Magnetite and Lodestone

Magnetite is one of the most common oxide minerals and also one of the most common iron minerals. It is an important ore of iron and is found in igneous, metamorphic and sedimentary rocks. It can also be abundant in sediments.

Identification of Magnetite

Magnetite is easy to identify. It is a black, opaque, submetallic to metallic mineral with a hardness between 5.5 and 6.5. It is often found in the form of isometric crystals. However, its magnetic properties are distinctive. It is one of just a few minerals that are attracted to a magnet. It is the most magnetic mineral found in nature. Sometimes it is automagnetized and attracts metal objects.

Magnetite as "Lodestone"

Lodestone is a form of magnetite that acts as a natural magnet. Normal magnetite is attracted to a magnet but lodestone acts as a magnet, attracting iron particles (see photo).

Use of Magnetite As An Ore of Iron

Most of the magnetite mined is used as an ore of iron. Iron liberated from the ore is usually used to make steel.

Use of Magnetite as a Heavy Media

Powdered magnetite is often mixed with a liquid for used as a heavy media for specific gravity separations. Much of the high sulfur coal that is mined is floated across a slurry of magnetite. Clean coal particles float and those contaminated with pyrite (a sulfur mineral) sink into the high-density slurry.

Use of Magnetite as an Abrasive

The abrasive known as "emery" is a natural mixture of magnetite and corundum. Some synthetic emery is produced by mixing magnetite with aluminum oxides. Producing it synthetically allows control over the particle size and the relative abundance of aluminum oxide and magnetite. Some finely ground magnetite is also used as an abrasive in water jet cutting.

Other Uses of Magnetite

Other uses include: as a toner in electrophotography, as a micronutrient in fertilizers, as a pigment in paints, as an aggregate in high-density concrete.

Magnetite and Earth's Magnetic Field

Tiny crystals of magnetite are present in many rocks. In the crystallization of an igneous rock, tiny crystals of magnetite form in the melt, and because they are magnetic, they orient themselves with the direction and polarity of Earth's magnetic field. This preserves in the rock the orientation of Earth's magnetic field at the time of crystallization.

Today geologists can study the magnetic properties of rocks of various age and reconstruct the history of change in Earth's magnetic field. This information is available for multiple locations on multiple continents. It can also be used to learn about the movement of continents over time.

A similar orientation of tiny magnetite grains occurs in the settling of sediment particles, locking clues to Earth's magnetic history into some sedimentary rocks.

Galileo Galilei

Galileo Galilei is justly known for many contributions to science, as well as for his persecution and confinement under the Inquisition. But among his most memorable achievements is his adaptation of a novel instrument, the telescope, with which he observed the Moon, discovered four satellites of Jupiter, resolved nebular patches into stars, and observed the phases of Venus. In the process, he helped lead a revolution in cosmology — along with his fellow astronomers — that conclusively toppled the traditional Aristotelian model in favor of the Copernican system.

Historians generally agree that the telescope originated in the Netherlands, with two simultaneous patent applications appearing in October 1608; a third inventor apparently developed a telescope around the same time and attempted to sell it at the Frankfurt Fair. These designs consisted of a convex and concave lense in a tube, able to magnify objects by two or three times their original size. The news of the invention spread rapidly throughout Europe, and samples of the device soon followed. By April 1609, citizens could purchase three-powered spyglasses in local spectacle makers' shops in Paris; within four months, they were also available in Italy.

News of this marvelous new instrument for "seeing faraway things as though nearby" reached Galileo in May 1609, and he quickly duplicated the invention and constructed his own three-powered telescope that summer, then set about making improvements in the design. He presented an eight-powered instrument to the Venetian Senate in August, and was rewarded with a doubling of his salary and lifetime tenure at the University of Padua. By late October, he had completed a twenty-powered telescope, which is when he first turned it to the heavens to observe celestial bodies.

Galileo initially used the instrument for a series of observations of the Moon, which neared completion at the end of 1609, when Jupiter was at opposition and closest to the Earth, and hence the brightest object in the evening sky, apart from the Moon itself. After making the necessary adjustments, he began observing the planet, noting on 7 January 1610 that Jupiter appeared to have three fixed stars nearby. Intrigued, he returned to the planet the following evening, expecting the then-retrograde planet to have moved from east to west, leaving the three little stars behind. Instead, Jupiter seemed to have moved to the east — an interesting anomaly.

Puzzled by the planet's behavior, Galileo returned to the formation repeatedly, observing several key details. First, the little stars never left Jupiter, but appeared to be carried along with the planet. Second, as they were carried along, they changed their position with respect to each other and to Jupiter. Finally, there were four of these little stars. By the 15th of January, he concluded the objects were not fixed stars, but planetary bodies that revolved around Jupiter. The planet had four moons-strong support for Copernican theory. He published this groundbreaking observation in his book, Sidereus Nuncius, which appeared in Venice in the middle of March 1610, guaranteeing his fame and ensuring his place in scientific history.

Following the publication of the Sidereus Nuncius, Galileo continued to make observations of celestial objects. In July 1610, he first remarked on the strange appearances of Saturn, which sometimes seemed to be oval, sometimes two lateral bodies, and at other times solitary and perfectly spherical-another puzzling enigma. By December, he was able to verify the observations of other astronomers that Venus has phases similar to the Moon, providing additional proof that Venus orbits the Sun, in conformance with the Copernican System.

The product of craftsmen, rather than an invention of scientists, the telescope nonetheless enjoys an important place in history as the prototype of modern scientific instruments. The observations made by Galileo and his scientific colleagues revealed hitherto unsuspected phenomena in the heavens and had a profound impact on the 17th century controversy between followers of the traditional geocentric astronomy and those who favored the heliocentric system of Copernicus.

Johannes Kepler

Johannes Kepler (December 27, 1571 – November 15, 1630), a key figure in the scientific revolution, was a German mathematician, astronomer, astrologer, and an early writer of science fiction stories. He is best known for his laws of planetary motion, based on his works Astronomia nova, Harmonice Mundi and the textbook Epitome of Copernican Astronomy.

Through his career Kepler was a mathematics teacher at a Graz seminary school (later the University of Graz), an assistant to Tycho Brahe, court mathematician to Emperor Rudolf II, mathematics teacher in Linz, and court astrologer to General Wallenstein. He also did fundamental work in the field of optics and helped to legitimize the telescopic discoveries of his contemporary Galileo Galilei.

He is sometimes referred to as "the first theoretical astrophysicist", although Carl Sagan also referred to him as the last scientific astrologer.

Life

Childhood and education (1571–1594)

Kepler was born on December 27, 1571 at the Imperial Free City of Weil der Stadt (now part of the Stuttgart Region in the German state of Baden-Württemberg, 30 km west of Stuttgart's center). His grandfather had been Lord Mayor of that town, but by the time Johannes was born, the Kepler family fortunes were in decline. His father earned a precarious living as a mercenary, and he left the family when Johannes was five years old. He was believed to have died in the war in the Netherlands. His mother, an inn-keeper's daughter, was a healer and herbalist who was later tried for witchcraft. Born prematurely, Johannes claimed to have been a weak and sickly child. Despite his ill health, he was precociously brilliant. As a child, he often impressed travelers at his grandfather's inn with his phenomenal mathematical faculty.

He was introduced to astronomy/astrology at an early age, and he developed a love for it that would span his entire life. At age five, he observed the Comet of 1577, writing that he "was taken by [his] mother to a high place to look at it." At age nine, he observed another astronomical event, the Lunar eclipse of 1580, recording that he remembered being "called outdoors" to see it and that the moon "appeared quite red". However, childhood smallpox left him with weak vision, limiting him to the mathematical rather than observational aspects of astronomy.

In 1589, after moving through grammar school, Latin school, and lower and higher seminary in the Lutheran education system, Kepler began attending the University of Tübingen as a theology student, where he proved himself to be a superb mathematician and earned a reputation as a skillful astrologer. Under the instruction of Michael Maestlin, he learned both the Ptolemaic system and the Copernican system; he became a Copernican at that time, defending heliocentrism from both a theoretical and theological perspective in student debates. Despite his desire to become a minister, near the end of his studies, Kepler was recommended for a position as teacher of mathematics and astronomy at the Protestant school in Graz, Austria. He accepted the position in April 1594, at the age of 23.

Early career (1594–1601)

In Graz, Kepler began developing an original theory of cosmology based on the Copernican system, which was published in 1596 as Mysterium Cosmographicum—The Sacred Mystery of the Cosmos.

In April 1597, Kepler married Barbara Müller. She died in 1611 and was outlived by two of Johannes's children and one by an earlier marriage.

In December 1599, Tycho Brahe wrote to Kepler, inviting Kepler to assist him at Benátky nad Jizerou outside Prague. Pressured to leave Graz by increasingly strict Counter-Reformation policies restricting the religious practices and political rights of Protestants, Kepler joined Tycho in 1600. After Tycho's death in 1601, Kepler was appointed Imperial Mathematician in his place, a post he would retain through the reigns of three Habsburg Emperors (from November 1601 to 1630).

Imperial Mathematician in Prague (1601–1612)

As Imperial Mathematician, Kepler inherited Tycho's responsibility for the Emperor's horoscopes as well as the commission to produce the Rudolphine Tables. Working with Tycho's extensive collection of highly accurate observational data, Kepler also set out to refine his earlier theories but was forced to abandon them. Instead, he began developing the first astronomical system to use non-circular orbits; it was completed in 1606 and published in 1609 as Astronomia Nova—New Astronomy. Astronomia Nova contained what would become the first and second laws of planetary motion.

In October 1604, Kepler observed the supernova which was subsequently named Kepler's Star (a term which may also refer to the stellated octahedron). In 1611, Kepler published (as a letter to a friend) a monograph on the origins of snowflakes, the first known work on the subject. He correctly theorized that their hexagonal nature was due to cold, but did not ascertain a physical cause for this. In January 1612, the Emperor died. To escape the growing religious tension in Prague, Kepler took the post of Provincial Mathematician in Linz.

Teaching in Linz and final years (1612–1630)

In 1615, Kepler married Susanna Ruettinger, with whom he would have several children.

In 1617, Kepler's mother Katharina was accused of being a witch in Leonberg. Beginning in August 1620 she was imprisoned for fourteen months. Thanks in part to the extensive legal defense drawn up by Kepler, she was released in October 1621 after failed attempts to convict her. However, she was subjected to territio verbalis, a graphic description of the torture awaiting her as a witch, in a final attempt to make her confess. Throughout the trial, Kepler postponed his other work (on the Rudolphine Tables and a multi-volume astronomy textbook) to focus on his "harmonic theory". The result, published in 1619 as Harmonices Mundi ("Harmony of the Worlds") contained the third law of planetary motion.

Kepler completed the last of seven volumes of his textbook Epitome of Copernican Astronomy in 1621, which brought together and extended his previous work and would become very influential in the acceptance of the Copernican system over the next century. In 1627 he completed the Rudolphine Tables, which provided accurately calculated future positions of the planets and allowed the prediction of rare astronomical events.

On November 15, 1630 Kepler died of a fever in Regensburg. In 1632, only two years after his death, his grave was demolished by the Swedish army in the Thirty Years' War.

Work

Kepler lived in an era when there was no clear distinction between astronomy and astrology, while there was a strong division between astronomy/astrology (a branch of mathematics within the liberal arts) and physics (a branch of the more prestigious discipline of philosophy). He also incorporated religious arguments and reasoning into his work, such that the basis for many of his most important contributions was essentially theological (Barker & Goldstein, 2001).

Kepler was a Pythagorean mystic. He considered mathematical relationships to be at the base of all nature, and all creation to be an integrated whole. This was in contrast to the Platonic and Aristotelian notion that the Earth was fundamentally different from the rest of the universe, being composed of different substances and with different natural laws applying. In his attempt to discover universal laws, Kepler applied terrestrial physics to celestial bodies; famously, his effort produced the three Laws of Planetary Motion. Kepler was also convinced that celestial bodies influence terrestrial events. One result of this belief was his correct assessment of the moon's role in generating the tides, years before Galileo's incorrect formulation. Another was his belief that someday it would be possible to develop a "scientific astrology", despite his general disdain for most of the astrology of his time.

Scientific work

Kepler's laws

Main article: Kepler's laws of planetary motion

Kepler inherited from Tycho Brahe a wealth of the most accurate raw data ever collected on the positions of the planets. The difficulty was to make sense of it. The orbital motions of the other planets are viewed from the vantage point of the Earth, which is itself orbiting the sun. As shown in the example below, this can cause the other planets to appear to move in strange loops. Kepler concentrated on trying to understand the orbit of Mars, but he had to know the orbit of the Earth accurately first. In order to do this, he needed a surveyor's baseline. In a stroke of pure genius, he used Mars and the Sun as his baseline, since without knowing the actual orbit of Mars, he knew that it would be in the same place in its orbit at times separated by its orbital period. Thus the orbital positions of the Earth could be computed, and from them the orbit of Mars. He was able to deduce his planetary laws without knowing the exact distances of the planets from the sun, since his geometrical analysis needed only the ratios of their solar distances.

Unlike Brahe, Kepler held to the heliocentric model of the solar system. Starting from that framework, Kepler made twenty years of painstaking trial-and-error attempts at making some sense out of the data. He finally arrived at his three laws of planetary motion:

1. Kepler's elliptical orbit law: The planets orbit the sun in elliptical orbits with the sun at one focus.
   
2. Kepler's equal-area law: The line connecting a planet to the sun sweeps out equal areas in equal amounts of time.
   
3. Kepler's law of periods: The time required for a planet to orbit the sun, called its period, is proportional to the long axis of the ellipse raised to the 3/2 power. The constant of proportionality is the same for all the planets.
   

Using these laws, he was the first astronomer to successfully predict a transit of Venus (for the year 1631). Kepler's laws were the first clear evidence in favor of the heliocentric model of the solar system, because they only came out to be so simple under the heliocentric assumption. Kepler, however, never discovered the deeper reasons for the laws, despite many years of what would now be considered non-scientific mystical speculation. Isaac Newton eventually showed that the laws were a consequence of his laws of motion and law of universal gravitation. (From the modern vantage point, the equal-area law is more easily understood as arising from conservation of angular momentum.)

Kepler first discovered his distance-cubed-over-time-squared (or 'third') law of planetary motion on March 8, 1618 but rejected the idea until May 15, 1618, when he verified his result. This result was published in his Harmonices Mundi (1619).

On October 17, 1604, Kepler observed that an exceptionally bright star had suddenly appeared in the constellation Ophiuchus. (It was first observed by several others on October 9.) The appearance of the star, which Kepler described in his book De Stella nova in pede Serpentarii ("On the New Star in Ophiuchus's Foot"), provided further evidence that the cosmos were not changeless; this was to influence Galileo Galileo in his argument. It has since been determined that the star was a supernova, the second in a generation, later called Kepler's Star or Supernova 1604. No further supernovae have been observed in the Milky Way, though others outside our galaxy have been seen.

Other scientific and mathematical work

Kepler also made fundamental investigations into combinatorics, geometrical optimization, and natural phenomena such as snowflakes, always with an emphasis on form and design. He was also one of the founders of modern optics, defining for example antiprisms and the Kepler telescope (see Kepler's books Astronomiae Pars Optica—i.a. theoretical explanation of the camera obscura—and Dioptrice). In addition, since he was the first to recognize the non-convex regular solids (such as the stellated dodecahedra), they are named Kepler solids in his honor.

Kepler also was in contact with Wilhelm Schickard, inventor of the first automatic calculator, whose letters to Kepler show how to use the machine for calculating astronomical tables.

Mysticism and astrology

Kepler's Platonic solid model of the Solar system from Mysterium Cosmographicum (1596), Closeup of inner section of the model

Mysticism

Kepler discovered the laws of planetary motion while trying to achieve the Pythagorean purpose of finding the harmony of the celestial spheres. In his cosmologic vision, it was not a coincidence that the number of perfect polyhedra was one less than the number of known planets. Having embraced the Copernican system, he set out to prove that the distances from the planets to the sun were given by spheres inside perfect polyhedra, all of which were nested inside each other. The smallest orbit, that of Mercury, was the innermost sphere. He thereby identified the five Platonic solids with the five intervals between the six known planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn) and the five classical elements.

In 1596 Kepler published Mysterium Cosmographicum, or The Sacred Mystery of the Cosmos. Here is a selection explaining the relation between the planets and the Platonic solids:

Before the universe was created, there were no numbers except the Trinity, which is God himself… For, the line and the plane imply no numbers: here infinitude itself reigns. Let us consider, therefore, the solids. We must first eliminate the irregular solids, because we are only concerned with orderly creation. There remain six bodies, the sphere and the five regular polyhedra. To the sphere corresponds the heaven. On the other hand, the dynamic world is represented by the flat-faces solids. Of these there are five: when viewed as boundaries, however, these five determine six distinct things: hence the six planets that revolve about the sun. This is also the reason why there are but six planets…

I have further shown that the regular solids fall into two groups: three in one, and two in the other. To the larger group belongs, first of all, the Cube, then the Pyramid, and finally the Dodecahedron. To the second group belongs, first, the Octahedron, and second, the Icosahedron. That is why the most important portion of the universe, the Earth—where God's image is reflected in man—separates the two groups. For, as I have proved next, the solids of the first group must lie beyond the earth's orbit, and those of the second group within… Thus I was led to assign the Cube to Saturn, the Tetrahedron to Jupiter, the Dodecahedron to Mars, the Icosahedron to Venus, and the Octahedron to Mercury…

To emphasize his theory, Kepler envisaged an impressive model of the universe which shows a cube, inside a sphere, with a tetrahedron inscribed in it; another sphere inside it with a dodecahedron inscribed; a sphere with an icosahedron inscribed inside; and finally a sphere with an octahedron inscribed. Each of these celestial spheres had a planet embedded within them, and thus defined the planet's orbit.

In his 1619 book, Harmonice Mundi or Harmony of the Worlds, as well as the aforementioned Mysterium Cosmographicum, he also made an association between the Platonic solids with the classical conception of the elements: the tetrahedron was the form of fire, the octahedron was that of air, the cube was earth, the icosahedron was water, and the dodecahedron was the cosmos as a whole or ether. There is some evidence this association was of ancient origin, as Plato tells of one Timaeus of Locri who thought of the Universe as being enveloped by a gigantic dodecahedron while the other four solids represent the "elements" of fire, air, earth, and water. To his disappointment, Kepler's attempts to fix the orbits of the planets within a set of polyhedrons never worked out, but it is a testimony to his integrity as a scientist that when the evidence mounted against the cherished theory he worked so hard to prove, he abandoned it.

His most significant achievements came from the realization that the planets moved in elliptical, not circular, orbits. This realization was a direct consequence of his failed attempt to fit the planetary orbits within polyhedra. Kepler's willingness to abandon his most cherished theory in the face of precise observational evidence also indicates that he had a very modern attitude to scientific research. Kepler also made great steps in trying to describe the motion of the planets by appealing to a force which resembled magnetism, which he believed emanated from the sun. Although he did not discover gravity, he seems to have attempted to invoke the first empirical example of a universal law to explain the behaviour of both earthly and heavenly bodies.

Astrology

Kepler disdained astrologers who pandered to the tastes of the common man without knowledge of the abstract and general rules, but he saw compiling prognostications as a justified means of supplementing his meager income. Yet, it would be a mistake to take Kepler's astrological interests as merely pecuniary. As one historian, John North, put it, "had he not been an astrologer he would very probably have failed to produce his planetary astronomy in the form we have it." However, Kepler's views on astrology were quite unconventional for his time; he argued for a system of astrology based largely on harmonics, a type of 'planetary harmonics' based almost entirely upon the astrological aspects and what has been traditionally been termed "the music of the spheres." Information relating to his theories can be found in his book Harmonice Mundi.

Kepler believed in astrology in the sense that he was convinced that astrological aspects physically and really affected humans as well as the weather on Earth. He strove to unravel how and why that was the case and tried to put astrology on a surer footing, which resulted in the On the more certain foundations of astrology (1601), in which, among other technical innovations, he was the first to propose the quincunx aspect. In The Intervening Third Man, or a warning to theologians, physicians and philosophers (1610), posing as a third man between the two extreme positions for and against astrology, Kepler advocated that a definite relationship between heavenly phenomena and earthly events could be established.

At least 800 horoscopes and natal charts drawn up by Kepler are still extant, several of himself and his family, accompanied by some unflattering remarks. As part of his duties as district mathematician to Graz, Kepler issued a prognostication for 1595 in which he forecast a peasant uprising, Turkish invasion and bitter cold, all of which happened and brought him renown. Kepler is known to have compiled prognostications for 1595 to 1606, and from 1617 to 1624. As court mathematician, Kepler explained to Rudolf II the horoscopes of the Emperor Augustus and Muhammad, and Kepler gave astrological prognosis for the outcome of a war between the Republic of Venice and Paul V. In the On the new star (1606) Kepler explicated the meaning of the new star of 1604 as the conversion of America, downfall of Islam and return of Christ. The De cometis libelli tres (1619) is also replete with astrological predictions.

Johannes Kepler Stamps

Kepler on God

"I was merely thinking God's thoughts after him. Since we astronomers are priests of the highest God in regard to the book of nature," wrote Kepler, "it benefits us to be thoughtful, not of the glory of our minds, but rather, above all else, of the glory of God."

http://redalyc.uaemex.mx/redalyc/html/328/32849303/32849303.html

Nicolaus Copernicus (1473–1543)

Nicolaus Copernicus was a mathematician and astronomer who proposed that the sun was stationary in the center of the universe and the earth revolved around it. He was born on February 19, 1473, in Torun city of Poland in Europe. His was the son of Copernide and Barbara. Nicolaus was the youngest among two sons and two daughters. Torun was a big and prosperous trade centre at the time of the birth of this great scientist. His father was a scholarly magistrate of the city. Besides, he was a rich, cultured, distinguished social worker and a well-wisher of society. When Nicolaus was 10 years old, his father died. The children were then put under the care of their uncle Lucas. His uncle was a priest and educationist. He was a respected figure in society. It was but natural for the children to be brought in a cultured and religious environment. Young Nicolaus had made up his mind to become a preacher and accordingly focused his energies in this direction.

At the age of 18, Copernicus joined the Cracow University in Poland’s capital Cracow. It was a well-known institute at that time with some of the best teachers in the land. A highly reputed institute, it attracted intelligent students from as far as Germany, Hungary, Italy, and Switzerland who came here to study. Latin was prominent and important medium of instruction. To have a better understanding of literature, science and other subjects, it was essential to know Latin. After joining the university, Copernicus too gained proficiency in Latin. He then started taking deep interest in astronomy, geometry (mathematics) and geography besides other important areas of study then. It was a time when Columbus was successful in discovering the new continent of America. Copernicus was 10 Years old then. With time, sea voyages were on the rise and with bigger ships and increasing sea travel, more emphasis was laid on astronomy. The need for accurate almanacs was felt, for festivals were celebrated according to the dictates of the church. Such was the state of society during that period.

Copernicus education took a different turn. In 1496, after leaving Cracow University, he joined Bologna School of law in Itlay. From here he moved to the famous Padua University where he studied medicine during 1501-1505. Thereafter, he took his Doctor of Canon Law degree from Ferara Univesity and he arrived at his uncle’s place in Poland. Discussions and deliberations with his uncle who was a priest led to the conclusion that his doctorate would be useful in taking up religious work. It was believed then that medicine and astrology were closely related. Once again Nicolaus went to Padua University and joined the School of Medicine.

The famous astronomer and mathematician-scientist Ptolemy (90 AD to 168 AD) was born in Alexandria, Egypt. In the second century it was a big port city, besides being the cultural capital. To enhance their knowledge, intellectuals and thinkers from the country and abroad visited its well-stacked libraries and imposing museums in this city. Greek scholar Ptolemy, too visited this city many a time for his study. In 150 AD, Ptolemy had made some important observations regarding the motion of celestial bodies. Though he did not entirely understand many peculiarities of these heavenly bodies, he believed in what he saw and accepted the prevailing belief that the earth is stationery and the entire universe revolves around it. Therefore, he believed in the seeming truth that the Sun rises in the East and sets in the West.

Four centuries before Ptolemy, another Greek philosopher and astrologer had come to conclusion that the Sun was centre of the universe, but puritans did not heed to his conclusions and he was criticized. Ptolemy was influenced by popular belief. Accepting the geocentric (having the earth as centre) theory of the universe, Ptolemy based his calculations on it in his volume ‘The Great Treatise of Astronomy’, better known as ‘Almegaste’. Hence certain flaws appear in his calculations.

In Greek, ‘Planet means’ something that wanders on its own’. It had become an acceptable fact with philosophers, religious teachers and scientists, propagating the belief that the earth was stationary and the sun and other planets revolved around the earth. Ptolemy, the great scholar tried to explain the planetary motions and their positions, of which only some were true. Regarding the wrong calculations he had made, he justified them by calling them wandering celestial bodies. Poland’s famous scientist Copernicus was able to understand the complex planetary motions of these celestial bodies, but for this he had assumed that the Sun was at the centre of the universe.

It was by now clear that Sun and other planets revolved in orbits. During one such revolution, a celestial body in radial motion moves 360 degree. This circle is divided into 12 parts each of 30 degree. These are known as the Zodiac signs. Today we know that the Sun moves from one Zodiac sign to another, every month. Thus, in one year, the earth completes one revolution around the Sun. It was also believed then that there was an unknown link between the planets, Zodiac signs and the various organs of the body. On this basis and taking into account the birth time, astrologers draw the life chart of a person. Today too, people pay a lot of money to astrologers to know their future. In ancient India, Aryabhatt, Varahmihir, Brahmgupt, Bhaskaracharya and other astronomers were popular as astrologers.

During his learning years, Copernicus got a job as a junior priest in a church. Thus he received knowledge of science, religion and philosophy. Besides, he had studied law, which gave him a deep insight into the laws governing the church. Add to this his knowledge of Greek and Latin, and he was a well-versed scholar at the age of 33. He returned to Poland to serve his ailing uncle. Here his leisure hours were spent in independent study. This gave him a new insight into the universe and a scientific approach also. Initially, he accepted the ancient Greek and Arab calculations as they were. He had no appropriate instruments, but his was a thinking mind that worked wonders. On the basis of mathematics and philosophy he visualized the universe as a divine arrangement and made some observations. But all these remained in his notebooks.

This is precisely what took him to the peak of his popularity. In 1539, a 25-year-old German student named Georg Rheticus came to him. This bright young man impressed Copernicus. At 28, he joined Wittenberg University as professor. For two years Rheticus made a deep study of Copernicus’ notes and calculations. He came to the conclusion that Copernicus’ observations were very noteworthy and needed to be published. Taking into account the motions of planets Copernicus had classified them. He had clearly stated that the Sun is at the centre of the universe and all planets including the earth revolve around it. He had developed a theory based on it. Taking all these theories into account along with his theories, he wrote a treatise. But fearing a religious backlash due to Ptolemy’s widespread influence at that time, he did not get it published.

In 1543, with Copernicus falling ill, Georg Rheticus and his other friends took his permission to get his treatise printed and took it to Germany. The book was named De revolutionibus orbium coelestium (The revolution of the heavenly spheres). The credit for getting Copernicus’ notes printed in book form goes to Rheticus to an extent. When the printed book reached Copernicus, he was on his deathbed. He was in no condition to pass judgement or appreciate it. His heart had gone weak and his brain almost dead. He died on 24 May 1543.

Many rank this book along with Newton’s Principia. It sowed the seeds for discarding Ptolemy’s famous theory. Old and superstitions beliefs were given a burial and the path to the development of modern astronomy was thus laid. Fourteen centuries after Ptolemy had propounded his geocentric theory, Copernicus had presented his helio-centric theory. The stamp of religion was paramount at that time and no one dared oppose it. With Copernicus theory it was the dawn of a new era.

Tycho Brahe and the Armillary Sphere

Tycho Brahe's reputation as the pre-eminent observational astronomer of the sixteenth-century derives from his construction and use of a range of astronomical instruments of large size and remarkable accuracy. Tycho's own descriptions of these objects are to be found scattered throughout his publications and correspondence, but the most detailed accounts are to be found in the Astronomiae instauratae mechanica (1598). This work reveals that Tycho developed and utilised four types of observing armillary.

Initially Tycho designed a zodiacal armillary sphere, which could be used to obtain the ecliptic co-ordinates of celestial bodies (celestial longitude and latitude) directly, without any calculation. (His other observing instruments gave positions in horizontal co-ordinates). Tycho described the instrument as an improvement on the armillary spheres of Hipparchus and Ptolemy, because it utilised only four rings, rather than five or six. But he found that the accuracy of the instrument was compromised by distortions in the rings. One zodiacal armillary was remounted in equatorial form (see below) by 1581; however a passage in the Epistolae astronomicae (1596) implies that two of these instruments existed as late as 1591, although one had fallen out of use, so he must have constructed two or three. The equatorial armillary spheres were constructed to overcome the problem of the rings flexing or shifting under their own weight, and could be used to obtain the positions of stars in equatorial co-ordinates. Tycho had at least two of these instruments, which were composed of three or four rings. Subsequently, Tycho constructed a device he called "The Great Equatorial Armillary Instrument, Comprising One and a Half Circles." The one circle of this instrument was about 2.6 m in diameter, and was mounted on a self-centering axis. A fourth armillary instrument, also consisting of just one-and-a-half complete rings, was briefly described by Tycho as a portable instrument which could be used for observations in any co-ordinate system. All of these instruments were engraved using Tycho's transversal method, which allowed scales to be very finely subdivided , and were equipped with the sights he developed to eliminate parallax errors.

Tycho was the last astronomer in the Latin West to make extensive use of armillary spheres for the purpose of observation. However, his Astronomiae instauratae mechanica exerted a strong influence on the Jesuit astronomer and missionary Ferdinand Verbiest (1623-1688), and as a consequence the Imperial Observatory in Peking was equipped with armillary spheres and other instruments based on Tycho's designs in the 1670s.

Recommended Reading

A. Chapman, "Tycho Brahe in China: The Jesuit Mission to Peking and the Iconography of the European Instrument-Making Process", Annals of Science 41 (1984), pp. 417-433

A. Chapman, "Tycho Brahe: Instrument Designer, Observer, and Mechanician", Journal of the British Astronomical Association 99 (1989), 2, pp. 70-77

J. Dreyer, Tycho Brahe: A Picture of Scientific Life and Work in the Sixteenth Century, Edinburgh 1890. Reprinted New York 1963

H. Raeder, E. Strömgren, & B. Strömgren, Tycho Brahe's Description of His Instruments and Scientific Work, Copenhagen 1946

V. Thoren, The Lord of Uraniborg: A Biography of Tycho Brahe, Cambridge 1990