Interesting Astronomical Information

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Amidst the glare of the Sun is a tiny speck... Earth

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Ancient AstronomersConstellationsPtolemyCopernicusBraheKeplerGalileo

Ancient Astronomers

Ancient Astronomers

The Ancient Greeks made the first great advances in astronomy. In their observations of the heavens a The Ancient Greeks made the first great advances in astronomy. In their observations of the heavens a succession of brilliant thinkers used geometrical principals rather than supernatural beliefs to explain what they saw. In doing so they began to break the link between astronomy and astrology. However for many centuries astronomy remained the most abstract of the natural sciences. Fascinated with the regularity of the heavens, early astronomers took to studying the motions of the heavenly bodies and in the course of time built up a fair knowledge of the movements of the stars although they knew nothing of their true nature.

The Greek philosopher, Thales of Miletus (624 BC-546 BC in what is today the Aydin Province of Turkey) is credited as having been the first scientist. He proposed that the world was made of water and that the Earth was a flat disc that floated on the water. He seems to have been the original absent minded professor and a tale was told of him falling down a well while wandering along looking up at the stars.

Although Thales was thought of as being an impractical dreamer he correctly predicted that weather conditions for the year ahead would bring a good olive harvest, bought up all the olive presses in the district and made a fortune from his monopoly of the market. The influential philosopher Pythagoras of Samos (569 BC- 475 BC) was the first to envisage the Earth as a spherical ball. Around it the Sun, Moon and all the planets revolved in concentric circles, each attached to a sphere which kept it in motion. Heraclides of Pontus (387 BC-312 BC) hypothesized that the Earth rotated on its axis once every 24 hours, an idea that did not become widely accepted for many hundreds of years.

With Aristotle (384 BC-322 BC) the Earth centered concept of the universe gained new strength, even though there were formidable obstacles to be overcome. The Greeks had already noted that the planets moved eastward in a very peculiar fashion, occasionally reversing direction and heading west. Aristotle believed that the Earth was surrounded by a series of concentric crystal spheres, the outermost carrying the fixed stars while inner spheres carried the planets Saturn, Jupiter and Mars followed by the Sun's sphere and by the spheres of Venus, Mercury and closest to the Earth, the Moon. He proved that the Earth was spherical by pointing out that it cast a circular shadow on the Moon and that individual stars appear to move higher or lower above the horizon the further north or south you traveled.

Aristarchus of Samos (310 BC-230 BC) followed Heraclides in believing that the apparent daily rotation of the fixed stars was due to the rotation of the Earth on its axis. He is mostly remembered as the first to propose a Sun-centered universe which was larger than any of the Earth centered models proposed by his predecessors and anticipated the ideas of Copernicus by 1,900 years. An attempt to measure the distances to the Sun and Moon was made by Aristarchus and he came to the conclusion that the Sun was 19 times more distant than the Moon. Even though this was terribly inaccurate it represents the first step towards an appreciation of the size of the universe.

The Greeks however were not simply content to describe celestial phenomena and devise theories. They were also eager to measure the circumference of the Earth and the distances to the planets and stars. Eratosthenes of Cyrene (276 BC-194 BC) using very simple methods came remarkably close to our present day figures. Noticing that the Sun at midday on June 21st cast no shadow at Syene (now Aswan in Egypt) but an obelisk in Alexandria, a distance of 5,000 stadia to the south, cast a measurable shadow he was able to determine just what fraction of the earths circumference was represented by the distance between these two locations. He calculated the Earth's circumference to be 250,000 stadia or 42,160 km, only slightly larger than today's figure of 40,075 km.

Hipparchus of Rhodes (190 BC-120 BC) the brilliant Greek astronomer is best remembered for his creation of instruments used in making astronomical measurements. He was able to establish the first realistic distances to the Sun and the Moon. By observing eclipses of the Moon and noting how long it took to pass through the Earth's shadow he determined that the distance to the Moon was equal to 29.5 Earth diameters, very close to today's figure of 30 Earth diameters. He measured the length of the year to an accuracy of 6.5 minutes, discovered the slow change in direction of the axis of rotation of the Earth and produced a star atlas containing 850 stars categorized by their brightness. It is truly fitting that the European Space Agency's satellite launched in 1989 carried his name. It has been used to make precise measurements of the position and motion of over one hundred thousand stars. Astronomers analyzed the data collected by the satellite and the resulting catalogue, available in hard copy or as a 6 disc set, has also been named for him.

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The Constellations


The sky is divided into 88 sections, known as constellations, which simplify the locating and naming celestial objects. The main constellations of the sky were devised at the dawn of history by Middle Eastern people who imagined that they could see a likeness to certain fabled creatures and mythological heroes among the stars.

The largest constellation in the sky is Hydra-The Water Snake which winds its way over 100 degrees of the sky. It is by no means easy to identify on account of its faintness and apart from its brightest star Alphard, which marks the heart of the water snake, the only other recognizable feature is its head, made up of an attractive group of six stars lying just south of the constellation Cancer-The Crab. The smallest of the constellations is Crux-The Southern Cross which is one of the most recognizable and celebrated constellations in the heavens. Very few constellations look like the creature or object that they are named for but they are mainly meant to honor, not represent.

Our Modern constellations derive from a list of 48, recognized by the Greek astronomer Ptolemy in 150 AD. This list was expanded on by navigators and celestial map makers, notably the German Johann Bayer (1572-1625), the Pole Johannes Hevelius (1611-1687) and the Frenchman Nicolas Louis de Lacaille (1713-1762). Lacaille introduced 14 new constellations, named after instruments used by scientists and artists, in parts of the southern sky not visible from Mediterranean regions; other astronomers invented constellations to fill in the gaps between the figures recognized by the Greeks. The whole process sounds rather arbitrary, and indeed it was. A number of the newly devised patterns fell into disuse, leaving a total of 88 constellations that were officially adopted by the International Astronomical Union, astronomy's governing body, in 1930. Some of the brighter stars have proper names and these names are mainly of Arabic origin. The stars in each constellation are also labeled with a letter of the Greek alphabet, the brightest star usually (though not always) being termed (alpha). Notable exceptions include the constellations Gemini and Orion in which the brightest stars are in fact marked  (beta) and because of the breaking up of the ancient constellation Argo Navis-The Ship into three smaller constellations, two of the resulting constellations namely Vela-The Sails and Puppis-The Stern have no alpha or beta stars.

There is no need to learn all of the constellations visible from your location on the Earth but learning to recognize some of the more familiar ones will be a great help in finding your way around the night sky. The more you look the more you will see and the greater will be your enjoyment of the magnificent starry spectacle. There are books available from the observatory or from good book shops that will help you to navigate and become familiar with the star patterns and will open up a whole new relaxing pastime.

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Astronomy, by its very nature, touches on the most sacred mysteries of creation and for thousands of years this science has fascinated the minds of men. Astronomy's roots probably lie in the stargazing done by our ice age ancestors some 30,000 years ago who foretold the changes in the seasons by the changes in the sky. In his total ignorance of the stars and the reasons for their revolutions he realized that the hours and the seasons depended upon the course of these distant lights. In the 600 years leading up to the birth of Christ the interest in solving the mysteries of the Universe began to gain momentum and many great scholars and philosophers were working toward finding the answers.

One such speculator was the Greek mathematician and astronomer Claudius Ptolemaios, known simply as Ptolemy. Both his exact birth date and the date of his death are not certain but it seems that he was born around AD 85 in Egypt and died around AD 165 in Alexandria where it appears he spent his entire life. Very little information about his early life has survived the years and historians are not even sure whether he was Greek or Egyptian. Strong evidence favours a Greek heritage as he was born Ptolemais Hermii, both names of Greek origin. To also complicate matters he, or one of his ancestors, was granted citizenship of Rome, hence the name Claudius.

Although Ptolemy is better remembered for his work in astronomy he also dabbled in astrology. In a four volume book Tetrabiblios, he attempted to show how patterns in the stars could influence human events. Optics and geography were two other sciences in which he was involved, composing tables for the refraction of light as it passed into water at different angles. His maps and tables of latitude and longitude, although based on a much too small estimate of the size of the Earth, appeared in another of his books entitled Geography. In one of his later writings he attempted to calculate the distances to the Sun, Moon and planets but unfortunately very little of this work has survived to the present day.

Ptolemy's model of the universe attempted to explain the observed motions of the Sun, Moon and planets and predict their future positions. He was instrumental in collating all the recorded observations of his predecessors, especially those of Hipparchus, and combining them to produce his own Earth centered model of the universe. He developed a detailed mathematical theory to predict the movements of the heavenly bodies. His work was published in a book now known by its Arabic title of Almagest (The Greatest). As Ptolemy and most of antiquity's astronomers saw it, the perfect bodies in the heavens had to follow the only perfect shape, a circle. His system therefore demanded that all celestial objects moved at a constant speed in circular orbits. Even course observations showed this not to be the case so he gave his orbits epicycles, smaller circular orbits on the rim of the main orbit. These epicycles then accounted for the sometimes backward motion of the planets against the background stars. His cosmic model made remarkably accurate predictions and after all that was what the early astronomers were chiefly seeking. Despite the flaws inherent in this system, it was held as truth until Nicholas Copernicus came along with a new theory in 1543, placing the Sun at the centre of the planets. Ptolemy has a crater on the Moon named after him and also an asteroid bears his name.

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Nicholas Copernicus


Often referred to as the father of modern astronomy, Nicholas Copernicus was born on February 19th 1473 in the Polish town of Torun. Following the death of his father when he was only ten years old, the young Copernicus was taken under the protective wing of his highly influential maternal uncle. At the age of 18, he entered the University of Kracow which was then the capitol of the kingdom of Poland where he studied mathematics, astronomy, philosophy, Latin and optics. In 1496 he moved to Italy where he studied arts at Bologna, medicine at Padua and law at the University of Ferrara from which he graduated in 1503 with a doctorate of canon law. He then returned to Poland to the cathedral at Frauenberg which was less than 160 kilometers from his birth place and where he spent a sheltered life for most of the rest of his days.

The fundamental question on which Copernicus diverged from Ptolemy, whom he revered as his most exalted predecessor, was the cosmological status of the Earth. For Ptolemy, the Earth was not a heavenly body; the stars and planets all moved around the Earth but the Earth stood still. Copernicus clearly saw and explicitly stated that the Earth was a heavenly body, a planet of the Sun, and in constant motion around the Sun. There was nothing new in Copernicus' announcement of these ideas as they had been speculated in antiquity by Aristarchus in his treatise "On the Size and Distance of the Sun and Moon", of which a copy still survives today. But Aristarchus had merely formulated the bare ideas without offering any proof or elaboration. Copernicus on the other hand had come up with his deductions by meticulous observations which he carried out quietly and alone from a tower on the outer wall of the cathedral. All of his observations were made with the naked eye as the telescope would not be invented until over one hundred years later.

What is night, and how is it produced? The explanation, according to the ideas prevailing before Copernicus, was that the Sun circled the Earth and after rising in the east in the morning and passing nearly overhead at noon, dropped down to the west in the evening and then went beneath us to produce night. Copernicus however considered the Sun to be completely at rest. Hence night occurs at those places where, as our planet rotates on its axis once every 24 hours, the light which is perpetually streaming from the Sun is cut off by the opaque bulk of the Earth itself. In 1530 Copernicus completed his work "De Revolutionibus" whose title may be translated as "Concerning the Revolutions of the Heavenly Spheres", in which he asserted that the Earth rotated on its axis once daily and traveled around the Sun once in a year.

This was a fantastic concept for the times and completely against the thinking of the church. Because of this and the fact that he was a perfectionist and thought that the work could somehow be improved with more observations, he was reluctant to put it into print. He was finally persuaded to publish it by one of his students and enthusiastic supporter, George Rheticus who took it to the printer Johann Petreius in Nurnberg late in 1541. Copernicus received a copy of the printed book, consisting of 200 pages and written in Latin, for the first time on his death bed. Less than 24 hours after touching the book he was dead. He died of a cerebral haemorrhage on May 24th 1543.

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Tycho Brahe


Born on December 14th 1546 at Knutstorp in Denmark, Tycho Brahe was one of twins but his brother died shortly after birth. His father Otte was a nobleman and an important figure at the court of the Danish king and his mother also came from an important family. When he was only two he was abducted by his uncle Jorgen Brahe and his wife Inger who were childless. This strange event appears to have caused no family upheaval and his real parents seem to have made no attempt to get him back. Jorgen and his wife acted as foster parents until Jorgen's death in 1563. He began his studies at the University of Copenhagen on April 19th 1559 where he studied law and philosophy and took only a slight interest in astronomy. It seems that a predicted partial solar eclipse of the sun on August 21st 1560 sparked in him a real astronomical interest.

In February 1562 Tycho set off for the University of Leipzig taking with him his newly acquired astronomy books and constellation charts. By August 1563 he was making serious observations of his own of the sky and keeping accurate records of these observations. Previously constructed tables of a conjunction of Saturn and Jupiter failed to predict the correct date of the event and though still only 16 years of age he thought that he could do better. He came up with a model of the solar system which was different to both the systems of Ptolemy and Copernicus. In Tycho's solar system the Sun orbited the Earth while all the other planets orbited the Sun. When he was 20 at the University of Rostock at which he enrolled in 1566 he got into an argument with another student about who was the best mathematician and in the ensuing duel he had the bridge of his severed. For the rest of his life he wore a prosthesis made of silver and gold held in place with paste. He appears to have been quite eccentric and later in his life kept a dwarf named Jepp as a court jester who he thought was clairvoyant and who would sit under the table during dinner.

Returning home in 1570 he met Kirsten Jorgensdatter who became his common law wife and with whom he had eight children. She stayed with him until his death thirty years later. Early in the evening of November 11th 1572 an event occurred that was to change his whole life. Glancing overhead into the early evening sky he noticed a new bright star had appeared in the constellation Cassiopeia. He was not the first to see this new star, (which we know today to have been an existing star that exploded and referred to as a supernova), but his observations of it over several months proved that it did not move in relation to the other stars and so was indeed no closer to the earth than the other stars. According to the prevailing world view and sanctified by the church the heavens were eternal and unchanging. With the appearance of this new star the concept of an unchanging universe was destroyed forever and the use of observation to settle arguments was the birth of modern astronomy. Tycho published an account of the new star in "De Stella Nova" in 1573 and it brought him great fame and favour with the king of Denmark, Frederic II.

In February 1576 the king granted him the small 2,000 acre island of Hven on which to build an astronomical observatory. The funds were forthcoming to build the observatory and all the instruments he would need for his observations. He called the observatory Uraniborg, Castle of the Heavens, and from here most of his observations of the heavens were conducted. Over one hundred students found their way to his doors from 1576 to 1597 and with a total of 28 instruments his measurements of star and planetary positions were unparalleled in accuracy for their time. During this time he published a star catalogue containing the position of 1,004 stars. After the death of King Frederic II Tycho had a falling out with the new king, Christian IV and he moved to a new observatory in Benatky, fifty kilometers from Prague where he continued his observations for another year before moving to Prague. He was appointed Imperial Mathematician to the Holy Roman Emperor, Rudolph II in 1599 and it was then, on the first day of the year 1600 that Johannes Kepler joined him as an assistant. With Kepler's help he compiled a new set of astronomical tables based on his observations over the past thirty eight years and after Tycho's death Kepler was able to use the tables to deduce his own laws of planetary motion.

Tycho Brahe died on October 24th 1601 of ureamia, urine in the blood, the consequence of too much drinking at a banquet. Etiquette forbade him to leave the dinner table to relieve himself before his host had finished eating. In a state of delirium on the night before he died he muttered over and over again "Let me not seem to have lived in vain".

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Johannes Kepler


Kepler, according to his own horoscope, was conceived on May 16th 1571 at 4:37am and born prematurely December 27th at 2:30pm. He was born in the town of Weil in Swabia a south western corner of Germany between the Black Forest, the Neckar and the Rhine. His father, Heinrich was a mercenary adventurer who narrowly escaped the gallows and his mother Katherine was brought up by an aunt who was burned alive as a witch. Johannes was a sickly child and suffered from boils, rashes and piles and his gall bladder gave him constant trouble. He was also born with defective eyesight, myopia and double vision.

Kepler attended the theological seminary from the ages of thirteen to seventeen where he studied Greek, Latin, mathematics, music and philosophy. His fellow students regarded him as an intolerable egghead and beat him up at every opportunity. He was quite superstitious and delved into astrology, very often doing his own horoscope. After graduating from the Faculty of Arts at the University of Tuebingen at the age of twenty he went on to study for another four years at the Theological Faculty in pursuit of his chosen profession as a clergyman. However before he was to pass his final exams he was offered the post of a teacher of mathematics and astronomy in Gratz, the capitol of the Austrian province of Styria. He had never thought of becoming an astronomer but had been interested in the mystical Copernican implications of a Sun centered universe. After some hesitation he accepted the position and arrived in Gratz in April 1594 at the age of twenty three. He was not a good lecturer as his lectures were rambling and disjointed and during his first year had only a handful of students and in his second year had none at all. However the directors of the school did not blame him for the lack of students, as they believed "the study of mathematics was not every man's affair".

Kepler's first book, "The Mysterium Cosmographicum", contains the seeds of his principal future discoveries. In it appeared the first public commitment, by a professional astronomer, to the Copernican Sun centered universe and appeared fifty years after the death of Copernicus. Galileo, Kepler's senior by six years, was still silent on Copernicus and agreed with him only in cautious privacy. Kepler had many strange theories on the workings of things from the idea that the universe was built around five perfect solids, the tetrahedron (bound by four equilateral triangles), the cube, the octahedron (eight equilateral triangles), the dodecahedron (twelve pentagons) and the icosahedron (twenty equilateral triangles) to the idea that the universe was governed by musical harmonies. It seems he was never afraid to ask questions no matter how foolish they seemed and he is quoted as remarking "If my false figures come close to the facts this happened merely by chance yet it gives me pleasure to remember how many detours I had to make, along how many walls I had to grope in the darkness of my ignorance until I found the door which lets in the light of truth". As he got older he slowly changed from the restless student who had never been able to finish what he started into a scholar with a great capacity for work, for physical and mental endurance and fanatical patience unequaled in the annuls of science.

Johannes Kepler's first marriage took place when he was twenty five years old on April 27th 1597 to Barbara Muehleck, described by Kepler himself as "simple of mind and fat of body who was stupid, sulking, lonely and often taken to fits of melancholy. She was of an angry nature, constantly ill and deprived of her memory". She was the daughter of a rich mill owner who was reluctant to give his daughter up to the likes of Kepler, a man of such lowly standing and miserable pay, and it took long and persistent negations by Kepler's friends before he relented and agreed to the marriage. She bore him five children but only two survived, the other three dying after only a few months of cerebral meningitis. After fourteen years of marriage Barbara also died at the age of thirty seven.

It was around the time of the death of his wife that his book, Mysterium Cosmographicum came out and he was obliged to buy the first two hundred copies to compensate the printer for his work. He sent copies to many scholars of the day including Galileo and Tycho Brahe. He began to take on many projects among them the existence of stellar parallax, investigations into the Moon's orbit, Magnetism, research into optics and he started a weather diary which he kept for thirty years. His main focus however was on his search for a mathematical law to explain the harmony of the spheres and the movement of the planets.

His theories on the harmonies of the spheres of the Pythagorean musical scale and a combination of both did not quite fit the facts and Kepler knew that there was only one man in the world who had the figures that he needed: Tycho Brahe. But Tycho refused to publish his observations until he had completed his own theory and he carefully guarded his volumes of figures, the result of a lifetime of work. Kepler was extremely jealous of Tycho's observatory in Uraniborg and he wrote "Any single instrument of his cost more than my whole family's fortune put together". In his opinion Tycho was superlatively rich but did not know how to put his riches to proper use and so it was fair that he should try to wrest those riches from him. These opinions were stated twelve months before he had actually met Tycho and before Tycho, in a letter to Kepler, had expressed the desire to someday meet him. Kepler however could not afford the trip and it was only by good fortune that a year later he was offered passage from Gratz to Prague with Baron Hoffman. The date that he left Gratz for his meeting with Tycho was January 1st 1600.

His first meeting with Tycho occurred on February the 4th 1600 and over the next two months he stayed as a guest, analyzing some of Tycho's observations of Mars. Although Tycho was impressed by Kepler's theoretical ideas he still would not allow him full access to his observations and Kepler became disillusioned and the two had an argument during which Kepler threatened to return home. They soon settled their differences however and Kepler was offered a salary and living conditions to his satisfaction. In June he left for Gratz to collect the rest of his family. Because of political unrest he was not able to return to Tycho until the last months of 1600 and was immediately put to work analyzing Tycho's planetary observations. Tycho Brahe died unexpectedly on October 24th 1601 and two days later Kepler was appointed as his successor as Imperial Mathematician and with Tycho's death he now had access to all of Tycho's Mars observations. Using these observations he was able to come up with his three laws pertaining to the motion of the planets. The first law states that "All the planets move in ellipses with the Sun at one focus, the other being vacant". The second law states, "The planets sweep out equal areas at equal times" and the third law states "The square of the periodic times are to each other as the cubes of their average distances".

In October 1610 a bright new star appeared in the Milky Way in the constellation of Ophiuchus and Kepler began systematic observations of it and noting its fading brightness over the following months. This star had used up most of its hydrogen and exploded as a supernova but to the astronomers of Kepler's time they were a complete mystery. In his book "De Stella Nova" he argues that because of the lack of parallax the object must indeed be in the realm of the fixed stars and that the heavens were not unchanging, further undermining the doctrine of the church.

In the first months of 1610 the Italian astronomer Galileo used his telescope to observe the moons of Jupiter and sought the opinion of Kepler to enhance the credibility of his observations. Using a telescope he borrowed from the Duke of Cologne Kepler made his own observations of Jupiter and published his own findings which backed up the observations of Galileo. He was however disappointed when Galileo failed even to acknowledge his efforts.

Kepler married twenty four year old Susanna Reuttinger on October 30th 1613 and this appears to have been a happier marriage than his first. They had six children, the first three dying in childbirth and the last three surviving into adulthood. He spent the rest of his life studying the motion of the planets and indeed modern astronomy owes him a great deal. Kepler wrote towards the end of his life "The roads by which men arrive at their insights into celestial matters seem to me to be almost as worthy of wonder as those matters themselves". He died at Regensburg on November the 15th 1630 and was buried there. His burial sight was lost however after the armies of Gustavus Adolphus destroyed the churchyard in which he was interred. There has been a crater on the Moon, a crater on Mars and an asteroid named in his honour and on March the 6th 2009 NASA launched the Kepler Mission, a space telescope designed to search for Earth like planets around other stars.

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Galileo Galilei


Probably the best known of the ancient astronomers, Galileo Galilei was born in the town of Pisa in Italy on the 15th of February 1564, the first of six children. His family moved to Florence in 1572 but Galileo remained in Pisa and from the ages of eight to ten went to live with Muzio Tedaldi who was related to his mother by marriage. He was reunited with his family in Florence in 1574 where he was privately tutored by Jacopo Borghini. When he was old enough he was sent to the monastery at Vallambrosa and was educated by the monks until 1581 when he enrolled in the University of Pisa to study Medicine. It seems that he was not too serious about his medical studies and persuaded his father to let him study Philosophy and Mathematics. However in 1585 he left the University without attaining a degree. Then followed four years of private tutoring after which he returned to the University of Pisa as a Professor of Mathematics in 1589.

With the death of his father in 1591 Galileo became the financial provider in the family but his salary at Pisa was not enough to support them all. He applied for and was appointed Professor of Mathematic at the University of Padua, where he remained until 1610, on a salary that was three times that of his previous income. It was during these years at Pisa and Padua that Galileo began his experiments on the properties of falling bodies. He was able to prove that objects dropped from a tower fell at the same rate regardless of their weight. His inventions included the microscope and an early version of the thermometer and the calculation of the parabolic path of projectiles and the study of the motion of pendulums were also problems he put his mind to solving. Galileo was only mildly interested in astronomy up to this point in his life but it is known from letters written to Johannes Kepler in 1598 that he subscribed to the Copernican system of the Sun centered model of the universe. Between the years 1600 and 1606 he fathered three children, two daughters and a son, to his life partner, Maria Gamba, whom he never married.

In May of 1609 Galileo heard of a spyglass that had been invented by a Dutchman, Hans Lippershey, which showed distant objects to appear much closer than they actually were when viewed through this instrument. From descriptions he received of the device he was able to use lenses that were available to him at the time to make his own version of it, the first one giving him a magnification of three to four times. Over the next few months he constructed several telescopes with lenses that he ground himself and by August of the same year had made an instrument that gave a magnification of nine times. His instrument was much improved on the Dutch version and he was soon requested to give a demonstration of it to the Venetian Senate. They were most impressed with his efforts and he was granted a substantial increase in his salary, after giving the senate sole rights to manufacture more of the instruments. The senate soon realized that the rights to manufacture the telescopes that Galileo had given them were worthless, as he was not the inventor, and froze his salary altogether. Luckily for Galileo he had also sent one of his instruments to the Grand Duke of Tuscany, Cosimo de Medici, who granted him the position of "Mathematician and Philosopher" to the Grand Duke and Chief Mathematician at the University of Pisa.

Before the year 1609 was out, Galileo had turned his telescope to the night sky. In the months of December 1609 and January 1610 he was to make more discoveries that changed the thinking of the world than anyone had made before or has been made since. Aristotle had said that everything in the universe was perfect and spherical but when Galileo looked at the Moon through his telescope he could see that it was rough and uneven. On January 7th 1610 he looked at the giant planet Jupiter and was amazed to see three star-like objects close to the planet and a few nights later there were four. Night by night he observed these bodies and came to the startling conclusion that they were actually moons, orbiting the planet just as our moon orbited the Earth. Many critics of the Copernican Theory said that the Earth could not be moving through space or it would leave the Moon behind. Very clearly, Jupiter had some power that made its moons move with it so maybe the Earth had the same power over its own Moon. When Galileo tried to show the clerics these moons of Jupiter in his telescope some refused to look of the ones that tried some said that they could see nothing. He went on to discover the phases of Venus, sunspots and was the first to see the rings of Saturn although he had no idea just what they were. His astronomical discoveries were published in a short book, "The Starry Messenger" in 1610 and his observations of sunspots were published in 1612 in "Discourse on Floating Bodies". In December 1612 and January 1613 his sketches show another object close to Jupiter that moved against the background stars. This object was the planet Neptune but Galileo did not realize it and so it went undiscovered for the next 223 years.

The Cardinals of the Inquisition met on February 24th 1616 and condemned the teachings of Copernicus which had the Sun at the centre of the universe. These teachings were in direct conflict with the Catholic Church's philosophy of an Earth centered universe and Galileo was ordered to abandon the opinion that the Sun was the centre of the universe and he was not to hold, teach or defend it. He was made to kneel and promise to abandon the false opinion that the Sun was the centre of the universe and immovable, and to agree that it was indeed the Earth that was at the centre of universe and did not move. It is believed that as he rose to his feet he muttered the words "but still it moves".

Galileo decided to air his views in a publication which takes the form of a dialogue between two fictitious characters, Salviati and Simplico, in which one argued for the Ptolemaic system and the other argued for the Copernican system. Unfortunately Galileo made Simplico, who argued for the Earth centered universe, seem like a buffoon while Salviati appeared as an intellectual and presented the strongest arguments for the Sun centered universe. The publication, titled "Dialogue Concerning the Two Chief Systems of the World - Ptolemaic and Copernican", enraged the church and its sale was banned and Galileo was summoned to again appear before the Inquisition. Found guilty of heresy, he was condemned to life imprisonment which was lightened to house arrest rather than an actual prison sentence. While under house arrest Galileo devoted himself to physics and his final book, "Discourses and Mathematical Demonstrations Relating to Two New Sciences", dealt with the strength of materials and the way objects move. Albert Einstein regarded this book as one of the most important in the history of science. Galileo went completely blind in 1638 and died on January 8th 1642 Pope John Paul II gave an address on October 31st 1995 on behalf of the Catholic Church in which he admitted that errors had been made by theological advisors in the case of Galileo and in March 2008 the Vatican proposed to erect a statue of him inside the Vatican walls.

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