planets were identied with gods by the Mesopotamians, and the Greeks copied this system, assigning planets the names of their gods. The planets were also associated with the seven known metals: Moon/silver, Mercury/mercury, Venus/copper, Sun/gold. Mars/iron, Jupiter/tin, and Saturn/lead. In accordance with their gods, the planets were assigned astrological meanings still used by the astrologers who write daily columns in many of our newspapers. 1 This content is available online at <http://cnx.org/content/m11972/1.2/>. Available for free at Connexions <http://cnx.org/content/col10432/1.1> 33 CHAPTER 7. SATURN 34 Figure 7.2: Saturn as the grim reaper2 Saturn, associated with time and the grim reaper, was usually depicted with a scythe. According to the prevailing cosmology of Aristotle, Western astronomers knew that, like all other heavenly bodies, the planet Saturn was perfect and spherical. The telescope therefore gave them a surprise. After publishing Sidereus Nuncius, in March 1610, Galileo continued scrutinizing the heavens, especially the planets, in the hope of 3 making further discoveries. In July, as Saturn was bright in the evening sky and approaching opposition, 4 he turned his telescope toward it and made a new discovery. On 30 July he wrote to his Medici patron: I discovered another very strange wonder, which I should like to make known to their Highnesses . . . , keeping it secret, however, until the time when my work is published . . . . the star of Saturn is not a single star, but is a compsite of three, which almost touch each other, never change or move relative to each other, and are arranged in a row along the zodiac, the middle one being three times larger than the lateral ones, and they are situated in this form: oOo. Galileo no doubt planned to publish this new discovery in his next book, but in the meantime, how could he preserve his priority and prevent others from claiming the discovery as their own? His solution was to circulate an anagram, s m a i s m r m i l m e p o e t a l e u m i b u n e n u g t t a u i r a s. Others would know that he had discovered something and when he had discovered it, but they would not known what the discovery was. The number of letters in the anagram, 37, was too small to allow him later to fudge and change the solution to describe a discovery made by someone else in the meantime. Before the days of scientic papers (invented in the 1660s) this was an eective (if not always foolproof ) method of claiming priority. Galileo sent his correspondents the solution of the anagram, Altissimum planetam tergeminum observavi, or "I have observed the highest planet tri-form." And the newly congured Saturn now took its place in Galileo's Hall of Fame. But there was something very strange about this planet. For one thing, after being notied other observers often saw the planet oval shaped, but Galileo argued that this was due to inferior telescopes. For another, if these lateral bodies were satellites, they were very dierent from the satellites of Jupiter for they were much larger with respect to the planet and never moved with respect to it. Or did they? 2 http://cnx.org/content/m11972/latest/saturn_manuscript-t.gif 3 At opposition, Saturn is 180 degrees removed from the Sun and crosses the meridian at midnight. It is then closest to the Earth and therefore at its brightest. 4 "The Medici Family" <http://cnx.org/content/m11975/latest/> Available for free at Connexions <http://cnx.org/content/col10432/1.1> 35 In his third sunspot (Chapter 8) letter, dated December 1612, Galileo revealed another mystery about the planet: the lateral bodies had disappeared. Although Galileo condently predicted that they would return, which they did, Saturn's appearances remained an enigma. If Saturn was sometimes seen oval (denied by Galileo), sometimes with two lateral bodies, and at other times round and solitary, how could one explain all these appearances? And the mystery grew deeper as time went on. In 1616 Galileo announced to his patrons that he had now observed Saturn in yet another shape, and he published this without commentary in his Asayer of 1623. (a) Figure 7.3: (b) Galileo's sketch of 1616 and engraving in The Assayer of 1623. Although the planet had again appeared solitary in 1626, few noticed this. But by the next solitary appearance in 1642, there was a growing community of telescopic astronomers who now made observation of the planet a central part of their research programs. Pierre Gassendi and Johannes Hevelius played central roles in this quest, but there were a number of others. Astronomers now routinely published gures of the shapes in which they had observed Saturn, a sampling of which can be seen in g. 3. Near the solitary appearances, virtually all astronomers still saw the planet triple-bodied as Galileo had rst seen it; at other times, however, they saw two arms, or handles (Latin, ansae) attached to the central body and, representations of this handled appearance varied greatly. Available for free at Connexions <http://cnx.org/content/col10432/1.1> CHAPTER 7. SATURN 36 Figure 7.4: The composite gure from Huygens's Systema Saturnium5 If in 1642 there was a lack of information about Saturn's appearances, by 1655 when the handles had again shrunk into little disks and the planet was approaching its solitary appearance, there was a plethora of information. What was needed now was a model or theory that would make sense out of all these divergent observations. In 1656 Hevelius pubished De Nativa Saturni Facie (On the Real Appearance of Saturn"), in which he proposed that Saturn's body was ellipsoidal in shape with two crescents attached to its extremeties. Rotation about the minor axis in the plane of the crescents would, according to Hevelius, explain all the planet's appearances. Figure 7.5: Hevelius's Theory6 5 http://cnx.org/content/m11972/latest/huygens_phases1.gif 6 http://cnx.org/content/m11972/latest/hevelius_phases.gif Available for free at Connexions <http://cnx.org/content/col10432/1.1> 37 His book convinced few. In 1658 Christopher Wren (remembered more for his later architecture) proposed a model in which a "corona" so thin it could be considered a mere surface was attached to the planet; the entire formation rotated or librated about its major axis. In the meantime, Christiaan Huygens had discovered a satellite of Saturn, now named Titan. In 1656 he published a brief tract on the discovery and included an anagram containing his own theory about Saturn's appearances. He unveiled his theory in 1659, in a substantial book entitled Systema Saturnium ("The Saturnian System"). Huygens's theory was that the planet was surrounded by a thin at ring that nowhere touched it. Although Huygens did think that the ring had an appreciable thickness, this was basically the modern solution of the problem. Figure 7.6: Wren's Theory7 But Huygens's solution was a geometrical one. The question now facing astronomers was how such a ring could be stable. Huygens thought the ring was a solid structure; others opined that it was made up of a huge swarm of minute satellites. The argument went on for several centuries until James Clerk Maxwell published his mathematical analysis of the ring structure in 1858, proving that the ring had to be made up of particles no larger than a few inches. At the end of the nineteenth century, spectrographic studies showed that the angular rotation of the inside of the ring was greater than that of the outside of the ring, and that the ratio obeyed Kepler's third law. The problem was now solved, although Saturn's ring system still held surprises, as can be seen from the results of the recent ybys of the planet. 7 http://cnx.org/content/m11972/latest/wren_phases.gif Available for free at Connexions <http://cnx.org/content/col10432/1.1> CHAPTER 7. SATURN 38 Figure 7.7: Huygen's Theory8 8 http://cnx.org/content/m11972/latest/huygens_phases2.gif Available for free at Connexions <http://cnx.org/content/col10432/1.1> Chapter 8 Sunspots Figure 8.1: 1 The Sun2 Sunspots are dark areas of irregular shape on the surface of the Sun. Their short-term and long-term cyclical nature has been established in the past century. Spots are often big enough to be seen with the naked eye. While direct observation of the Sun in a clear sky is painful and dangerous, it is feasible when the Sun is close to the horizon or when it is covered by a thin veil of clouds or mist. Records of naked-eye sunspot observations in China go back to at least 28 BCE. In the West, the record is much more problematical. It is possible that the Greek philosopher Anaxagoras observed a spot in 467 BCE, and it appears that there are a few scattered mentions in the ancient literature as well. However, in the dominant Aristotelian cosmology, the heavens were thought to be perfect and unchanging. A spot that comes and goes on the Sun would mean that there is change in the heavens. Given this theoretical predisposition, the diculty of observing the Sun, and the cyclic nature of spots, it is little wonder that records of sunspots are almost non-existent in Europe before the seventeenth century. A very large spot seen for no less than eight days in 807 was simply interpreted as a passage of Mercury in front of the Sun. Other mentions of spots seen on the Sun were ignored by the astronomers and philosophers. In 1607 Johannes Kepler (Chapter 4) wished to observe a predicted transit of Mercury across the Sun's disk, and on the appointed day he projected the Sun's image through a small hole in the roof of his house (a camera obscura) and did indeed observe a black spot that he interpreted to be Mercury. Had he been able to follow up on his observation the next day, he would still 1 This content is available online at <http://cnx.org/content/m11970/1.4/>. 2 http://cnx.org/content/m11970/latest/sun.gif Available for free at Connexions <http://cnx.org/content/col10432/1.1> 39 CHAPTER 8. SUNSPOTS 40 have seen the spot. Since he knew that Mercury takes only a few hours to cross the Sun's disk during one of its infrequent transits, he would have known that what he observed could not have been Mercury. Figure 8.2: A sunspot3 The scientic study of sunspots in the West began after the telescope had been brought into astronomy in 1609. Although there is still some controversy about when and by whom sunspots were rst observed through the telescope (Chapter 3), we can say that Galileo and Thomas Harriot 4 were the rst, around the 5 6 end of 1610; that Johannes and David Fabricius and Christoph Scheiner rst observed them in March 1611, and that Johannes Fabricius was the rst to publish on them. His book, De Maculis in Sole Observatis ("On the Spots Observed in the Sun") appeared in the autumn of 1611, but it remained unknown to the other observers for some time. Figure 8.3: Harriot's sunspot drawings.7 3 http://cnx.org/content/m11970/latest/ss_detailed.gif 4 "Thomas Harriot" <http://cnx.org/content/m11979/latest/> 5 "Johannes Fabricius" <http://cnx.org/content/m11961/latest/> 6 "Christoph Scheiner" <http://cnx.org/content/m12126/latest/> Available for free at Connexions <http://cnx.org/content/col10432/1.1> 41 In the meantime, Galileo had shown sunspots to a number of people in Rome during his triumphant visit there in the spring of 1611. But although some of his corespondents began making regular observations a few months later, Galileo himself did not undertake a study of sunspots until April 1612. Scheiner began his serious study of spots in October 1611 and his rst tract on the subject, Tres Epistolae de Maculis Solaribus Scriptae ad Marcum Welserum ("Three Letters on Solar Spots written to Marc Welser8 ") appeared in January 1612 under the pseudonym "Apelles latens post tabulam," or "Apelles waiting behind the painting." 9 Welser was a scholar and banker in Augsburg, who was a patron of local scholars. Figure 8.4: Sunspot plate from Scheiner's Tres Epistolae.10 Scheiner, a Jesuit mathematician at the university of Ingolstadt (near Augsburg), wished to preserve the perfection of the Sun and the heavens and therefore argued that sunspots were satellites of the Sun. They appeared as black spots when they passed in front of the Sun but were invisible at other points in their orbits. Their orbits had to be very close to the Sun for their shapes were foreshortened as they approached its edge. Scheiner observed sunspots through a telescope equipped with colored glasses. In the winter of 1611-12, when Galileo received a copy of Scheiner's tract from Welser along with a request for his comments, he was ill, and what little energy he had he was devoting to the publication of his Discourse on Bodies in Water. When, however, that book was at the printer's, in April 1612, he turned his 11 , who was in Florence12 at the time. attention to sunspots with the help of his protege Benedetto Castelli It was Castelli who developed the method of projecting the Sun's image through the telescope, a technique that made it possible to study the Sun in detail even when it was high in the sky. Galileo wrote his rst letter to Welser on sunspots, in which he argued that spots were, in fact, on the surface of the Sun or in its atmosphere, and although he could not say for certain what they were, they appeared to him most like clouds. While Scheiner wrote in Latin, Galileo wrote his letter in Italian, and Welser had to have it translated 7 http://cnx.org/content/m11970/latest/harriot_ss1.gif 8 "Marc Welser" <http://cnx.org/content/m11964/latest/> 9 Legend has it that the famous Greek painter Apelles once hid behind one of his painting to hear what people said about it. When a shoemaker praised the way Apelles had rendered shoes in the painting, Apelles revealed himself and thanked the shoemaker for the compliment, but this man now proceeded to give his not so complimentary opinions about other aspects of the painting. Apelles answered "Let the shoemaker stick to his last." 10 http://cnx.org/content/m11970/latest/tres_epistolae.gif 11 "Benedetto Castelli" <http://cnx.org/content/m11957/latest/> 12 "Florence and Tuscany" <http://cnx.org/content/m11936/latest/> Available for free at Connexions <http://cnx.org/content/col10432/1.1> CHAPTER 8. SUNSPOTS 42 before Scheiner could read it. Scheiner had continued his solar observations, and by the time he had mastered Galileo's letter he had already nished two more letters of his own to Welser. He now added a third, in which he commented that his observations agreed precisely with those of Galileo and defended his judgment that sunspots were solar satellites. This second series of letters was published by Welser in October 1612 under the title De Maculis Solaribus . . . Accuratior Disquisitio ("A More Accurate Disquisition . . . on Sunspots"). Scheiner maintained his pseudonym of Apelles "or, if you prefer, Odysseus under the shield of Ajax." In the meantime, Galileo had written a second letter to Welser in August 1612. In this letter he showed a large number of sunspot observations, made at roughly the same time of the day, so that the Sun's orientation was the same and the motion of the spots across its disk could be easily followed. Upon receiving Scheiner's second tract he wrote yet a third, dated December 1612, attacking Apelles's opinions once again. At the end of his last letter Galileo mentioned the Copernican System (Chapter 2) favorably in a way that some scholars have interpreted as his rst endorsement of that theory. Figure 8.5: "Helioscopium" used by Scheiner for his later sunspot observations.13 Galileo's three letters were published in Rome by the Lyncean Academy 14 in the summer of 1613. About a third of the copies had reprints of the two tracts by Apelles (whose identity had in the meantime become known) in their original Latin. There was little doubt about the winner of this contest. Scheiner's language was convoluted, and not only did Galileo demolish his argument, he also criticized Scheiner's a priori method of argument: the Sun is perfect, therefore it cannot have spots on its surface. Up to this point, relations between Galileo and Scheiner were not strained. Scheiner had treated Galileo with great respect, and Galileo had been courteous in his language. Ten years later, in his Assayer, Galileo complained about those who would steal his priority of discovery, mentioning the case of sunspots but not mentioning Scheiner. It is almost certain that Galileo was complaining about several others who had published on sunspots but who had not recognized his priority. Scheiner, who at this time was settling in Rome, took Galileo's complaint to be directed at him and became Galileo's sworn enemy. 13 http://cnx.org/content/m11970/latest/helioscopium.gif 14 "Accademia dei Lincei" <http://cnx.org/content/m11955/latest/> Available for free at Connexions <http://cnx.org/content/col10432/1.1> 43 (a) (b) (c) Sunspot drawings from Scheiner's Rosa Ursina. (a) large version15 (b) large version16 (c) large version17 Figure 8.6: 15 http://cnx.org/content/m11970/latest/scheiner_rosa_ursina1-l.gif 16 http://cnx.org/content/m11970/latest/scheiner_rosa_ursina2-l.gif 17 http://cnx.org/content/m11970/latest/scheiner_rosa_ursina3-l.gif Available for free at Connexions <http://cnx.org/content/col10432/1.1> CHAPTER 8. SUNSPOTS 44 Scheiner had in the meantime published several important books on optics, and he had continued his 18 which study of the Sun. He published his results in a massive tome, Rosa Ursina, ("The Rose of Orsini"), became the standard treatise on sunspots for over a century. Scheiner had abandoned his opinion that spots were solar satellites, and he indeed came out in favor of the system of Tycho Brahe 19 and abandoned the perfection of the heavens. His method of illustrating the motion of individual spots across the face of the Sun became the standard way of rendering this motion and the changing shapes of the spots. Figure 8.7: Sunspot drawing by Gassendi20 After this time, however, sunspot activity was drastically reduced. When, in 1671, a prominent sunspot was observed, it was treated as a rare event. Sunspot activity increased again after about 1710. The period of low activity is now referred to as the Maunder Minimum, after Edward Walter Maunder (1851-1928), one of the rst modern astronomers to study the long-term cycles of sunspots. Modern studies of sunspots originated with the rise of astrophysics, around the turn of the century. The chief early investigator of these phenomena in the United States was George Ellery Hale (1868-1938), who built the rst spectro-heliograph and built the Yerkes and Mount Wilson observatories, including the 200-inch telescope on Palomar Mountain. 18 The rose refers to the Sun, Cardinal Orsini was his patron who 19 "Tycho Brahe" <http://cnx.org/content/m11946/latest/> 20 http://cnx.org/content/m11970/latest/gassendi_ss.gif paid for the printing. Available for free at Connexions <http://cnx.org/content/col10432/1.1> 45 (a) Figure 8.8: (b) Sunspots drawings by Hevelius (a) large version21 (b) large version22 21 http://cnx.org/content/m11970/latest/hevelius_ss1.bmp 22 http://cnx.org/content/m11970/latest/hevelius_ss2.bmp Available for free at Connexions <http://cnx.org/content/col10432/1.1> 46 CHAPTER 8. SUNSPOTS Available for free at Connexions <http://cnx.org/content/col10432/1.1> Chapter 9 1 The Biography of Galileo Galilei 9.1 Galileo's Early Life Galileo was born in Pisa, Italy 2 on February 15, 1564. Galileo's mother was Giulia degli Ammannati. 3 His father, Vincenzo Galilei , was a musician. Galileo was the rst of six (though some people believe seven) children. His family belonged to the nobility but was not rich. In the early 1570's, he and his family 4 moved to Florence . 9.2 The Pendelum n 1581, Galileo began studying at the University of Pisa, where his father hoped he would study medicine. While at the University of Pisa, Galileo began his study of the pendulum 5 while, according to legend, he watched a suspended lamp swing back and forth in the cathedral of Pisa. However, it was not until 1602 that Galileo made his most notable discovery about the pendulum - the period (the time in which a pendulum swings back and forth) does not depend on the arc of the swing (the isochronism). Eventually, this discovery would lead to Galileo's further study of time intervals and the development of his idea for a pendulum clock. 9.3 On Motion In 1581, Galileo began studying at the University of Pisa, where his father hoped he would study medicine. While at the University of Pisa, Galileo began his study of the pendulum while, according to legend, he watched a suspended lamp swing back and forth in the cathedral of Pisa. However, it was not until 1602 that Galileo made his most notable discovery about the pendulum - the period (the time in which a pendulum swings back and forth) does not depend on the arc of the swing (the isochronism). Eventually, this discovery would lead to Galileo's further study of time intervals and the development of his idea for a pendulum clock. 9.4 Mechanical Devices In 1592, Galileo was appointed professor of mathematics at the University of Padua. While teaching there, he frequently visited a place called the Arsenal, where Venetian ships were docked and loaded. Galileo had always been interested in mechanical devices. Naturally, during his visits to the Arsenal, he became 1 This content is available online at <http://cnx.org/content/m11933/1.4/>. 2 "Italy" <http://cnx.org/content/m11960/latest/> 3 "Vincenzo Galileo" <http://cnx.org/content/m11934/latest/> 4 "Florence and Tuscany" <http://cnx.org/content/m11936/latest/> 5 "Galileo and the Pendulum" <http://cnx.org/content/m11929/latest/> Available for free at Connexions <http://cnx.org/content/col10432/1.1> 47 CHAPTER 9. THE BIOGRAPHY OF GALILEO GALILEI 48 fascinated by nautical technologies, such as the sector 6 and shipbuilding. In 1593, he was presented with the problem involving the placement of oars in galleys. He treated the oar as a lever and correctly made the 7 water the fulcrum. A year later, he patented a model for a pump . His pump was a device that raised water by using only one horse. 9.5 Family Life Galileo was never married. 8 However, he did have a brief relationship with Marina Gamba , a woman he met on one of his many trips to Venice. Marina lived in Galileo's house in Padua where she bore him three children. His two daughters, Virginia and Livia, were both put in convents where they became, respectively, 9 and Sister Arcangela. In 1610, Galileo moved from Padua to Florence where he took 10 a position at the Court of the Medici family . He left his son, Vincenzio, with Marina Gamba in Padua. In Sister Maria Celeste 1613, Marina married Giovanni Bartoluzzi, and Vincenzio joined his father in Florence. 9.6 Telescope Galileo invented many mechanical devices other than the pump, such as the hydrostatic balance 11 . But perhaps his most famous invention was the telescope (Chapter 3). Galileo made his rst telescope in 1609, modeled after telescopes produced in other parts of Europe that could magnify objects three times. created a telescope later that same year that could magnify objects twenty times. He With this telescope, he was able to look at the moon (Chapter 10), discover the four satellites of Jupiter (Chapter 6), observe a supernova, verify the phases of Venus, and discover sunspots (Chapter 8). His discoveries proved the Copernican system (Chapter 2) which states that the earth and other plaqnets revolve around the sun. Prior to the Copernican system, it was held that the universe was geocentric, meaning the sun revolved around the earth. 9.7 The Inquisition Galileo's belief in the Copernican System (Chapter 2) eventually got him into trouble with the Catholic 12 was a permanent institution in the Catholic Church charged with the eradication of Church. The Inquisition heresies. A committee of consultants declared to the Inquisition that the Copernican proposition that the Sun is the center of the universe was a heresy. Because Galileo supported the Copernican system, he was warned 13 , under order of Pope Paul V, that he should not discuss or defend Copernican 14 that he could write about Copernican theory as theories. In 1624, Galileo was assured by Pope Urban VIII by Cardinal Bellarmine Dialogue Concerning the Two Chief World Systems, Galileo was called to Rome in 1633 to face the Inquisition again. long as he treated it as a mathematical proposition. However, with the printing of Galileo's book, Galileo was found guilty of heresy for his Dialogue, and was sent to his home near Florence where he was to be under house arrest for the remainder of his life. In 1638, the Inquisition allowed Galileo to move to his home in Florence, so that he could be closer to his doctors. By that time he was totally blind. In 1642, Galileo died at his home outside Florence. 6 "The Sector" <http://cnx.org/content/m11977/latest/> 7 "The Pump" <http://cnx.org/content/m11976/latest/> 8 "Marina Gamba" <http://cnx.org/content/m11942/latest/> 9 "Maria Celeste" <http://cnx.org/content/m11941/latest/> 10 "The Medici Family" <http://cnx.org/content/m11975/latest/> 11 "Hydrostatic Balance" <http://cnx.org/content/m12127/latest/> 12 "The Inquisition" <http://cnx.org/content/m11944/latest/> 13 "Robert Cardinal" <http://cnx.org/content/m11968/latest/> 14 "Urban VIII" <http://cnx.org/content/m11983/latest/> Available for free at Connexions <http://cnx.org/content/col10432/1.1> Chapter 10 The Moon Figure 10.1: 1 The Moon in Sidereus Nuncius Ignoring the occasional pre-telescopic appearance of exceptionally large sunspots (Chapter 8), the Moon is the only heavenly body which shows features to the naked eyethe Man in the Moon. These features are permanent, and it was therefore obvious that the Moon always keeps its same face turned to us (although there are minor perturbations that were not noticed until later). In the philosophy of Aristotle (384-322 BCE), these features presented somewhat of a problem. The heavens, starting at the Moon, were the realm of perfection, the sublunary region was the realm of change and corruption, and any resemblance between these regions was strictly ruled out. Aristotle himself suggested that the Moon partook perhaps of some contamination from the realm of corruption. Although Aristotle's natural philosophy was very inuential in the Greek world, it was not without competitors and skeptics. Thus, in his little book On the Face in the Moon's Orb, the Greek writer Plutarch (46-120 CE) expressed rather dierent views on the relationship between the Moon and Earth. He suggested that the Moon had deep recesses in which the light of the Sun did not reach and that the spots are nothing but the shadows of rivers or deep chasms. He also entertained the possibility that the Moon was inhabited. In the following century, the Greek satirist Lucian (120-180 CE) wrote of an imaginary trip to the Moon, which was inhabited, as were the Sun and Venus. The medieval followers of Aristotle, rst in the Islamic world and then in Christian Europe, tried to make sense of the lunar spots in Aristotelian terms. 1 This Various possibilities were entertained. content is available online at <http://cnx.org/content/m11945/1.4/>. Available for free at Connexions <http://cnx.org/content/col10432/1.1> 49 It had been CHAPTER 10. THE MOON 50 suggested already in Antiquity that the Moon was a perfect mirror and that its markings were reections of earthly features, but this explanation was easily dismissed because the face of the Moon never changes as it moves about the Earth. Perhaps there were vapors between the Sun and the Moon, so that the images were actually contained in the Sun's incident light and thus reected to the Earth. The explanation that nally became standard was that there were variations of "density" in the Moon that caused this otherwise perfectly spherical body to appear the way it does. The perfection of the Moon, and therefore the heavens, was thus preserved. It is a curious fact that although many symbolic images of the Moon survive in medieval and Renaissance works of art (usually a crescent), virtually no one bothered to represent the Moon with its spots the way it actually appeared. We only have a few rough sketches in the notebooks of Leonardo da Vinci (ca. 1500) 2 by the English physician William Gilbert3 . None of these drawings and a drawing of the naked-eye moon found its way into print until well after the telescope (Chapter 3) had come into astronomy. The telescope delivered the coup de grace to attempts to explain away the Moon's spots and to the perfection of the heavens in general. With his telescope, Galileo saw not only the "ancient" spots, but many smaller ones never seen before. In these smaller spots, he saw that the width of the dark lines dening them varied with the angle of solar illumination. He watched the dark lines change and he saw light spots in the unilluminated part of the Moon that gradually merged with the illuminated part as this part grew. The conclusion he drew was that the changing dark lines were shadows and that the lunar surface has mountains and valleys. The Moon was thus not spherical and hardly perfect. Figure 10.2: Galileo's wash drawings4 5 drew the Galileo was not the only observer of the Moon. Indeed, he was not the rst. Thomas Harriot rst telescopic representation of the Moon and observed our nearest neighbor for several years. His drawings, however, remained unpublished. Those who wished to defend the perfection of the heavens brought out the old argument about rarity and density. In the letter of the Collegio Romano 6 mathematicians to Cardinal Bellarmine7 of April 1611, 8 Christoph Clavius (74 years old) expressed a minority opinion: "But it appears to Father Clavius more probable that the surface is not uneven, but rather that the lunar body is not of uniform density and has denser and rarer parts, as are the ordinary spots seen with the natural sight."[?] The other three Jesuit 2 http://cnx.org/content/m11945/latest/gilbert_moon.gif 3 "William Gilbert" <http://cnx.org/content/m11985/latest/> 4 http://cnx.org/content/m11945/latest/g_moonwash.gif 5 "Thomas Harriot" <http://cnx.org/content/m11979/latest/> 6 "Collegio Romano" <http://cnx.org/content/m11939/latest/> 7 "Robert Cardinal" <http://cnx.org/content/m11968/latest/> 8 "Christopher Clavius" <http://cnx.org/content/m11958/latest/> Available for free at Connexions <http://cnx.org/content/col10432/1.1> 51 mathematicians on the faculty of the college, however, believed that the lunar surface was indeed uneven. In this case the opposition faded away over the next few years. Galileo wrote in a letter, 1610, that he would like to make a series of representations of the Moon showing its changing phases. Presumably his purpose was to show how the shadows of individual features changed with the illumination. It appears that he abandoned this plan when he saw that there was no need for such an ambitious and expensive project: even the Jesuit fathers in Rome were convinced that the Moon's surface was uneven. Indeed, Galileo never returned to the task of representing the Moon. (In the 1630s he did, however, observe lunar librations, which show that the Moon does not always keep exactly the same face turned toward the Earth.) Others did little better. Thomas Harriot 9 did make a rough map of the full Moon 10 but never published it. Representations by Christoph Scheiner , Giuseppe Biancani, and Charles Malapert were little more than diagrams, useful only for supporting the verbal argument that the Moon's surface is rough and uneven. These were, so to speak, generic moons, not portraits of our nearest neighbor. Figure 10.3: Sketches of the Moon by Scheiner11 (1614), Biancani12 (1620) and Malapert13 (1619) If early observations and representations of the Moon were designed to address the issue of its mountainous nature and anity with the Earth, by the 1630s the accent was shifting. The rough lunar surface was now accepted by astronomers and they turned their attention to how telescopic observations could help them solve the problem of longitude 14 . A lunar eclipse is an event that appears the same to all observers for whom the Moon is above the horizon (which is, of course, not the case with solar eclipses). As the Moon enters the Earth's shadow cone, one can mark the times at which the shadow crosses a particular feature and later compare this time with the (local) time at which a distant colleague observed the same event. The dierence 15 But a verbal description of the lunar in local times translates directly into their dierence in longitude. feature under consideration was not enough. A lunar map was needed on which specic features could be unambiguously identied. In Aix and Provence, Nicholas Claude Fabri de Peiresc (still interested in the problem of longitude) and his friend, the astronomer Pierre Gassendi, decided to make a moonmap. They engaged the services of Claude Mellan, one of the foremost artists and engravers of his age. With Gassendi's sketches and guidance, Mellan engraved three view of the Moon, rst quarter, full Moon, and last quarter. 9 "Thomas Harriot" <http://cnx.org/content/m11979/latest/> 10 "Christoph Scheiner" <http://cnx.org/content/m12126/latest/> 11 http://cnx.org/content/m11945/latest/scheinermoon.bmp 12 http://cnx.org/content/m11945/latest/biancanimoon.bmp 13 http://cnx.org/content/m11945/latest/malapertmoon.bmp 14 "Longitude at Sea" <http://cnx.org/content/m11963/latest/> 15 24 hours=360 ◦ . Available for free at Connexions <http://cnx.org/content/col10432/1.1> CHAPTER 10. THE MOON 52 Figure 10.4: Claude Mellan's moon engravings: 116 , 217 ,318 . Mellan's three engravings are surely the nest artistic renderings of the Moon ever made, but they show an artist's Moon, not an astronomer's Moon. Mellan wonderfully represented what he saw through the telescope: at rst and last quarter the details at the edge of the Moon are washed out while the features near the terminator stand out starkly; conversely, at full Moon the features in the center are washed out while those near the edge show prominent relief. Where the solar rays are perpendicular to the lunar surface they cast no shadows, but where they rake the surface they throw long shadows. What astronomers needed was a single map that showed all the features equally clearlya composite view that pictured the Moon in a way it never appeared in reality but was accurate in its placement of individual features. The rst such map was made by the Belgian cosmographer and astronomer Michael Florent van Langren in 1645. Two years later a much more inuential eort was published by Johannes Hevelius. In 1647 Hevelius, a wealthy brewer in the Polish city of Gdansk, published Selenographia, the rst treatise entirely devoted to the Moon. Hevelius combined all the talents necessary for his task. He made his own lenses, constructed his own telescopes, observed the Moon on every clear night for several years, drew his observations, engraved them himself, and had the wealth to publish a sumptuous book at his own expense. In Selenographia he presented engravings of every conceivable phase of the Moon as well as three large plates of the full Moon 19 : one of the ways the full Moon actually appeared through the telescope, one the way a maker of terrestrial maps might represent it (using the conventions of geographers), and one a composite map of all lunar features illuminated (impossibly) from the same side. It is this last map that was to be used by astronomers during lunar eclipses. Hevelius also suggested a system of nomenclature based on earthly features. Hevelius founded the science of selenography (after Selene, the goddess of the Moon) and showed astronomers how to represent heavenly bodies. Selenographia was a model for all who came after him. All lunar maps since his time have used the convention of single illumination (although while he used morning illumination modern maps use evening illumination after van Langren's model). He also instituted the practice of showing the entire lunar surface visible from the Earth, which, because of librations, is greater than a hemisphere. Hevelius's nomenclature, although used in Protestant countries until the eighteenth century, was replaced by the system published in 1651 by the Jesuit astronomer Giovanni Battista Riccioli, who gave the large naked-eye spots the names of seas (Sea of Tranquillity, Sea of Storm, etc.) and the telescopic spots (now called craters) the name of philosophers and astronomers (g. 18). It should be pointed out that although Riccioli wrote his Almagestum Novum ("New Almagest") in which this map appeared to combat the Copernican theory (Chapter 2), he was evenhanded in assigning names: Copernicus and Kepler were 16 http://cnx.org/content/m11945/latest/mellan.bmp 17 http://cnx.org/content/m11945/latest/mella2.bmp 18 http://cnx.org/content/m11945/latest/mellan3.bmp 19 http://cnx.org/content/m11945/latest/hevelius_moon_r.gif Available for free at Connexions <http://cnx.org/content/col10432/1.1> 53 assigned prominent craters, and even Galileo received his due. One last note. As the astronomical telescope (Chapter 3) with its inverted image came into use, as- tronomers quickly adopted the habit of representing the way they saw the Moonupside down 20 . This practice was followed until very recently. Lunar images are now constructed and stored digitally and can be displayed in any orientation. Astronomers have therefore reverted to showing the Moon right side up. 20 http://cnx.org/content/m11945/latest/cassini_moon.gif Available for free at Connexions <http://cnx.org/content/col10432/1.1> GLOSSARY 54 Glossary A the Church began a series of reform atmospheric refraction measures of their own. These reform The change in direction of a ray of light as measures aimed to keep Church members it passes from space into the atmosphere. from becoming Protestants, and were This causes celestial objects to appear to be in a location dierent from their actual ones. C known as the Counter Reformation. J camera obscura Jesuits - The popular name for the monastic order - A darkened boxlike device in which called the Society of Jesus. The order images of external objects, received was founded by Ignatius de Loyola in through an aperture, are exhibited in 1534, and was recognized by the pope in their natural colors on a surface arranged 1540. The mission of the Jesuits was in to receive them. three areas: teaching, service to the nobility, and missionary work in foreign Carmelite Order lands. Their greatest mark was made in The Brothers of the Blessed Virgin Mary education, and the Collegio Romano was of Mount Carmel is one of the mendicant their primary seminary. orders originating on Mount Carmel in Israel. L Counter Reformation - The real or apparent oscillatory motion of the moon. - As dissenting groups split o from the Catholic Church in what came to be known as the Protestant Reformation, the Church began a series of reform lunar librations P parallax The change in the position of an object in measures of their own. These reform the heavens due to the orbit of the earth. measures aimed to keep Church members Observable parallax in the xed stars is a from becoming Protestants, and were proof of the rotation of the earth around known as the Counter Reformation. the sun. See this explanatory diagram. Counter Reformation As dissenting groups split o from the Catholic Church in what came to be known as the Protestant Reformation, S sidereal period - A period determined by or from the stars. Available for free at Connexions <http://cnx.org/content/col10432/1.1> Bibliography [1] Aristotle. Physics and on the heavens. In Jonathan Barnes, editor, The Revised Oxford Translation. The Complete Works of Aristotle: Princeton University Press, Princeton, 1984. The Aristotelian cosmos is described. John Kepler. [2] Angus Armitage. [3] Caspar. Max. Kepler. Faber, London, 1966. Abelard Schuman, New York, 1959. Translated by C. Doris Hellman. [4] Nicholas Copernicus. On the revolutions. In tr. Edward Rosen, editor, Complete works. Macmillan, Lon- don, 1972-. one of two modern, reliable translations of De Revolutionibus; issued separately, Baltimore: Johns Hopkins Press, 1978. [5] Nicholas Copernicus. On the Revolutions of the Heavenly Spheres. David & Charles; Barnes & Noble, London; New York, 1976. A. M. Duncan, tr.; one of two modern, reliable translations of De Revolutionibus. Theories of the World from Antiquity to the Copernican Revolution. [6] Michael J. Crowe. Dover, New York, 1990. Good expositions of the technical details of the Ptolemaic System. [7] Susanne Debarbat and Curtis Wilson. and Bradley". "The Galilean Satellites of Jupiter from Galileo to Cassini, Romer Cambridge University Press, Cambridge, 1984. In The General History of Astronomy. 4 vols., edited by M. A. H oskin, IIA: 14 4-57. [8] Stillman Drake. Discoveries and Opinions of Galileo. [9] Stillman Drake. "sunspots, sizzi, and scheiner". Doubleday, Garden City, NY, 1957. alileo studies: Personality, Tradition, and Revolution, Ann Arbor: University of Michigan Press:177199, 1970. [10] Stillman Drake. Galileo's steps to full copernicanism and back, studies in history and philosophy of science. In Larry Laudan Arthur Donovan and Rachel Laudan, editors, Studies of Scientic Change, [11] J. V. Field. Scrutinizing Science: Empirical pages 93105. Dordrecht Kluwer, 1987. On Galileo's Copernicanism. Kepler's Geometrical Cosmology. University of Chicago Press, London: Athlone Press; Chicago, 1988. [12] Maurice A. Finocchiaro. Galileo's copernicanism and the acceptability of guiding assumptions. Larry Laudan Arthur Donovan and Rachel Laudan, editors, Scientic Change, pages 4967. Dordrecht Kluwer, 1988. On Galileo's Copernicanism. [13] Richard Fremantle. Dioptrics. In Scrutinizing Science: Empirical Studies of The Sidereal Messenger of Galileo Galilei: and a Part of the Preface to Kepler's Rivingtons, London, 1880. Translated by Edward Staord Carlos. [14] Richard Fremantle. Sidereus Nuncius, or the Sidereal Messenger. University of Chicago Press, Chicago, 1989. Translated by Albert Van Helden. Available for free at Connexions <http://cnx.org/content/col10432/1.1> 55 BIBLIOGRAPHY 56 [15] B. R. Goldstein and A. C. Bowen. A new view of early greek astronomy. Isis, 74:33040, 1983. On the relationship between Greek cosmology and astronomy. [16] Edward Grant. Cosmology. In David C. Lindberg, editor, Science in the Middle Ages, pages 265302. University of Chicago Press, Chicago, 1984. On Medieval cosmology and astronomy. [17] Fernand Hallyn. The Poetic Structure of the World: Copernicus and Kepler. Zone Books, New York, 1990. Translated by Donald M. Leslie. [18] Keith Hutchison. Keith. "sunspots, galileo, and the orbit of the earth". Isis, 81:6874, 1990. [19] Vincent Ilardi. Eyeglasses and concave lenses in fteenth-century orence and milan: New documents. Renaissance Quarterly, 29:341360, 1976. The Birth of History and Philosophy of Science: Kepler's A Defence of Tycho against [20] Nicholas Jardine. Ursus. The appearance of spectacles with concave lenses is discussed. Cambridge University Press, Cambridge, 1984. Joannis Kepleri Astronomi Opera Omnia. [21] Johannes Kepler. 1858-1871. 8 vols. Edited by C. Frisch. Frankfurt and Erlange. Johannes Kepler Gesammelte Werke. [22] Johannes Kepler. Beck, Munich, 1937-. Edited by Max Caspar et al. Epitome of Copernican Astronomy [books IV and V]; The Harmonies of the World [23] Johannes Kepler. [Book V]. Encyclop aedia Britannica, Chicago, 1955. Translated by Charles Glenn Wallis. In Great Books of the Western World. Vol. 16. [24] Johannes Kepler. Kepler's Conversation with Galileo's Sidereal Messenger. Johnson Reprint, New York, 1965. Translated by Edward Rosen. The Six-Cornered Snowake. [25] Johannes Kepler. Clarendon Press, Oxford, 1966. Translated by Colin Hardie. Somnium: the Dream, or Posthumous Work on Lunar Astronomy. [26] Johannes Kepler. University of Wisconsin Press, Madison, 1967. Translated by Edward Rosen. Mysterium CosmographicumThe Secret of the Universe. [27] Johannes Kepler. Abaris Books, New York, 1981. Translated by A. M. Duncan. New Astronomy. [28] Johannes Kepler. Cambridge University Press, Cambridge, 1992. Translated by William H. Donahue. [29] Henry King. The History of the Telescope. Grin, London, 1955. The most convenient source for information on the general development of the telescope. Johannes Kepler and Planetary Motion. [30] David C. Knight. [31] Arthur Koestler. Chatto and Windus, London, 1965. The Watershed: a Biography of Johannes Kepler. The Copernican Revolution. [32] Thomas S. Kuhn. Doubleday, Garden City, 1960. Harvard University Press, Cambridge, 1957. The best account of the Copernican revolution. [33] Thomas S. Kuhn. The Copernican Revolution. Harvard University Press, Cambridge, 1957. On the relationship between Greek cosmology and astronomy. [34] James M. Lattis. Cosmology. Between Copernicus and Galileo: Christoph Clavius and the Collapse of Ptolemaic University of Chicago Press, Chicago, 1994. For an account of Aristotelian cosmology and Ptolemaic astronomy in the period leading up to Galileo's discoveries. Available for free at Connexions <http://cnx.org/content/col10432/1.1> BIBLIOGRAPHY [35] Martha List. 57 Bibliographia Kepleriana. Second edition. Beck, Munich, 1968. Novelties in the Heavens: Rhetoric and Science in the Copernican Controversy. [36] Jean Dietz Moss. University of Chicago Press, Chicago, 1993. "Thomas Harriot and the First Telescopic Observations of Sunspots." In Thomas Harriot: Renaissance Scientist. Clarendon Press, Edited by John W. Shirley, pp. 129-165. Oxford, [37] John D. North. 1974. A Survey of the Almagest. [38] Olaf Pedersen. Odense University Press, Odense, 1974. Good expositions of the technical details of the Ptolemaic System. [39] Olaf Pedersen. Astronomy. In David C. Lindberg, editor, Science in the Middle Ages, pages 30337. University of Chicago Press, Chicago, 1984. On Medieval cosmology and astronomy. [40] Olaf Pedersen and Mogens Pihl. Early physics and astronomy : a historical introduction. MacDonald and Janes; American Elsevier, (London; New York, 1974. (2nd ed. Cambridge: Cambridge University Press, 1993) Good expositions of the technical details of the Ptolemaic System. [41] Edward Rosen. The invention of eyeglasses. Journal for the History of Medicine and Allied Sciences, 11:1346, 183218, 1956. For the invention of spectacles. [42] Edward Rosen. Copernicus and the Scientic Revolution. Krieger, Malabar, FL, 1984. a useful, if eccentric biography of Copernicus with a collection of documents concerning his life. [43] Edward Rosen. Three Imperial Mathematicians: Kepler Trapped Between Tycho Brahe and Ursus. Abaris Books, New York, 1986. [44] Kunitomo Sakurai. "the solar activity in the time of galileo". Journal for the History of Astronomy, 11:164173, 1980. [45] George Sarton. "early observations of sunspots?". [46] Justin D. Schove. Sunspots Cycles. Isis, 37:6971, 1947. Hutchinson Ross Stroudsburg, PA, 1983. [47] William R. Shea. "galileo, scheiner, and the interpretation of sunspots". [48] William R. Shea. Isis, 61:498519, 1970. Galileo's Intellectual Revolution: Middle Period (1610-1632). Science History Publi- cations, New York, 1972. [49] A. Mark. Smith. "galileo's proof for the earth's motion from the movement of sunspots". Isis, 76:543 551, 1985. [50] Bruce Stephenson. Kepler's Physical Astronomy. [51] tr. G. J. Toomer, editor. Ptolemy's Almagest. Springer Verlag, New York, 1987. Duckworth; Springer Verlag, 1984, London; New York. The best translation of the Almagest. [52] Albert Van Helden. "annulo cingitur: the solution of the problem of saturn". of Astronomy, Journal for the History 5:155174, 1974. [53] Albert Van Helden. "saturn and his anses". Journal for the History of Astronomy, [54] Albert van Helden. The `astronomical telescope,' 1611-165. Scienza di Firenze, 1(2):1336, 1976. 5:105121, 1974. Annali dell'Istituto e Museo di Storia della see also for discussion of the problem of the invention of the telescope. [55] Albert van Helden. Astronomy, The development of compound eyepieces, 1640-1670. Journal for the History of 8:2637, 1977. see also for discussion of the problem of the invention of the telescope. Available for free at Connexions <http://cnx.org/content/col10432/1.1> BIBLIOGRAPHY 58 [56] Albert van Helden. The invention of the telescope. Transactions of the American Philosophical Society, 67(4), 1977. The entire problem of the invention of the telescope is discussed. [57] Adriaan W. Vliegenthart. "galileo's sunspots: Their role in 17th-century allegorical thinking". Physis, 7:273280, 1965. [58] Robert S. Westman. and michael maestlin. Three responses to the copernican theory: In Robert S. Westman, editor, Johannes praetorius, tycho brahe, The Copernican Achievement, University of California Press, Berkeley and Los Angeles, 1975. pages 285345. For the dierent receptions of De Revolutionibus. Available for free at Connexions <http://cnx.org/content/col10432/1.1> INDEX 59 Index of Keywords and Terms Keywords are listed by the section with that keyword (page numbers are in parentheses). Keywords do not necessarily appear in the text of the page. They are merely associated with that section. apples, 1.1 (1) Terms are referenced by the page they appear on. A B C aerial telescopes, 14 atmospheric refraction, 4(17), 20 J Cardinal Bellarmine, 9(47) Carmelite, 2(3), 7 Christoph Clavius, 2(3), 10(49) Jupiter, 6(29) K L lenses, 10 longitude, 10(49) lunar librations, 10(49), 51 Copernican, 2(3), 4(17) Lyncean Academy, 8(39) M David Fabricius, 8(39) Marina Gamba, 9(47) Moon, 3(9), 6(29), 7(33), 9(47), 10(49) Cosimo II, 6(29) Counter Reformation, 2(3), 7, 4(17), 18, 20 Marc Welser, 8(39) Medici, 7(33), 9(47) Copernicus, 3(9) P De Motu, 9(47) myopia, 10 Paolo Antonio Foscarini, 2(3) parallax, 6 pendulum, 9(47) Europa, 6(29) Pope Urban VIII, 9(47) presbyopia, 10 Florence, 8(39), 9(47) Ptolemaic System, 5(23) Ptolemy, 2(3) Galiileo, 5(23) Galilei, 9(47) Galileo, 3(9), 4(17), 7(33), 8(39), 9(47), 10(49) Ganymede, 6(29) geocentric, 9(47) geocentric astronomy, 3(9) I Kepler, 4(17) longitude at sea, 6(29) Copernican theory, 10(49) H Jupiter's satellites, 4(17) Collegio Romano, 10(49) 9(47) E F G Johannes, 4(17) Christoph Scheiner, 8(39) Copernican System, 5(23), 6(29), 8(39), D Jesuit, 10(49), 50 8(39) Biography, 9(47) camera obscura, 8(39), 39 Giordano Bruno, 2(3) Hans Lipperhey, 3(9) hydrostatic balance, 9(47) Ex. apples, 1 Johannes Kepler, 2(3), 3(9), 6(29), Benedetto Castelli, 8(39) Callisto, 6(29) Ex. S pump, 9(47) Satellites, 6(29) satellites of Jupiter, 3(9), 9(47) Saturn, 7(33) Science, 3(9), 5(23) sector, 9(47) sidereal, 33 sidereal period, 7(33) Simon Marius, 6(29) Sister Maria Celeste, 9(47) Index of Forbidden Books, 2(3) sunspot, 7(33) Inquisition, 9(47) Sunspots, 8(39), 10(49) Io, 6(29) System, 2(3) Italy, 9(47) Available for free at Connexions <http://cnx.org/content/col10432/1.1> INDEX 60 T Telescope, 3(9), 6(29), 8(39), 10(49) Thomas Harriot, 8(39), 10(49) Tycho Brahe, 2(3), 4(17), 8(39) V W Vincenzo Galilei, 9(47) William Gilbert, 10(49) Available for free at Connexions <http://cnx.org/content/col10432/1.1> ATTRIBUTIONS 61 Attributions Collection: solar system Edited by: Joel Thierstein URL: http://cnx.org/content/col10432/1.1/ License: http://creativecommons.org/licenses/by/2.0/ Module: "Copernican System" By: Albert Van Helden URL: http://cnx.org/content/m11938/1.3/ Pages: 3-8 Copyright: Albert Van Helden License: http://creativecommons.org/licenses/by/1.0 Module: "Galileo's Telescope" By: Albert Van Helden URL: http://cnx.org/content/m11932/1.4/ Pages: 9-16 Copyright: Albert Van Helden License: http://creativecommons.org/licenses/by/1.0 Module: "Johannes Kepler" By: Albert Van Helden URL: http://cnx.org/content/m11962/1.2/ Pages: 17-21 Copyright: Albert Van Helden License: http://creativecommons.org/licenses/by/1.0 Module: "Ptolemaic System" By: Albert Van Helden URL: http://cnx.org/content/m11943/1.3/ Pages: 23-27 Copyright: Albert Van Helden License: http://creativecommons.org/licenses/by/1.0 Module: "Satellites of Jupiter" By: Albert Van Helden URL: http://cnx.org/content/m11971/1.2/ Pages: 29-32 Copyright: Albert Van Helden License: http://creativecommons.org/licenses/by/1.0 Module: "Saturn" By: Albert Van Helden URL: http://cnx.org/content/m11972/1.2/ Pages: 33-38 Copyright: Albert Van Helden License: http://creativecommons.org/licenses/by/1.0 Available for free at Connexions <http://cnx.org/content/col10432/1.1> ATTRIBUTIONS 62 Module: "Sunspots" By: Albert Van Helden URL: http://cnx.org/content/m11970/1.4/ Pages: 39-45 Copyright: Albert Van Helden License: http://creativecommons.org/licenses/by/1.0 Module: "The Biography of Galileo Galilei" By: Albert Van Helden URL: http://cnx.org/content/m11933/1.4/ Pages: 47-48 Copyright: Albert Van Helden License: http://creativecommons.org/licenses/by/1.0 Module: "The Moon" By: Albert Van Helden URL: http://cnx.org/content/m11945/1.4/ Pages: 49-53 Copyright: Albert Van Helden License: http://creativecommons.org/licenses/by/1.0 Available for free at Connexions <http://cnx.org/content/col10432/1.1> solar system this is a guide to the solar system. About Connexions Since 1999, Connexions has been pioneering a global system where anyone can create course materials and make them fully accessible and easily reusable free of charge. We are a Web-based authoring, teaching and learning environment open to anyone interested in education, including students, teachers, professors and lifelong learners. We connect ideas and facilitate educational communities. Connexions's modular, interactive courses are in use worldwide by universities, community colleges, K-12 schools, distance learners, and lifelong learners. Connexions materials are in many languages, including English, Spanish, Chinese, Japanese, Italian, Vietnamese, French, Portuguese, and Thai. Connexions is part of an exciting new information distribution system that allows for Print on Demand Books. Connexions has partnered with innovative on-demand publisher QOOP to accelerate the delivery of printed course materials and textbooks into classrooms worldwide at lower prices than traditional academic publishers.