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Ptolemaic System

Ptolemaic system

The Ptolemaic system was a model to explain the motions of the heavens in which the earth was the centre of the universe and all other celestial bodies revolved around it, espoused by Claudius Ptolemaeus in his work, the Almagest some time around the 2nd century, A.D., and accepted for over 1,000 years by the vast majority of Europeans to be the correct cosmological model. It may be also called the geocentric model. It was overthrown by the Copernican revolution after Galileo Galilei and Copernicus discovered that the planets orbited the sun.

The Almagest

An Epitome of the Almagest (Epitome in Ptolemaei Almagestum) was written between 1460 and 1463 by the Austrian astronomer Georg Peurbach and his famous pupil Johannes Regiomontanus at the suggestion of Cardinal Bessarion. It gave Europeans the first sophisticated understanding of Ptolemy's astronomy, and was studied by every competent astronomer of the 16th century. Unlike earlier systems (such as 'the stars move because that is the will of the gods', or the model of concentric spheres), the Ptolemaic model explained all phenomena in the sky, while holding to Plato's dictum which states that all motions in the heavens can be explained with uniform, circular motion, and obeying Aristotelian physics.

Geocentricity

According to the Ptolemaic model, the spherical Earth is at the center of the universe. All heavenly bodies are attached to crystal spheres which rotate around Earth. The Moon is on the innermost sphere, and touches the realm of Earth, thereby contaminating it, and causing the light and dark spots and the ability to go through phases. It is not perfect like the other heavenly bodies, which shine by their own light. The planets are actually attached to 2 spheres: one sphere which is centered on Earth (the deferent), and another sphere (the epicycle) embedded within the deferent. The epicycle rotates within the deferent, causing the planet to move closer to and farther from Earth at different points in its orbit, and even to slow down, stop, and move backward (in retrograde motion). (The earlier model based on concentric spheres explained retrograde motion, but did not explain the changes in brightness caused by the change in distance). The epicycles of Venus and Mercury are always centered on a line between Earth and the Sun (Mercury being closer to Earth), which explains why they are always near it in the sky. The order of spheres from Earth outward is: Earth, Moon, Mercury, Venus, Sun, Mars, Jupiter, Saturn, Stars.

Problems with geocentricity

Unfortunately, the system still did not quite match observations. Sometimes the size of a planet's retrograde loop (most notably that of Mars) would be smaller, and sometimes larger. Ptolemy could not explain this even when he moved deferents off-center, for the change in loop size did not match with the change in speed. This prompted Ptolemy to come up with the idea of an equant. The equant was a point near the center of a planet's orbit which, if you were to stand there and watch, the center of the planet's epicycle would always appear to move at the same speed. Therefore, the planet actually moved at different speeds at different points in its orbit. By using an equant, Ptolemy claimed to keep motion which was uniform and circular, but a lot of people didn't like it because they didn't think it was true to Plato's dictum of "uniform, circular motion." The resultant system which eventually became Catholic dogma was an unwieldy one, using two sets of epicycles, revolving on a deferent, offset by an equant which was different for each retrograde planet (then known to be only Mars, Jupiter, and Saturn), but it predicted the beginnings and ends of retrograde motion far more accurately than either earlier Platonic spheres or early (and falsely perfect) Copernican systems.

Replacement with Copernican system

Though there were observations made (primarily by Galileo) which called into question some of the tenets of the Ptolemaic system (such as the fact that Jupiter also has moons), it was not until the discovery of the phases of Venus by Galileo in 1610 that the Ptolemaic system became untenable in any form. Under the Ptolemaic system, Venus can only be either between Earth and the Sun, or on the other side of the Sun (Ptolemy placed it inside the orbit of the Sun, after Mercury, but this was completely arbitrary; he could just as easily swapped Venus and Mercury and put them on the other side, or any combination of placements of Venus and Mercury, as long as they were always colinear with Earth and Sun). If that was the case, however, it would not appear to go through all phases, as was observed. If it was between Earth and Sun, it would always appear mostly dark, since the light from the sun would be falling mainly where we can't see it. On the other hand, if it was on the far side, we would only be able to see the lit side. Galileo saw it small and full, and later large and crescent. Astronomers of this time period saw the result of this being unsalvageable for a Ptolemaic cosmology, if the results were accepted as true. As a result, later 17th century competition between astronomical cosmologies focused on variations of Tycho Brahe's Tychonian system (in which the Earth was still at the center of the universe, and around it revolved the Sun, but all other planets revolved around the Sun in one massive set of epicycles), or variations on the Copernican system.

References

Category:History of astronomy Category:Obsolete scientific theories Category:Systems

Claudius Ptolemaeus

:This article is about the geographer and astronomer Ptolemy. For Alexander the Great's general, see Ptolemy I Soter. For others named "Ptolemy" or "Ptolemaeus", see Ptolemy (disambiguation). Ptolemy (disambiguation).]] Claudius Ptolemaeus (Greek: Κλαύδιος Πτολεμαῖος; ca. 100 – ca. 178), known in English as Ptolemy, was an ancient geographer, astronomer, and astrologer who probably lived and worked in Alexandria, off the coast of Egypt. Ptolemy was the author of several scientific treatises, two of which have been of continuing importance to later Islamic and European science. One is the astronomical treatise that is now known as the Almagest (in Greek Η μεγάλη Σύνταξις, "The Great Treatise"). (See Ptolemaic system.) The other is the Geography, which is a thorough discussion of the geographic knowledge of the Greco-Roman world.

Astronomy

In the Almagest, one of the most influential books of classical antiquity, Ptolemy compiled the astronomical knowledge of the ancient Greek and Babylonian world; he relied mainly on the work of Hipparchus of three centuries earlier. It was preserved, like most of Classical Greek science, in Arabic manuscripts (hence its familiar name) and only made available in Latin translation (by Gerard of Cremona) in the 12th century. Ptolemy formulated a geocentric model that was widely accepted until it was superseded by the heliocentric solar system of Copernicus. Likewise his computational methods (supplemented in the 12th century with the Arabic computational Tables of Toledo) were of sufficient accuracy to satisfy the needs of astronomers, astrologers and navigators, until the time of the great explorations. They were also adopted in the Arab world and in India. The Almagest also contains a star catalogue, which is probably an updated version of a catalogue created by Hipparchus. Its list of forty-eight constellations is ancestral to the modern system of constellations, but unlike the modern system they did not cover the whole sky (only the sky Ptolemy could see).

Geographia

Ptolemy's other main work is his Geographia. This too is a compilation of what was known about the world's geography in the Roman Empire during his time. He relied mainly on the work of an earlier geographer, Marinos of Tyre, and on gazetteers of the Roman and ancient Persian empire, but most of his sources beyond the perimeter of the Empire were unreliable. The first part of the Geographia is a discussion of the data and of the methods he used. Like with the model of the solar system in the Almagest, Ptolemy put all this information into a grand scheme. He assigned coordinates to all the places and geographic features he knew, in a grid that spanned the globe. Latitude was measured from the equator, as it is today, but Ptolemy preferred to express it as the length of the longest day rather than degrees of arc (the length of the midsummer day increases from 12h to 24h as you go from the equator to the polar circle). He put the meridian of 0 longitude at the most western land he knew, the Canary Islands. Canary Islands), indicating the countries of "Serica" and "Sinae" (China) at the extreme right, beyond the island of "Taprobane" (Sri Lanka, oversized) and the "Aurea Chersonesus" (Southeast Asian peninsula).]] Ptolemy also devised and provided instructions on how to create maps both of the whole inhabited world (oikoumenè) and of the Roman provinces. In the second part of the Geographia he provided the necessary topographic lists, and captions for the maps. His oikoumenè spanned 180 degrees of longitude from the Canary islands in the Atlantic Ocean to China, and about 80 degrees of latitude from the Arctic to the East Indies and deep into Africa; Ptolemy was well aware that he knew about only a quarter of the globe. The maps in surviving manuscripts of Ptolemy's Geographia however, date only from about 1300, after the text was rediscovered by Maximus Planudes. Maps based on scientific principles had been made since the time of Eratosthenes (3rd century BC), but Ptolemy improved projections. It is known that a world map based on the Geographia was on display in Autun, France in late Roman times. In the 15th century Ptolemy's Geographia began to be printed with engraved maps; an edition printed at Ulm in 1482 was the first one printed north of the Alps. The maps look distorted as compared to modern maps, because Ptolemy's data were inaccurate. One reason is that Ptolemy estimated the size of the Earth as too small: while Eratosthenes found 700 stadia for a degree on the globe, in the Geographia Ptolemy uses 500 stadia. It is not certain if these geographers used the same stadion, but if we assume that they both stuck to the traditional Attic stadion of about 185 meters, then the older estimate is 1/6 too large, and Ptolemy's value is 1/6 too small. Because Ptolemy derived most of his topographic coordinates by converting measured distances to angles, his maps get distorted. So his values for the latitude were in error by up to 2 degrees. For longitude this was even worse, because there was no reliable method to determine geographic longitude; Ptolemy was well aware of this. It remained a problem in geography until the invention of chronometers at the end of the 18th century. It must be added that his original topographic list cannot be reconstructed: the long tables with numbers were transmitted to posterity through copies containing many scribal errors, and people have always been adding or improving the topographic data: this is a testimony to the persistent popularity of this influential work. In his Optics, a work which survives only in a poor Arabic translation, he writes about properties of light, including reflection, refraction and colour. His other works include Planetary Hypothesis, Planisphaerium and Analemma.

Ptolemy and astrology

Ptolemy's treatise on astrology, the Tetrabiblos, was the most popular astrological work of antiquity and also enjoyed great influence in the Islamic world and the medieval Latin West. The Tetrabiblos is an extensive and continually reprinted treatise on the ancient priciples of astrology in four books (Greek tetra means "four", biblos is "book"). That it did not quite attain the unrivalled status of the Syntaxis was perhaps because it did not cover some popular areas of the subject, particularly horary astrology (interpreting astrological charts for a particular moment to determine the outcome of a course of action to be initiated at that time), electional astrology, and medical astrology. The great popularity that the Tetrabiblos did possess might be attributed to its nature as an exposition of the art of astrology and as a compendium of astrological lore, rather than as a manual. It speaks in general terms, avoiding illustrations and details of practice. Ptolemy was concerned to defend astrology by defining its limits, compiling astrological data that he believed was reliable and dismissing practices (such as considering the numerological significance of names) that he believed to be without sound basis. Much of the content of the Tetrabiblos may well have been collected from earlier sources; Ptolemy's achievement was to order his material in a systematic way, showing how the subject could, in his view, be rationalized. It is, indeed, presented as the second part of the study of astronomy of which the Syntaxis was the first, concerned with the influences of the celestial bodies in the sublunar sphere. Thus explanations of a sort are provided for the astrological effects of the planets, based upon their combined effects of heating, cooling, moistening, and drying. Ptolemy's astrological outlook was quite practical: he thought that astrology was like medicine, that is conjectural, because of the many variable factors to be taken into account: the race, country, and upbringing of an person affects an individual's personality as much if not more than the positions of the Sun, Moon, and planets at the precise moment of their birth, so Ptolemy saw astrology as something to be used in life but in no way relied on entirely.

Ptolemy and music

Ptolemy also wrote an influential work, Harmonics on music theory. After criticizing the approaches of his predecessors, Ptolemy argued for basing musical intervals on mathematical ratios (in contrast to the followers of Aristoxenus) backed up by empirical observation (in contrast to the overly-theoretical approach of the Pythagoreans). He presented his own divisions of the tetrachord and the octave, which he derived with the help of a monochord. Ptolemy's astronomical interests also appeared in a discussion of the music of the spheres.

Named after Ptolemy

- Ptolemaeus crater on the Moon.
- Ptolemaeus crater on Mars.

References

- Berggren, J. Lennart and Jones, Alexander. 2000. Ptolemy's Geography: An Annotated Translation of the Theoretical Chapters. Princeton University Press. Princeton and Oxford. ISBN 0-691-01042-0.
- Stevenson, Edward Luther. Trans. and ed. 1932. Claudius Ptolemy: The Geography. New York Public Library. Reprint: Dover, 1991. (This is the only complete English translation of Ptolemy's most famous work. Unfortunately, it is marred by numerous mistakes and the placenames are given in Latinised forms, rather than in the original Greek).

External links

Primary sources

- [http://penelope.uchicago.edu/Thayer/E/Roman/Texts/Ptolemy/Tetrabiblos/home.html Ptolemy's Tetrabiblos at LacusCurtius] (English translation, with introductory material)
- [http://penelope.uchicago.edu/Thayer/E/Gazetteer/Periods/Roman/_Texts/Ptolemy/home.html Ptolemy's Geography at LacusCurtius] (English translation, incomplete)
- [http://dsr.nii.ac.jp/toyobunko/III-2-F-b-2/V-1/page/0162.html.ja Extracts of Ptolemy on the country of the Seres (China)] (English translation)

Secondary material

- [http://www.skyscript.co.uk/ptolemy.html Ptolemy at SkyScript] - The Life and Work of Ptolemy
- [http://www.chass.utoronto.ca/~ajones/ptolgeog/ Alexander Jones, "Ptolemy and his Geography"]
- [http://obs.nineplanets.org/psc/theman.html Ptolemy biography] (Bill Arnett's site)
- [http://wwwuser.gwdg.de/~fhasele/ptolemaeus/index.html Ptolemy's Geography of Asia] - Selected problems of Ptolemy's Geography of Asia (currently in German)
- [http://www.fiks.de/rom/index.htm?rom10.htm Ptolemy's Geography of Northwestern Europe]
- [http://www.newberry.org/smith/slidesets/ss08.html History of Cartography] including a discussion of the Geographica
- [http://www.csiss.org/classics/content/76 Claudius Ptolemaeus (Ptolemy): Representation, Understanding, and Mathematical Labeling of the Spherical Earth] Ptolemy Ptolemy Ptolemy Ptolemy Ptolemy
- Ptolemy Ptolemy ko:클라우디오스 프톨레마이오스 ja:クラウディオス・プトレマイオス th:ทอเลมี

Almagest

Almagest is the Latin form of the Arabic name (al-kitabu-l-mijisti, i.e. "The Great Book") of an astronomical/astrological treatise proposing the complex motions of the stars and planetary paths, originally written in Greek as Hè Megalè Syntaxis by Ptolemy of Alexandria, Egypt. The date of Almagest has recently been more precisely established. Ptolemy set up a public inscription at Canopus in Egypt in 147/148 C.E. The late N. T. Hamilton found that the version of Ptolemy's models set out in the Canopic Inscription was earlier than the version in Almagest. Hence Almagest cannot have been completed before about C.E. 150, a quarter century after Ptolemy began observing [http://www.chass.utoronto.ca/~ajones/ptolgeog/biography.html]. Its geocentric model was accepted as correct for over a thousand years in Arab and European societies. The first translations into Arabic were made in the 9th century, with two separate efforts, one sponsored by the caliph Al-Ma'mun. By this time, the work was lost in Europe, or only dimly remembered in astrological lore. Consequently, Western Europe rediscovered Ptolemy from translations of Arabic versions. In the twelfth century a Spanish version was produced, later turned into Latin under the patronage of Emperor Frederick II. Another Latin version, this time directly from the Arabic, was produced by Gerard of Cremona, who found his text in Toledo in Spain. Gerard of Cremona was unable to translate many technical terms, even retained the Arabic Abrachir for Hipparchus. In the 15th century, a Greek version appeared in Western Europe, and Johannes Müller, better known as Regiomontanus, made an abridged Latin version at the instigation of the brilliant Greek churchman Johannes, Cardinal Bessarion. At the same time, a full translation was made by George of Trebizond. It included a commentary that was as long as the original. The work of translation, done under the patronage of Pope Nicholas V was intended to supplant the old translation. The new manuscripts were a great improvement; the new commentary was not, and aroused much heated criticism. The Pope declined the dedication of the translation, and Regiomontanus' translation had the upper hand for the next century and more.
- Commentaries on Almagest were written by Theon of Alexandria (extant), Pappus (fragments), and Ammonius (lost).

External links

- [http://astro.isi.edu/reference/almagest.html Online copy of the star catalog in the Almagest]
- [http://www.phys.uu.nl/~vgent/astro/ancientephemerides.htm Online luni-solar & planetary ephemeris calculator based on the Almagest] Category:Roman era books Category:Arabic words category:astronomy books

Galileo Galilei

Galileo Galilei (Pisa, February 15 1564 – Arcetri, January 8 1642), was an Italian physicist, astronomer, and philosopher who is closely associated with the scientific revolution. His achievements include improvements to the telescope, a variety of astronomical observations, the first law of motion and the second law of motion, and effective support for Copernicanism. He has been referred to as the "father of modern astronomy," as the "father of modern physics," and as "father of science." His experimental work is widely considered complementary to the writings of Francis Bacon in establishing the modern scientific method. Galileo's career coincided with that of Johannes Kepler. The work of Galileo is considered to be a significant break from that of Aristotle. In addition, his conflict with the Roman Catholic Church is taken as a major early example of the conflict of authority and freedom of thought, particularly with science, in Western society.

Galileo's Family & Early Careers

Galileo was born in Pisa, in the Tuscan region of Italy, the son of Vincenzo Galilei, a mathematician and musician born in Florence in 1520, and Giulia Ammannati, born in Pescia and married in 1563. Galileo was their first child. Although a devout Catholic, Galileo fathered three children out of wedlock. All were the children of Galileo and Marina Gamba. Because of their illegitimate birth, both girls were sent to the convent of San Matteo in Arcetri at early ages.
- Virginia (b. 1600) who took the name Maria Celeste upon entering a convent. Galileo's eldest child, the most beloved, and inherited her father's sharp mind. She died in 1634 on April second. She is buried with Galileo at the Basilica di Santa Croce di Firenze.
- Livia (b. 1601) took the name Suor Arcangela. Was sickly for most of her life at the convent.
- Vincenzio (b. 1606) was later legitimized and married Sestilia Bocchineri He was home schooled at a very young age. After that he attended the University of Pisa, but was forced to cease his study there for financial reasons. However, he was offered a position on its faculty in 1589 and taught mathematics. Soon after, he moved to the University of Padua, and served on its faculty teaching geometry, mechanics, and astronomy until 1610. During this time he explored science and made many landmark discoveries.

Experimental science

In the pantheon of the scientific revolution, Galileo takes a high position because of his pioneering use of quantitative experiments with results analyzed mathematically. There was no tradition of such methods in European thought at that time; the great experimentalist who immediately preceded Galileo, William Gilbert, did not use a quantitative approach. However, Galileo's father, Vincenzo Galilei, had performed experiments in which he discovered what may be the oldest known non-linear relation in physics, between the tension and the pitch of a stretched string. Galileo also contributed to the rejection of blind allegiance to authority (like the Church) or other thinkers (such as Aristotle) in matters of science and to the separation of science from philosophy or religion. These are the primary justifications for his description as the "father of science." In the 20th century some authorities challenged the reality of Galileo's experiments, in particular the distinguished French historian of science Alexandre Koyré. The experiments reported in Two New Sciences to determine the law of acceleration of falling bodies, for instance, required accurate measurements of time, which appeared to be impossible with the technology of the 1600s. According to Koyré, the law was arrived at deductively, and the experiments were merely illustrative thought experiments. Later research, however, has validated the experiments. The experiments on falling bodies (actually rolling balls) were replicated using the methods described by Galileo (Settle, 1961), and the precision of the results was consistent with Galileo's report. Later research into Galileo's unpublished working papers from as early as 1604 clearly showed the reality of the experiments and even indicated the particular results that led to the time-squared law (Drake, 1973).

Astronomy

Contributions

Although the popular idea of Galileo inventing the telescope is inaccurate, he was one of the first people to use the telescope to observe the sky, and for a time was one of very few people able to make a good enough telescope for the purpose. Based on sketchy descriptions of telescopes invented in the Netherlands in 1608, Galileo made one with about 8x magnification, and then made improved models up to about 20x. On August 25, 1609, he demonstrated his first telescope to Venetian lawmakers. His work on the device also made for a profitable sideline with merchants who found it useful for their shipping businesses. He published his initial telescopic astronomical observations in March 1610 in a short treatise entitled Sidereus Nuncius (Sidereal Messenger). Sidereus Nuncius. This observation upset the notion that all celestial bodies must revolve around the Earth. Galileo published a full description in Sidereus Nuncius in March 1610.]] On January 7, 1610 Galileo discovered three of Jupiter's four largest satellites (moons): Io, Europa, and Callisto. Ganymede he discovered four nights later. He determined that these moons were orbiting the planet since they would appear and disappear; something he attributed to their movement behind Jupiter. He made additional observations of them in 1620. Later astronomers overruled Galileo's naming of these objects, changing his Medicean stars to Galilean satellites. The demonstration that a planet had smaller planets orbiting it was problematic for the orderly, comprehensive picture of the geocentric model of the universe, in which everything circled around the Earth. Galileo noted that Venus exhibited a full set of phases like the Moon. The heliocentric model of the solar system developed by Copernicus predicted that all phases would be visible since the orbit of Venus around the Sun would cause its illuminated hemisphere to face the Earth when it was on the opposite side of the Sun and to face away from the Earth when it was on the Earth-side of the Sun. By contrast, the geocentric model of Ptolemy predicted that only crescent and new phases would be seen, since Venus was thought to remain between the Sun and Earth during its orbit around the Earth. Galileo's observation of the phases of Venus proved that Venus orbited the Sun and lent support to (but did not prove) the heliocentric model. Galileo was one of the first Europeans to observe sunspots, although there is evidence that Chinese astronomers had done so before. The very existence of sunspots showed another difficulty with the unchanging perfection of the heavens as assumed in the older philosophy. And the annual variations in their motions, first noticed by Francesco Sizzi, presented great difficulties for either the geocentric system or that of Tycho Brahe. A dispute over priority in the discovery of sunspots led to a long and bitter feud with Christoph Scheiner; in fact, there can be little doubt that both of them were beaten by David Fabricius and his son Johannes. He was the first to report lunar mountains and craters, whose existence he deduced from the patterns of light and shadow on the Moon's surface. He even estimated the mountains' heights from these observations. This led him to the conclusion that the Moon was "rough and uneven, and just like the surface of the Earth itself", and not a perfect sphere as Aristotle had claimed. Galileo observed the Milky Way, previously believed to be nebulous, and found it to be a multitude of stars, packed so densely that they appeared to be clouds from Earth. He also located many other stars too distant to be visible with the naked eye. Galileo observed the planet Neptune in 1612, but did not realize that it was a planet and took no particular notice of it. It appears in his notebooks as one of many unremarkable dim stars.

Modern claims of scientific errors and misconduct

Although Galileo is generally considered one of the first modern scientists, as evidenced by his position in the sunspot controversy, he is often said to have arrogantly considered himself to be the sole-propietor of the discoveries in astronomy. Furthermore, he never accepted Kepler's elliptical orbits for the planets, holding to the circular orbits of Copernicus, which still employed epicycles to account for irregularities in planetary motions. Concerning his theory on tides, Galileo attributed them to momentum despite his great knowledge of the ideas of relative motion and Kepler's better theories using the Moon as the cause. (Neither of these great scientists, however, had a workable physical theory of tides; this had to wait for the work of Newton) Galileo stated in his Dialogue that, if the Earth spins on its axis and is traveling at a certain speed around the Sun, parts of the Earth must travel "faster" at night and "slower" during the day. This, of course, is true in the Sun's frame of reference; but it is by no means adequate to explain the tides. Many commentators consider that Galileo developed this position simply to justify his own opinion because the theory was not based on any real scientific observations because if his theory was correct, there would be only one high tide per day and it would happen at noon. The fact that there are two daily high tides at Venice instead of one, and that they travel around the clock, Galileo and his contemporaries knew, but he dismissed as due to several secondary causes, such as the shape of the sea, its depth, and other things. Against the imputation that Galileo was guilty of some kind of deceit in making these arguments one may take the position of Albert Einstein, as one who had done original work in physics, that Galileo developed his "fascinating arguments" and accepted them too uncritically out of a desire for a physical proof of the motion of the Earth (Einstein, 1952)

Physics

Galileo's theoretical and experimental work on the motions of bodies, along with the largely independent work of Kepler and René Descartes, was a precursor of the Classical mechanics developed by Sir Isaac Newton. He was a pioneer, at least in the European tradition, in performing rigorous experiments and insisting on a mathematical description of the laws of nature. One of the most famous stories about Galileo is that he dropped balls of different masses from the Leaning Tower of Pisa to demonstrate that their time of descent was independent of their mass (excluding the limited effect of air resistance). This was contrary to what Aristotle had taught: that heavy objects fall faster than lighter ones, in direct proportion to weight. Though the story of the tower first appeared in a biography by Galileo's pupil Vincenzo Viviani, it is not now generally accepted as true. However, Galileo did perform experiments involving rolling balls down inclined planes, which proved the same thing: falling or rolling objects (rolling is a slower version of falling, as long as the distribution of mass in the objects is the same) are accelerated independently of their mass. He determined the correct mathematical law for acceleration: the total distance covered, starting from rest, is proportional to the square of the time (This law is regarded as a predecessor to the many later scientific laws expressed in mathematical form.). He also concluded that objects retain their velocity unless a force -- often friction -- acts upon them, refuting the accepted Aristotelian hypothesis that objects "naturally" slow down and stop unless a force acts upon them. Galileo's Principle of Inertia stated: "A body moving on a level surface will continue in the same direction at constant speed unless disturbed." This principle was incorporated into Newton's laws of motion (1st law). Newton's laws of motion Galileo also noted that a pendulum's swings always take the same amount of time, independently of the amplitude. The story goes that he came to this conclusion by watching the swings of the bronze chandelier in the cathedral of Pisa, using his pulse to time it. While Galileo believed this equality of period to be exact, it is only an approximation appropriate to small amplitudes. It is good enough to regulate a clock, however, as Galileo may have been the first to realize. (See Technology below) In the early 1600s, Galileo and an assistant tried to measure the speed of light. They stood on different hilltops, each holding a shuttered lantern. Galileo would open his shutter, and, as soon as his assistant saw the flash, he would open his shutter. At a distance of less than a mile, Galileo could detect no delay in the round-trip time greater than when he and the assistant were only a few yards apart. While he could reach no conclusion on whether light propagated instantaneously, he recognized that the distance between the hilltops was perhaps too small for a good measurement. Galileo is lesser known for, yet still credited with being one of the first to understand sound frequency. After scraping a chisel at different speeds, he linked the pitch of sound to the spacing of the chisel's skips (frequency). In his 1632 Dialogue Galileo presented a physical theory to account for tides, based on the motion of the Earth. If correct, this would have been a strong argument for the reality of the Earth's motion. (The original title for the book, in fact, described it as a dialogue on the tides; the reference to tides was removed by order of the Inquisition.) His theory gave the first insight into the importance of the shapes of ocean basins in the size and timing of tides; he correctly accounted, for instance, for the negligible tides halfway along the Adriatic Sea compared to those at the ends. As a general account of the cause of tides, however, his theory was a failure. Kepler and others correctly associated the Moon with an influence over the tides, based on empirical data; a proper physical theory of the tides, however, was not available until Newton. Galileo also put forward the basic principle of relativity, that the laws of physics are the same in any system that is moving at a constant speed in a straight line, regardless of its particular speed or direction. Hence, there is no absolute motion or absolute rest. This principle provided the basic framework for Newton's laws of motion and Einstein's theory of relativity.

Mathematics

While Galileo's application of mathematics to experimental physics was innovative, his mathematical methods were the standard ones of the day. The analyses and proofs relied heavily on the Eudoxian theory of proportion, as set forth in the fifth book of Euclid's Elements. This theory had become available only a century before, thanks to accurate translations by Tartaglia and others; but by the end of Galileo's life it was being superseded by the algebraic methods of Descartes, which a modern finds incomparably easier to follow. Galileo produced one piece of original and even prophetic work in mathematics: Galileo's paradox, which shows that there are as many perfect squares as there are whole numbers, even though most numbers are not perfect squares. Such seeming contradictions were brought under control 250 years later in the work of Georg Cantor.

Technology

Galileo made a few contributions to what we now call technology as distinct from pure physics, and suggested others. This is not the same distinction as made by Aristotle, who would have considered all Galileo's physics as techne or useful knowledge, as opposed to episteme, or philosophical investigation into the causes of things. In 1595–1598, Galileo devised and improved a "Geometric and Military Compass" suitable for use by gunners and surveyors. This expanded on earlier instruments designed by Niccolo Tartaglia and Guidobaldo del Monte. For gunners, it offered, in addition to a new and safer way of elevating cannons accurately, a way of quickly computing the charge of gunpowder for cannonballs of different sizes and materials. As a geometric instrument, it enabled the construction of any regular polygon, computation of the area of any polygon or circular sector, and a variety of other calculations. About 1606–1607 (or possibly earlier), Galileo made a thermometer, using the expansion and contraction of air in a bulb to move water in an attached tube. In 1609, Galileo was among the first to use a refracting telescope as an instrument to observe stars, planets or moons. In 1610, he used a telescope as a compound microscope, and he made improved microscopes in 1623 and after. This appears to be the first clearly documented use of the compound microscope. In 1612, having determined the orbital periods of Jupiter's satellites, Galileo proposed that with sufficiently accurate knowledge of their orbits one could use their positions as a universal clock, and this would make possible the determination of longitude. He worked on this problem from time to time during the remainder of his life; but the practical problems were severe. The method was first successfully applied by Giovanni Domenico Cassini in 1681 and was later used extensively for land surveys; for navigation, the first practical method was the chronometer of John Harrison. In his last year, when totally blind, he designed an escapement mechanism for a pendulum clock. The first fully operational pendulum clock was made by Christiaan Huygens in the 1650s. He created sketches of various inventions, such as a candle and mirror combination to reflect light throughout a building, an automatic tomato picker, a pocket comb that doubled as an eating utensil, and what appears to be a ballpoint pen. ballpoint pen

Church controversy

:Main article: Trial of Galileo. Not long after Galileo began publishing his astronomical work in The Starry Messenger, his Copernican ideas came under attack as a possible heresy, violating the Biblical picture of the Earth as the center of the universe (as well as the accepted philosophical teachings of the time). By 1616 the attacks seemed to Galileo to have become dangerous, and he went to Rome to try to persuade the Church authorities not to ban the new teachings. The mission was a failure: in the end, Cardinal Bellarmine, acting on orders from the Pope, delivered him an order not hold or defend the idea that the Earth moves and the Sun stands still at the center. For the next several years Galileo stayed well away from the controversy. Toward 1630, however, he revived his project of writing a book on the subject, encouraged by the election of Pope Urban VIII. The book, Dialogue Concerning the Two Chief World Systems, was published in 1632, with formal authorization from the Inquisition; there is dispute, however, concerning this license. Galileo was ordered to Rome to stand trial on suspicion of heresy in 1633. The sentence of the Inquisition was in three essential parts:
- Galileo was required to recant his heliocentric ideas, which were condemned as "formally heretical";.
- He was ordered imprisoned; the sentence was later commuted to house arrest.
- His offending Dialogue was banned; and in an action not announced at the trial, publication of any of his works was forbidden, including any he might write in the future. After a period with the friendly Archbishop Piccolomini in Siena, Galileo was allowed to return to his villa at Arcetri near Florence, where he spent the remainder of his life under house arrest.

Galileo's writings

Arcetri
- Two New Sciences 1638 Lowys Elzevir (Louis Elsevier) Leiden (in Italian, Discorsi e Dimostrazioni Matematiche, intorno á due nuoue scienze Leida, Appresso gli Elsevirii 1638)
- Dialogue Concerning the Two Chief World Systems 1632 (in Italian, Dialogo dei due massimi sistemi del mondo)
- The Starry Messenger 1610 Venice (in Latin, Sidereus Nuncius)
- Letter to Grand Duchess Christina

Writings on Galileo

- Galileo Galilei, an opera by Philip Glass
- Galileo a play by Bertolt Brecht

References

- Drake, Stillman (1953). Dialogue Concerning the Two Chief World Systems. Berkeley: University of California Press.
- Drake, Stillman (1957). Discoveries and Opinions of Galileo. New York: Doubleday & Company. ISBN 0-385-09239-3
- Drake, Stillman (1973). "Galileo's Discovery of the Law of Free Fall". Scientific American v. 228, #5, pp. 84-92.
- Drake, Stillman (1978). Galileo At Work. Chicago: University of Chicago Press. ISBN 0-226-16226-5
- Einstein, Albert (1952). Foreword to (Drake, 1953)
- Fantoli, Annibale (2003). Galileo — For Copernicanism and the Church, third English edition. Vatican Observatory Publications. ISBN 88-209-7427-4
- Fillmore, Charles (1931, 17th printing July 2004). Metaphysical Bible Dictionary. Unity Village, Missouri: Unity House. ISBN 0-871-59067-0
- Hellman, Hal (1988). Great Feuds in Science. Ten of the Liveliest Disputes Ever. New York: Wiley.
- Lessl, Thomas, "[http://www.catholiceducation.org/articles/apologetics/ap0138.html The Galileo Legend]". New Oxford Review, 27-33 (June 2000).
- Newall, Paula (2004). [http://www.galilean-library.org/hps.html "The Galileo Affair."]
- Settle, Thomas B. (1961). "An Experiment in the History of Science". Science, 133:19-23.
- Sobel, Dava. (1999). Galileo's Daughter. ISBN: 0-140-28055-3
- White, Andrew Dickson (1898). [http://www.santafe.edu/~shalizi/White/ A History of the Warfare of Science with Theology in Christendom]. New York 1898.

Named after Galileo

- The Galileo mission to Jupiter
- The Galilean moons of Jupiter
- Galileo Regio on Ganymede
- Galilaei crater on the Moon
- Galilaei crater on Mars
- Asteroid 697 Galilea (named on the occasion of the 300th anniversary of the discovery of the Galilean moons)
- Galileo (unit of acceleration)
- Galileo positioning system
- Galileo stadium in Miami, Florida

Notes

- Note 1: [http://www.lucidcafe.com/library/96feb/galileo.html Galileo, Lucid Cafe Feb '96]"

External links

- [http://www.newadvent.org/cathen/06342b.htm Galileo Galilei article at the Old Catholic Encyclopedia]
- [http://www.galilean-library.org/hps.html The Galileo Affair] by Paula Newall.
- [http://www.infidels.org/library/historical/andrew_white/Chapter3.html The Warfare of Science With Theology]
- [http://galileo.rice.edu/ The Galileo Project] at Rice University
- [http://www.pacifier.com/~tpope CCD Images through a Galilean Telescope] Modern recreation of what Galileo might have seen
- [http://wspace.danask.com/g/galileo_galilei.html about Galileo Galilei] at danask.com
- [http://www.mpiwg-berlin.mpg.de/Galileo_Prototype/MAIN.HTM Electronic representation of Galilei's notes on motion (MS. 72)]
- [http://www.firstthings.com/ftissues/ft0401/reviews/barr.html From Myth to History and Back] — Reviews of two books on Galileo
- [http://www.pbs.org/wgbh/nova/galileo/ PBS Nova Online: Galileo's Battle for the Heavens]
- [http://plato.stanford.edu/entries/galileo/ Stanford Encyclopedia of Philosophy entry]
- [http://www.galilean-library.org The Galilean Library], an educational site dedicated to Galileo
- [http://www.liberliber.it/biblioteca/g/galilei/ Galileo's writings in italian language], an italian site dedicated to free e-texts
- [http://www.newadvent.org/cathen/06342b.htm Galielo Galilei, in the Catholic Encyclopedia] found online on New Advent, an orthodox Catholic website Galilei Galilei Category:Astrologers Galilei Galilei Galilei Galilei Galilei als:Galileo Galilei ko:갈릴레오 갈릴레이 ja:ガリレオ・ガリレイ simple:Galileo Galilei th:กาลิเลโอ กาลิเลอี

1460

Events

- The first Portuguese navigators reach the coast of modern Sierra Leone.
- March 5 - King Christian I of Denmark declares the unity of the two provinces of Schleswig and Holstein, who have been treated as one ever since (albeit under different national affiliations).
- March 6 - Treaty of Alcacovas - Portugal gives Castile the Canary Islands in exchange for claims in West Africa
- June - The Earl of Warwick and Edward, Earl of March, eldest son of the Duke of York, land in England with an army and seize London.
- July 18 - Battle of Northampton - Warwick and March defeat a Lancastrian army and seize King Henry. It is agreed that York will be Henry's heir, disinheriting the King's son Edward of Westminster, Prince of Wales.
- December 30 - Battle of Wakefield - A Lancastrian army under Henry Beaufort, Duke of Somerset and Henry Percy, Earl of Northumberland defeats a Yorkist army under the Duke of York and his son, Edmund, Earl of Rutland. Both York and Rutland are killed, the latter murdered after the battle. York's son Edward becomes leader of the Yorkist faction.

Births

- May 8 - Frederick I, Margrave of Brandenburg-Ansbach (died 1536)
- Judah Leon Abravanel, Jewish philosopher, physician, and poet
- Antoine Brumel, Flemish composer (died 1515)
- Elijah Delmedigo, Italian philosopher (died 1497)
- Edward Sutton, 2nd Baron Dudley (died 1532)
- Juan Pérez de Gijón, Spanish composer (died 1500)
- Konstanty Ostrogski, Grand Hetman of Lithuania (died 1530)
- Vicente Yáñez Pinzón, Spanish navigator (died 1523)
- Tilman Riemenschneider, German sculptor (died 1531)
- Arnolt Schlick, German organist and composer
- Charles Somerset, 1st Earl of Worcester (died 1526)
- Tristão da Cunha, Portuguese explorer (died 1540)

Deaths

- July 10 - Humphrey Stafford, 1st Duke of Buckingham, English military leader (born 1402)
- August 3 - King James II of Scotland (born 1430)
- September 20 - Gilles Binchois, Flemish composer
- November 13 - Prince Henry the Navigator, Portuguese patron of exploration (born 1394)
- December 14 - Guarino da Verona, Italian humanist (born 1370)
- December 30 - Richard Plantagenet, 3rd Duke of York, claimant to the English throne (killed in battle) (born 1411)
- December 31 - Richard Neville, 5th Earl of Salisbury, English politician (executed) (born 1400)
- December 31 - Edmund, Earl of Rutland, brother of Kings Edward IV of England and Richard III of England (executed) (b. 1443)
- Francesco II Acciajouli, last Duke of Athens
- Israel Isserlein, German Jewish scholar
- Reginald Pecock, English prelate and writer Category:1460 ko:1460년

Regiomontanus

Johannes Müller von Königsberg (June 6, 1436 – July 6, 1476), known by his Latin pseudonym Regiomontanus, was an important German mathematician, astronomer and astrologer. He was born in the Franconian village of Unfinden near Königsberg, Bavaria (not to be confused with the East Prussian city of Königsberg, now known as Kaliningrad). He is also called Johannes Müller, der Königsberger (Johannes Müller of Königsberg). His full Latin name was Joannes de Regio monte, which abbreviated to Regiomontanus (from the Latin for "Königsberg"—"King's Mountain"). At eleven years of age, he became a student at the university in Leipzig, Saxony. Three years later he continued his studies at Alma Mater Rudolfina, the university in Vienna, Austria. There he became a pupil and friend of Georg von Peurbach. In 1457 he graduated with a degree of "magister artium" (Master of Arts) and held lectures in optics and ancient literature. He built astrolabes for Matthias Corvinus of Hungary and Cardinal Bessarion, and in 1465 a portable sundial for Pope Paul II. His work with Peurbach brought him to the writings of Nicholas of Cusa (Cusanus), who held a heliocentric view. Regiomontanus, however, remained a geocentrist after Ptolemy. Following Peurbach's death, he continued the translation of Ptolemy's Almagest which Peurbach had begun at the initiative of Johannes Bessarion. From 1461 to 1465 Regiomontanus lived and worked at Cardinal Bessarion's house in Rome. He wrote De Triangulis omnimodus (1464) and Epytoma in almagesti Ptolemei. De Triangulis (On Triangles) was one of the first textbooks presenting the current state of trigonometry and included lists of questions for review of individual chapters. In it he wrote: :"You who wish to study great and wonderful things, who wonder about the movement of the stars, must read these theorems about triangles. Knowing these ideas will open the door to all of astronomy and to certain geometric problems." In the Epytoma he critiqued the translation, pointing out inaccuracies. Later Nicolaus Copernicus would refer to this book as an influence on his own work. In 1467 Regiomontanus left Rome to work at the court of Matthias Corvinus of Hungary. There he calculated extensive astronomical tables and built astronomical instruments. In 1471 he moved to the Free City of Nuremberg, in Franconia, then one of the Empire's important seats of learning, publication, commerce and art. Regiomontanus remains famous for having built at Nuremberg the first astronomical observatory in Germany, perhaps in Europe. There he published many astronomical charts. In 1475 he went to Rome to work with Pope Sixtus IV on calendar reform. While there, Regiomontanus died mysteriously: some say of plague, others by (more likely) assassination. That was on July 6, 1476, when he had just turned forty a month earlier. Domenico Maria Novara da Ferrara, the teacher of Nicolaus Copernicus, referred to Regiomontanus as having been his own teacher. A prolific author, Regiomontanus was internationally famous already in his lifetime. Despite having completed only a quarter of what he had intended to write, he left a substantial body of work. It is not true that he came to be called posthumously after the place of his birth, Königsberg (in Latin, Regiomontanus). In Regiomontanus' day it was common for scholars to Latinize their names when publishing. Copernicus did likewise, which is why we do not know him today by his actual name, Nikołai Kopernik.

Regiomontanus and Astrology

One biographer has claimed to have detected a decline in Regiomontanus' interest in astrology over his life, and came close to asserting that Regiomontanus had rejected it altogether. But more recent commentators have suggested that the occasional expression of skepticism about astrological prognostication reflected a disquiet about the procedural rigor of the art, not about its underlying principles. It seems plausible that, like some other astronomers, Regiomontanus concentrated his efforts on mathematical astronomy because he felt that astrology could not be placed on a sound footing until the celestial motions had been modeled accurately. In his youth, Regiomontanus had cast horoscopes (natal charts) for famous patrons. His Tabulae directionum, completed in Hungary, were designed for astrological use and contained a discussion of different ways of determining astrological houses. The calendars for 1475-1531 which he printed at Nuremberg contained only limited astrological information—a method of finding times for bloodletting according to the position of the moon; subsequent editors added material. But perhaps the works most indicative of Regiomontanus' hopes for an empirically sound astrology were his almanacs or ephemerides, produced first in Vienna for his own benefit, and printed in Nuremberg for the years 1475-1506. Weather predictions and observations were juxtaposed by Regiomontanus in his manuscript almanacs, and the form of the printed text enabled scholars to enter their own weather observations in order to likewise check astrological predictions; extant copies reveal that several did so. Regiomontanus' Ephemeris would be used in 1504, by a Christopher Columbus stranded on Jamaica, to intimidate the natives into continuing to provision him and his crew from their scanty food stocks, when he successfully predicted a lunar eclipse for February 29, 1504. Regiomontanus did not live to produce the special commentary to the ephemerides that he had promised would reveal the advantages the almanacs held for the multifarious activities of physicians, for human births and the telling of the future, for weather forecasting, for the inauguration of employment, and for a host of other activities, although this lack was again made good by subsequent editors. Nevertheless Regiomontanus' promise suggests that he either was as convinced of the validity and utility of astrology as his contemporaries, or was willing to set aside his misgivings for the sake of commercial success.

External links

- Adam Mosley, [http://www.hps.cam.ac.uk/starry/regiomontanus.html Regiomontanus Biography], web site at the Department of History and Philosophy of Science of the University of Cambridge (1999).
- Regiomontanus Regiomontanus Regiomontanus Regiomontanus Regiomontanus Regiomontanus Regiomontanus

16th century

As a means of recording the passage of time, the 16th century was that century which lasted from 1501 to 1600. See also: 16th century in literature

Events

- 1501: Safavid dynasty rules Iran until 1736.
- 1509: The Battle of Diu marks the beginning of Portuguese dominance of the Spice trade.
- 1514: The Battle of Orsha halts Muscovy's expansion into Eastern Europe.
- 1515: The Ottoman Empire wrests Eastern Anatolia from the Safavids after the Battle of Chaldiran.
- 1516-17: The Ottomans defeat the Mamluks and gain control of Egypt, Arabia, and the Levant.
- 1517: The Protestant Reformation begins when Martin Luther posts his 95 Theses in Saxony.
- 1519-21: Hernán Cortés leads the Spanish conquest of the Aztec Empire.
- 1520-66: The reign of Suleiman the Magnificent marks the zenith of the Ottoman Empire.
- 1521: Belgrade is captured by the Ottoman Empire.
- 1523: Sweden gains independence from the Kalmar Union.
- 1524-25: Peasants' War in the Holy Roman Empire.
- 1526: The Ottomans conquer the Kingdom of Hungary at the Battle of Mohács.
- 1526: Mughal Empire, founded by Babur, rules India until 1857.
- 1527: Sack of Rome is considered the end of the Italian Renaissance.
- 1529: The Siege of Vienna marks the Ottoman Empire's furthest advance into Europe.
- 1531-32: The Church of England breaks away from the Roman Catholic Church and recognizes King Henry VIII as the head of the Church.
- 1532: Francisco Pizarro leads the Spanish conquest of the Inca Empire.
- 1534: Jacques Cartier claims Quebec for France.
- 1534: The Ottomans capture Baghdad.
- 1543: The Nanban trade period begins after Portuguese traders make contact with Japan.
- 1552: Russia conquers the Khanate of Kazan.
- 1553: Macau founded by Portuguese in China.
- 1555: The Muscovy Company is the first major English joint stock trading company.
- 1556: The Shaanxi Earthquake in China is history's deadliest known earthquake.
- 1556: Russia conquers the Astrakhan Khanate.
- 1556-1605: During his reign, Akbar expands the Mughal Empire in a series of conquests and is considered the greatest Mughal emperor.
- 1558-1603: The Elizabethan era is considered the height of the English Renaissance.
- 1558-83: Livonian War between Poland, Sweden, Denmark and Russia.
- 1558: After 200 years, England loses Calais to France.
- 1559: With the Peace of Cateau Cambrésis, the Italian Wars conclude.
- 1562-98: French Wars of Religion between Catholics and Huguenots.
- 1566-1648: Eighty Years' War between Spain and the Netherlands.
- 1568-1600: The Azuchi-Momoyama period in Japan.
- 1569: The Polish-Lithuanian Commonwealth is created with the Union of Lublin which lasts until 1795.
- 1577-80: Francis Drake circles the World and claims California for England.
- 1580: After the struggle for the throne of Portugal, the Portuguese Empire comes to an end and the Spanish and Portuguese crowns are united for 60 years.
- 1582: Yermak Timofeyevich conquers the Siberia Khanate on behalf of the Stroganovs.
- 1584-85: After the Siege of Antwerp, many of its merchants fled to Amsterdam.
- 1585-1604: The Anglo-Spanish War is fought on both sides of the Atlantic.
- 1588: England repulses the Spanish Armada.
- 1589: Spain repulses the English Armada.
- 1592-98: Korea and China repel two Japanese invasions during the Seven-Year War.
- 1598-1613: Russia descends into anarchy during the Time of Troubles.
- 1600: British East India Company chartered.

Significant people

British East India Company]
- Nicolaus Copernicus, developed the heliocentric (Sun-centered) theory using scientific methods (1473 - 1543).
- Henry VII of England, founder of the Tudor dynasty. Introduced ruthlessly efficient mechanisms of taxation which restored the kingdom after a state of virtual bankruptcy due to the effects of the Wars of the Roses (1457 - 1509).
- György Dózsa, leader of the peasants' revolt in Hungary (1470 - 1514)
- Michelangelo Buonarroti, Italian painter and sculptor (1475 - 1564).
- Thomas More, English politician and author (1478 - 1535).
- Martin Luther, German religious reformer (1483 - 1546).
- Hernán Cortés, Spanish Conquistador (1485 - 1547).
- King Henry VIII of England, founder of Anglicanism (1491 - 1547).
- King Francis I of France, considered the first Renaissance monarch of his Kingdom (1494 - 1547).
- Suleiman the Magnificent, Sultan of the Ottoman Empire. Conqueror and legal reformer (1494 - 1566).
- Charles V, Holy Roman Emperor and the first to reign as King of Spain. Involved in almost constant conflict with France and the Ottoman Empire while promoting the Spanish colonization of the Americas (1500 - 1558).
- Cuauhtémoc becomes last Tlatoani of the Aztec, leads the native resistance against the Spanish and is finally defeated in the siege of Tenochtitlan. He is hanged on February 26, 1525 (1502 - 1525)
- Mary I of England. Attempted to counter the Protestant Reformation in her domains. Nick-named Bloody Mary for her Religious persecution (1516 - 1558).
- King Philip II of Spain, self-proclaimed leader of Counter-Reformation (1527 - 1598).
- Queen Elizabeth I of England, central figure of the Elizabethan era (1533 - 1603).
- Oda Nobunaga , daimyo of the Sengoku period of Japanese civil war. First ruler of the Azuchi-Momoyama period (1534 - 1582).
- Toyotomi Hideyoshi , daimyo of the Sengoku period of Japanese civil war. Second ruler of the Azuchi-Momoyama period (1536 - 1598).
- Admiral Yi Sun-sin , respected as one of the greatest admirals and military leaders in world history. (1545 - 1598).
- Edward VI of England, notable for further differentiating Anglicanism from the practices of the Roman Catholic Church (1537 - 1553).
- Lady Jane Grey, Queen regnant of England and Ireland. Notably deposed by popular revolt (1537 - 1554).
- Queen Mary I of Scotland, First female head of the House of Stuart (1542 - 1587).
- Miguel de Cervantes, Spanish author (1547 - 1616).
- King Henry IV of France and Navarre, ended the French Wars of Religion and reunited the kingdom under his command (1553 - 1610).
- William Shakespeare, English author (1564 - 1616).
- John Donne, English metaphysical poet (1572 - 1631)
- Miyamoto Musashi, famous warrior in Japan, author of The Book of Five Rings, a treatise on strategy and martial combat. (1584 - 1645)
- Ahmad ibn Ibrihim al-Ghazi, Somali Imam and general (1507 - 1543).
- Ivan IV of Russia, first Russian tsar (1530-1584).

Inventions, discoveries, introductions

List of 16th century inventions
- The Columbian Exchange introduces many plants, animals and diseases to the Old and New Worlds.
- Introduction of the spinning wheel revolutionizes textile production in Europe.
- Modern square root symbol (√ )
- Copernicus publishes his theory that the Earth and the other planets revolve around the Sun (1543)
- Gregorian Calendar adopted by Catholic countries (1582)
- 1513: Juan Ponce de León sights Florida and Vasco Núñez de Balboa sights the eastern edge of the Pacific Ocean.
- 1519-22: Ferdinand Magellan and Juan Sebastián Elcano lead the first circumnavigation of the World.
- 1540: Francisco Vásquez de Coronado sights the Grand Canyon.
- 1541-42: Francisco de Orellana sails the length of the Amazon River.
- 1597: Opera in Florence by Jacopo Peri

Decades and years

Category:16th century Category:Centuries ko:16세기 ja:16世紀 th:คริสต์ศตวรรษที่ 16

Star

:This article is about celestial bodies. A star is a massive body of plasma in outer space that is currently producing or has produced energy through nuclear fusion. Unlike a planet, from which most light is reflected, a star emits light because of its intense heat. Scientifically, stars are defined as self-gravitating spheres of plasma in hydrostatic equilibrium, which generate their own energy through the process of nuclear fusion. Small (dwarf) stars such as the Sun generally have essentially featureless disks with only small starspots. Larger (giant) stars have much bigger, much more obvious starspots, and also exhibit strong stellar limb-darkening (the brightness decreases towards the edge of the stellar disk). Stellar astronomy is the study of stars.

Star formation and evolution

Star formation occurs in molecular clouds, large regions of high density in the interstellar medium (though still less dense than the inside of an earthly vacuum chamber). Star formation begins with gravitational instability inside those clouds, often triggered by shockwaves from supernovae or collision of two galaxies (as in a starburst galaxy). High mass stars powerfully illuminate the clouds from which they formed. One example of such a nebula is the Orion Nebula. Stars spend about 90% of their lifetime fusing hydrogen to produce helium in high-temperature and high-pressure reactions near the core. Such stars are said to be on the main sequence. Small stars (called red dwarfs) burn their fuel very slowly and last tens to hundreds of billions of years. At the end of their lives, they simply become dimmer and dimmer, fading into black dwarfs. However, since the lifespan of such stars is greater than the current age of the universe (13.6 billion years), no black dwarfs exist yet. As most stars exhaust their supply of hydrogen, their outer layers expand and cool to form a red giant. In about 5 billion years, when the Sun is a red giant, it will be so large that it will consume both Mercury and Venus. Eventually the core is compressed enough to start helium fusion, and the star heats up and contracts. Larger stars will also fuse heavier elements, all the way to iron, which is the end point of the process. Since iron nuclei are more tightly bound than any heavier nuclei, they cannot be fused to release energy. Likewise, since they are more tightly bound than all lighter nuclei, energy cannot be released by fission. In old, very massive stars, a large core of inert iron will accumulate in the center of the star. An average-size star will then shed its outer layers as a planetary nebula. The core that remains will be a tiny ball of degenerate matter not massive enough for further fusion to take place, supported only by degeneracy pressure, called a white dwarf. These too will fade into black dwarfs over very long stretches of time. white dwarf In larger stars, fusion continues until an iron core accumulates that is too large to be supported by electron degeneracy pressure. This core will suddenly collapse as its electrons are driven into its protons, forming neutrons and neutrinos in a burst of inverse beta decay. The shockwave formed by this sudden collapse causes the rest of the star to explode in a supernova. Supernovae are so bright that they may briefly outshine the star's entire home galaxy. When they occur within the Milky Way, supernovae have historically been observed by naked-eye observers as "new stars" where none existed before. Eventually, most of the matter in a star is blown away by the explosion (forming nebulae such as the Crab Nebula) and what remains will be a neutron star (sometimes a pulsar or X-ray burster) or, in the case of the largest stars, a black hole. The blown-off outer layers of dying stars include heavy elements which may be recycled during new star formation. These heavy elements allow the formation of rocky planets. The outflow from supernovae and the stellar wind of large stars play an important part in shaping the interstellar medium.

Appearance and distribution of stars

All stars except the Sun appear to the human eye as shining points in the nighttime sky that twinkle because of the effect of the Earth's atmosphere. Interferometer telescopes are required in order to produce images of these objects. The Sun is also a star, but it is close enough to Earth to appear as a disk instead, and to provide daylight. Stars are not spread uniformly across the universe, but are typically grouped into galaxies. A typical galaxy contains hundreds of billions of stars. The majority of stars are gravitationally bound to other stars, forming binary stars. Larger groups called star clusters also exist. Astronomers estimate that there are at least 70 sextillion (7×10²²) stars in the known universe [http://news.bbc.co.uk/2/hi/science/nature/3085885.stm]. That is 70 000 000 000 000 000 000 000, or 230 billion times as many as the 300 billion in our own Milky Way. The nearest star to the Earth, apart from the Sun, is Proxima Centauri, which is 39.9 trillion kilometers, or 4.2 light years away (light from Proxima Centauri takes 4.2 years to reach Earth). Travelling at the orbit speed of the Space Shuttle (5 miles per second -- almost 30,000 kilometers per hour), it would take about 150,000 years to get there. Distances like this are typical inside galactic discs, where the Sun and Earth are located. Stars can be much closer to each other in the centres of galaxies and globular clusters, or much further apart in galactic halos.

Age and size of stars

galactic halo Many stars are between 1 billion and 10 billion years old. Some stars may even be close to 13.7 billion years old, which is the observed age of the universe. (See Big Bang theory and stellar evolution.) They range in size from the tiny neutron stars (which are actually dead stars) no bigger than a city, to supergiants like the North Star (Polaris) and Betelgeuse, in the Orion constellation, which have a diameter about 1,000 times larger than the Sun—about 1.6 billion kilometers. However, these have a much lower density than the Sun. One of the most massive stars known is η Carinae, with 100–150 times as much mass as the Sun. Recent work by Donald Figer, an astronomer at the Space Telescope Science Institute in Baltimore, Maryland, suggests that 150 solar masses is the upper limit of stars in the current era of the universe. He used the Hubble Space Telescope to observe about a thousand stars in the Arches cluster, a massive young star cluster near the core of the Milky Way, and found no stars over that limit despite a statistical expectation that there should be several. The reason for this limit is not precisely known, but the Eddington limit is part of the answer. The very first stars to form after the Big Bang may have been larger, up to 300 solar masses or more, due to the complete absence of elements heavier than lithium in their composition. This generation of supermassive star is long extinct, however, and currently only theoretical. With a mass only 93 times that of Jupiter, AB Doradus C, a companion to AB Doradus A, is the smallest known star undergoing nuclear fusion in its core. Smaller bodies are brown dwarfs, which occupy a poorly-defined grey area between stars and gas giants. The minimum mass a star can have is estimated to be in the vicinity of 75 Jupiters.

Star classification

There are different classifications of stars ranging from type W, which are very large and bright, to M, which is often just large enough to start ignition of the hydrogen. Some of the more common classifications are O, B, A, F, G, K, M, and can perhaps be more easily remembered using the mnemonic "Oh, Be A Fine Girl, Kiss Me" (variant: change "girl" to "guy"), invented by Annie Jump Cannon (1863-1941). There are many other mnemonics for star classification; the most frequent addition tacks "Right Now, Sweetheart" for the red dwarf sub-types R, N and S. The new types L and T have also been recently appended to the end of the OBAFGKM sequence to classify the coldest low-mass stars and brown dwarfs, prompting such additions as "Lovingly Tonight" to the mnemonic. Each letter has 10 subclassifications. Our Sun is a G2, which is very near the middle in terms