A comet is a small body orbiting the sun on an elliptical path with a long tail of dust and ice.
Some comets are only visible by the aid of the telescope, while others can be seen by the naked eye. In the latter case they usually appear like stars accompanied with a train of light, sometimes short and sometimes extending over half the sky, mostly single and more or less curved, but sometimes forked. In a comet which appeared in 1744 the train was divided into several branches, spreading out from the head like a fan. The train is not stationary relatively to the head, but is subject to remarkable movements. The direction in which it points is always opposite to the sun, and as the , comet passes its perihelion the train changes its apparent position with extraordinary velocity. The head of the comet is itself of different degrees of luminosity, there being usually a central core, called the nucleus, of greater brilliancy than the surrounding envelope, called the coma.
Comets were long regarded as supernatural objects, and usually as portents of impending calamity. Tycho Brahe was the first who expressed a rational opinion on the subject, coming to the conclusion that the comet of 1577 was a heavenly body at a greater distance from the earth than that of the moon. The general law of the motion of bodies, as well as his own observations on the comet of 1680, led Isaac Newton to conclude that the orbits of the comets must, like those of the planets, be ellipses, having the sun in one focus, but far more eccentric; and having their aphelions, or greater distances from the sun, far remote in the regions of space.
This idea was taken up by Halley, who collated the observations which had been made of all the twenty-four comets of which notice had been taken previous to 1680. The results were very interesting. With but few exceptions the comets had passed within less than the earth's shortest distance from the sun, some of them within less than one-third of it, and the average about one-half. Out of the number, too, nearly two-thirds had had their motions retrograde, or moved in the opposite direction to the planets. While Halley was engaged on these comparisons and deductions the comet of 1682 made its appearance, and he found that there was a wonderful resemblance between it and three other comets that he found recorded - the comets of 1456, of 1531, and of 1607. The times of the appearance of these comets had been at very nearly regular intervals, the average period being between seventy-five and seventy-six years. Their distances from the sun, when in perihelion, or when nearest to that luminary, had been nearly the same, being nearly six-tenths of that of the earth, and not varying more than one-sixtieth from each other.
The inclination of their orbits to that of the earth had also been nearly the same, between 17 degrees and 18 degrees; and their motions had all been retrograde. Putting these facts together, Halley concluded that the comets of 1456, 1531,1607, and 1682 were reappearances of one and the same comet, which revolved in an elliptic orbit round the sun, performing its circuit in a period varying from a little more than seventy-six years to a little less than seventy-five; or having, as far as the observations had been carried, a variation of about fifteen months in the absolute duration of its year, measured according to that of the earth. For this variation in the time of its revolution Halley accounted upon the supposition that the form of its orbit had been altered by the attraction of the remote planets Jupiter and Saturn as it passed near to them; and thence he concluded that the period of its next appearance would be lengthened, but that it would certainly reappear in 1758 or early in 1759. As the time of its expected reappearance approached, Clairaut calculated that it would be retarded 100 days by the attraction of Saturn, and 518 by that of Jupiter, so that it would not come to the perihelion, or point of its orbit nearest the 500 sun, until the 13th of April, 1759.
It actually reached its perihelion on the 13th of March, 1759, being thirty days earlier than he had calculated. Along with the period of this comet and its perihelion distance, the magnitude and form of its path were also calculated. Estimating the mean distance of the earth from the sun at 95,000,000 miles (the number which was at that time considered as the true one), the mean distance of the comet was calculated to be 1,705,250,000 miles; its greatest distance from the sun, 3,355,400,000; its least distance, 55,100,000; and the transverse or largest diameter of its orbit, 3,410,500,000. This comet, therefore, is a body belonging to the solar system, and quite beyond the attraction of any body which does not belong to that system; and as this is determined of one comet, analogy points it out as being the case with them all. In 1835 it again returned, being first seen at Rome, on August the 5th, and from that time continued to be observed until the end of the year in Europe, and through a great part of spring 1836 in the southern hemisphere.
The comet denominated Encke's comet, which has made repeated appearances, was first observed in 1818, and was identified with a comet observed in 1786, also with a comet discovered in 1795 by Miss Herschel in the constellation Cygnus, and with another seen in 1805. Its orbit is an ellipse of comparatively small dimensions, wholly within the orbit of Jupiter; its period is 1260 days, or about three years and three-tenths. It has been frequently observed since.
Another comet, the history of which is of the utmost importance in the latest theories regarding the connection of these bodies and the periodic showers of shooting-stars, is one known as Biela's comet, discovered in 1826. It revolved about the sun in about 6.75 years, and was identified as the same comet which was observed in 1772 and in 1806. Its returns were noted in 1832, 1839, and 1845. In 1846 it divided into two, returned double in 1852, but has not since been seen, the Supposition being that it has been dissipated, and that it was represented by a great shower of meteors that were seen in November 1872. One of the most remarkable comets of recent times was that known as Donati's, discovered by Dr. Donati of Florence in 1858. It was very brilliant in England in the autumn of that year, and on the 18th of October was near coming into collision with Venus, The year 1881 was remarkable for the number of comets recorded. During that year no fewer than seven comets, including the well-known short-period comet Encke's, were observed. Research Comet
In a telescope, microscope, or other optical instrument, an eye-piece is the lens, or combination of lenses to which the eye is applied. Research Eye-Piece
The Renaissance was that change in the outlook of Europe which took place during the centuries from the fourteenth to the sixteenth. In its broadest sense the Renaissance affected every department of human life. But in its narrower sense it refers to the revival of the learning of ancient Greece, and to the effects of that revival on the arts and literature of modern peoples. The Church in the Middle Ages had taught men to revere authority and to find in her teaching an answer to all the problems of life, whereas the Greeks taught men to inquire and to explore rather than to accept, and to enjoy rather than to suffer. It was this attitude of mind, more than anything else, which shook the medieval world to its foundations. The views of the ancient Greeks, now re-born into the world, were in sharp contrast with the ideals of the Middle Ages. From these ideals many men for a time turned with a feeling of contempt.
The Renaissance was a many-sided movement: it deeply influenced learning and education, art and architecture, science and invention, geography and exploration, and, above all, religion. After the fall of Rome, a knowledge of Greek had rapidly died out in the West and no provision was made for its teaching similar to that made for Latin. In Italy, owing to the closeness of its relations with the East, the number of scholars, monks, and others, who learnt some Greek was greater than elsewhere. It is not, surprising, therefore, that the revival of learning received its main impulse from Italy. From the time of Petrarch and Boccaccio, Italian scholars became more and more devoted to ancient studies, and they began to visit Constantinople, where Greek learning had been preserved. There they hunted out, copied, and eagerly studied the precious manuscripts of the past, and these opened up a new world of thought. Further, from the time that the Turks' crossed from Asia into Europe, some of the Greeks themselves began to travel westwards and to accept well-paid teaching posts in the wealthy Italian cities. And, though the revival began in Italy, the new ideas were rapidly circulated by the new printing presses invented at the time, and every nation in due course played its part in the Renaissance.
The great and wealthy city of Florence was the centre of the Italian Renaissance. Cosimo de Medici, a merchant prince who became ruler of the city, was a patron of the New Learning, and he encouraged Greek scholars to settle in Florence. His grandson, Lorenzo de Medici, known as The Magnificent, loved to gather round him the learned men of the day; he spent 60,000 pounds a year on books; and he caused 200 rare manuscripts to be brought from the East to the Medici library. Rome was second only to Florence as a centre of the New Learning. The Popes themselves became great patrons of learning. Nicholas V founded the Vatican Library. When the son of Lorenzo de Medici became Pope as Leo X, the Renaissance in Rome reached its highest point. Leo made Rome, as he said, ' the capital of the world in literature, as it is in everything else'. He provided a hundred professors for his Greek college in Rome, and he brought his father's library to the Holy City. The library was afterwards restored to Florence by his cousin Clement VII, another member of this remarkable Medici family. The New Learning influenced England from the time of Edward IV, and it made great headway in the reigns of Henry VII and Henry VIII when the scholars known as the Oxford Reformers were flourishing.
The first Englishman to bring Greek manuscripts to England was William Selling. One of his pupils was Thomas Linacre, who went to Florence and shared the instruction given to the young Medici princes; he read in the Vatican Library, and made the acquaintance of Aldo at Venice. Another Oxford teacher who drew his inspiration from Italian sources was William Grocyn, one of the first men to give lectures on Greek literature at his University.
One of Grocyn's pupils was John Colet, who visited Italy in 1496 and returned to lecture on the Gospels in the Greek original at Oxford. He and Sir Thomas More, were friends of Erasmus, a Dutch scholar of international fame. Lady Margaret Beaufort, mother of Henry VII, was herself a patroness of the New Learning. She founded two Cambridge colleges, Christ's and St. John's, and two Lady Margaret Professorships of Divinity, one at Oxford and one at Cambridge. The Revival of Learning was one aspect of the Renaissance; the outburst of artistic energy in the fifteenth and sixteenth centuries was another. The painters of the new period broke away from the conventional art of the Middle Ages and began again to draw from living models. As with the artists, so with the sculptors. Donatello 'went straight with his mighty chisel to original sources - to youth and manhood, and the love of living'. The great figures of that age - Botticelli, Leonardo da Vinci, Michelangelo, Raphael, Titian - still dominate the history of European art. Examples of their works, and of many other Italian artists of the Renaissance, as well as of the Northern artists - Holbein, Durer, and others - are to be seen in the magnificent collection at the National Gallery.
It was natural that men who sought their inspiration from the Greeks should turn with renewed interest to classical architecture. The ruins of ancient Rome provided examples ready to hand; and soon churches planned like classical temples were rising in every city in Italy. St. Peter's, Rome, was designed by Bramante, and the famous dome added by Michelangelo. But great as was the enthusiasm for this architecture Renaissance architecture did not establish itself in England until the end of the reign of Queen Elizabeth I, though Henry VII's tomb at WestminsterAbbey is an example of the Florentine art of the period.
The Renaissance period, filled as it was with a love of experiment, naturally produced a renewed interest in science. With the exception of isolated geniuses like Friar Roger Bacon, there were no medieval scientists worthy of the name. Practically no scientific discoveries had been made for centuries. Modern Science begins its history with the Renaissance and owes a good deal to Leonardo da Vinci. He was the first of a long line of experimenters whose work has continued to the present day. The greatest shock to the medieval notions of the universe was given by Copernicus. For two thousand years mankind with few exceptions had believed that the earth was the centre of the universe, and that the sun revolved round our planet every twenty-four hours. Such had been the teaching of Ptolemy, the Greek scientist. Another Greek, Pythagoras, had questioned it, and advanced the extraordinary notion that the sun, not the earth, was the centre of the universe; but there were few who accepted his theory until Copernicus turned his attention to the 'solar system'. Through slits cut in the walls of his house, Copernicus watched the movements of the planets. Just before he died in 1543 he published a book - 'The Revolutions of the Heavenly Bodies' - giving to the world the results of his observations.
Twenty years later the famous Galileo was born at Pisa, and it was he who perfected the telescope. He lived to popularise the theory of Copernicus, but he was nearly put to death for his pains and was forced by the Court of Inquisition to recant. The Italian Galileo, and the English Newton who discovered the laws of gravity, were the two greatest scientists of the seventeenth century. In the realm of geographical discovery, no age in the world' s history was more momentous than the Age of the Renaissance. Columbus, who discovered America; Vasco De Gama, who found the Cape Route to India; Cabot, Cartier, and Cortez, the discoverers of Newfoundland, Canada, and Mexico; Balboa, who first sailed on the Pacific; Magellan, whose ship was the first to sail round the world - all these and many more make the fifteenth and sixteenth centuries an era without parallel in the annals of discovery.
The new ideas which came surging into the world during the Renaissance acted in many respects as disruptive forces. This was particularly true in the realm of religion. An unquestioning acceptance of authority - i.e. of the teaching of the Catholic Church - was the keynote of the medieval attitude to life, but an eager, inquiring generation began to question this attitude. Men, too, were shocked by the moral decay of the Church and of the Papacy; voices were raised demanding reforms. Some reformers, like Colet and Erasmus, tried to reconcile the new ideas with the Church of Rome and worked to reform it; others, of whom Luther was the greatest, rejected altogether its authority.
The revolution in European history known as the Reformation was an indirect result of the Renaissance - of the New Learning which invited comparison between the present and the past; of the invention of printing which scattered broadcast the new ideas; and again, of the growing idea of the Nation and with it the supremacy of the State. Research Renaissance
Telescopium, the Telescope, is a constellation of the southern sky, between Ara and Sagittarius, named by the 18th-century French astronomer Nicolas Louis de Lacaille. Its brightest stars are of only fourth magnitude and it is devoid of interesting objects apart from a few faint galaxies, an unremarkable globular cluster, and a small planetary nebula. Research Telescopium
Galileo Galilee was an Italian physicist. He was born in 1564 at Pisa and died in 1642. The son of a Florentine nobleman, his father intended him to go into medicine and procured for him an excellent education in literature and the arts, and in 1581 he entered the University of Pisa.
At nineteen the swinging of a lamp in Pisacathedral led him to investigate the laws of the oscillation of the pendulum, which he subsequently applied in the measurement of time; and in 1586 the works of Archimedes suggested his invention of the hydrostatic balance. He now devoted his attention exclusively to mathematics and natural science, and in 1589 was made professor of mathematics in the University of Pisa.
In 1592 he was appointed professor of mathematics in Padua, where he continued eighteen years, and his lectures acquired European fame. Here he made the important discovery that the spaces through which a body falls, in equal times, increase as the numbers 1, 3, 5, 7. If he did not invent he improved the thermometer, and made some interesting observations on the magnet. To the telescope, which in Holland remained not only imperfect but useless, he gave a new importance. He noted the irregularity of the moon's surface, and taught his scholars to measure the height of its mountains by their shadow.
A particular nebula he resolved into individual stars, and conjectured that the Milky Way might be resolved in the same manner. His most remarkable discovery was that of Jupiter's satellites in 1610, and he observed, though imperfectly, the ring of Saturn. He also detected the sun's spots, and inferred, from their regular advance from east to west, the rotation of the sun, and the inclination of its axis to the plane of the ecliptic.
In 1610 Cosmo II, grand-duke of Tuscany, appointed him grand-ducal mathematician and philosopher, and with increased leisure he lived sometimes in Florence, and sometimes at the country seat of his friend Salviata, where he gained a decisive victory for the Copernican system by the discovery of the varying phases of Mercury, Venus, and Mars. In 1611 he visited Rome for the first time, where he was honourably received; but on his return to Florence he became more and more involved in controversy, which gradually took a theological turn.
The, monks preached against him, and in 1616 he found himself again obliged to proceed to Rome, where he is doubtfully said to have pledged himself to abstain from promulgating his astronomical views. In 1623 Galileo replied to an attack upon him in his Saggiatore, a masterpiece of eloquence, which drew upon him the fury of the Jesuits. In 1632, with the permission of the pope, he published a dialogue expounding the Copernican system as against the Ptolemaic. A congregation of cardinals, monks, and mathematicians, all sworn enemies of Galileo, examined his work, condemned it as highly dangerous, and summoned him before the tribunal of the Inquisition. The veteran philosopher was compelled to go to Rome early in 1633, and was condemned to renounce upon his knees the truths he had maintained. At the moment when he arose, he is said (but this is doubtful) to have exclaimed, in an undertone, stamping his foot, 'E pur si muove!' (and yet it moves!). Upon this he was sentenced to the dungeons of the Inquisition for an indefinite time, and every week, for three years, was to repeat the seven penitential psalms of David. After a few days' detention his sentence of imprisonment was commuted to banishment to the villa of the Grand-duke of Tuscany at Rome, and then to the archiepiscopal palace at Sienna.
He was afterwards allowed to return to his residence at Arcetri, near Florence, where he employed his last years principally in the study of mechanics and projectiles. The results are found in two important works on the laws of motion, the foundation of the present system of physics and astronomy. At the same time he tried to make use of Jupiter's satellites for the calculation of longitudes; and though he brought nothing to perfection in this branch, he was the first who reflected systematically on such a method of fixing geographical longitudes. He was at this time afflicted with a disease in his eyes, one of which was wholly blind and the other almost useless, when, in 1637, he discovered the libration of the moon.
Domestic troubles and disease embittered the last years of Galileo's life. After his death his remains were ultimately deposited in the church of Sta. Croce, at Florence. Research Galileo
James Gregory was a Scottish mathematician and the inventor of the reflecting telescope. He was born about 1638 at Drumoak, in Aberdeenshire and died in 1675. He received his education at Marischal College and in 1663 he published Optica Promota, explaining the idea of the telescope which bears his name. He spent some years in Italy, and published at Padua in 1667 a treatise on the Quadrature of the Circle and Hyperbola. He became professor of mathematics at St Andrews in 1668, and at Edinburgh in 1674, but died suddenly in 1675.
James Gregory was a Scottish physician. He was born in 1753 at Aberdeen and died in 1821. The eldest son of John Gregory, he studied medicine at Edinburgh, and in 1776 was appointed professor of the institutes of medicine. In 1780-82 he published his Conspectus Medicinae Theoreticae; in 1790 became professor of the practice of physic, and in 1792 issued his Philosophical and Literary Essays. Research James Gregory
John Gregory was a Scottish physician. He was born in 1724 and died in 1773. The grandson of James Gregory, the inventor of the reflecting telescope, he was successively professor of philosophy and medicine in King's College, Aberdeen, and of the practice of physic at Edinburgh. His works include Elements of the Practice of Physic, a Comparative View of the State and Faculties of Men and Animals, and A Father's Legacy to his Daughters. Research John Gregory
Sir William Herschel was an Anglo-German astronomer. He was born in 1738 and died in 1822. He discovered the planetUranus. The son of a Hanoverian musician, he came to England in 1757, and was employed in the formation of a military band, and in conducting, while organist at Bath, several concerts, oratorios, etc.
Although enthusiastically fond of music, he had for some time devoted his leisure hours to the study of mathematics and astronomy; and being dissatisfied with the only telescopes within his reach, he set about constructing instruments for himself. Late in 1779 he began a regular survey of the heavens, star by star, with a 7-feet reflector, and discovered, on March the 13th, 1781, a new primary planet, named by him the Georgium Sidus, but now known as Uranus. This discovery extended his fame throughout the world, and brought him a pension of 400 pounds a year, with the title of private astronomer to the king.
Assiduously continuing his observations, he measured the rotation of Saturn, discovered two of its satellites, and observed the phenomena of its rings. He also discovered the satellites of Uranus, and observed the volcanic structure of the lunar mountains. At Slough, near Windsor, he erected a telescope of 40 feet length, and completed it in 1787.
William Herschel received much assistance in making and recording observations from his sister Caroline Herschel and latterly his brother, a skilful optical instrument maker, lent him valuable aid. In 1802 he laid before the Royal Society a catalogue of 5000 nebulse and clusters of stars which he had discovered. He was made DCL by the University of Oxford, and in 1816 was knighted. Research William Herschel
William Parsons, the third earl of Rosse, was an English astronomer. He was born in 1800 at York and died in 1867. He was member of parliament for King's County, Ireland from 1823 to 1834, but resigned to devote time to improving reflecting telescopes. His great telescope was erected at Parsonstown in King's County in 1845. Research William Parsons
Abbreviations
Research Comet
