The Story of Astronomy

by Peter Aughton

  We must also give a mention to the astronomer Arzachel (1028–87), who lived in the Andalusian region of Spain. He was the foremost “Spanish-Arab” astronomer of his time. He carried out a series of observations at Toledo, and he presented his work in the Toledan Tables. He corrected geographical data from the time of Ptolemy, and in the 12th century his tables were translated into Latin. Arzachel was the first to prove conclusively that there was a small precession of the Earth’s orbit relative to the stars. He measured a precession of 12.04 seconds of arc per year—a brilliant and accurate piece of observation and remarkably close to the modern accepted value of 11.8 seconds. In a later chapter we shall look at the much smaller precession of the orbit of Mercury and its importance to astronomy. Arzachel invented a novel form of flat astrolabe, known as a safihah, details of which were published in Latin, Hebrew and several European languages. His work was well known to Copernicus who, in his De Revolutionibus Orbium Coelestium, quotes Arzachel and Albategnius and acknowledges his debt to their work.

  Omar Khayyam, Astronomer-poet

  We now come to the best-known and the most-honored of the Persian astronomers. He was the astronomer-poet Omar Khayyam, who lived from 1044–1122. The name khayyam means “tentmaker” in Arabic, and there is some evidence that his father was indeed a tentmaker and that he himself practiced this trade for a short time.

  A Persian nobleman called Nizam ul Mulk was educated at the same school as Omar Khayyam, in Nishapur, the provincial capital of Khurasan. Nizam described his first meeting with Omar Khayyam:

  When I first came there I found two other pupils of mine own age newly arrived, Hakim Omar Khayyam, and the ill fated Ben Sabbah. Both were endowed with sharpness of wit and the highest natural powers; and we three formed a close friendship together. When the Imam rose from his lectures, they used to join me, and we repeated to each other the lessons he had heard. Now Omar was a native of Nishapur, while Hasan Ben Sabbah’s father was one Ali, a man of austere life and practice, but heretical in his creed and doctrine.

  Omar Khayyam attended other institutions of learning, including those at Bukhara, Balkh, Samarkand and Isphahan, but he lived in Nishapur and Samarkand in Central Asia for most of his life. On the accession of Din Malik Shah (1055–92) as sultan of Jalal, Omar Khayyam was appointed court astronomer with an observatory in Esfahan. Other leading astronomers were brought to the court, and for about 18 years Omar Khayyam supervised his team of astronomers to produce work of very high quality. During this time Khayyam was responsible for compiling astronomical tables, and he contributed to a calendar reform in 1079. He calculated the length of the year as 365.24219858156 days—a grossly over-accurate figure quoted to a precision not even achievable today. It is correct as far as the fifth decimal place, but it is almost certainly built upon the work of Albategnius a century before him, who in turn had access to the work and observations of Ptolemy and the Alexandrian scholars.

  Omar Khayyam is one of the select group of astronomers who also made original contributions to the advance of mathematics. A good example is his work on algebra, which became known throughout Europe in the Middle Ages. His skill as a mathematician was legendary in his time. In his book on algebra he classified many algebraic equations based on their complexity. When he came to study the cubic equation he identified no less than 13 different forms. He went on to discover a geometrical method to solve cubic equations by finding the intersection of a parabola with a circle. He studied probability, including what we now call binomial probability, and he produced figures for what we know as Pascal’s triangle. He questioned whether or not a ratio should be regarded as a number. To put his work into perspective it must be said that the Romans also had the means to solve the cubic equation and they, too, used a geometric method, so Khayyam’s method was probably a derivation from an earlier method. It is also well known that in the third century BC the Alexandrian mathematician Apollonius wrote a treatise on the conic sections. This was also known to the Arabians, but very few could master the ancient texts and Omar Khayyam’s contribution is seen as a new development to an old problem. He extended Euclid’s work by giving a new definition of ratios and showed how to handle the multiplication of ratios. He also contributed to the theory of parallel lines.

  The Rubaiyat

  Omar Khayyam not only made original contributions to science but also to literature. In fact he is better known as a poet than as an astronomer, and he is certainly the best-known Arabian poet in the Christian world. His fame is due to the Englishman Edward Fitzgerald (1809–83) who translated into English the Rubaiyat of Omar Khayyam, a collection of 100 short, four-line poems, and then published them in 1859. The English version of the Rubaiyat has gone to several editions. This is in spite of the fact that a lot is lost by the translation into English. It has to be said that Edward Fitzgerald took a few liberties in his translation and to help with the marketing, and he wrote the first stanza entirely on his own!

  Wake, For the Sun, who scattered into flight

  The Stars before him from the field of night,

  Drives Night along with them from Heav’n, and strikes

  The Sultan’s Turret with a Shaft of Light.

  The Rubaiyat contains very little astronomy, and when it does it is only in support of the philosophy:

  LXXII

  And that inverted bowl they call the sky,

  Whereunder crawling cooped we live and die

  Lift not your hands to it for help—for it

  As impotently moves as you or I.

  His best-known quatrain came when he was pondering the past and the future of the universe. He decided that it was impossible to change the past. He was able to express his thoughts far better than most:

  LXXXI

  The moving finger writes; and, having writ,

  Moves on: nor all your piety and wit

  Shall lure it back to cancel half a line.

  Nor all your tears wash out a line of it.

  Earlier in the chapter we had a description of Omar Khayyam as a pupil by one of his contemporaries. We now have an account of the mature Omar Khayyam, the teacher, as described by one of his pupils, Khwajah Nizami of Samarkand, who relates the story:

  I often used to hold conversations with my teacher, Omar Khayyam, in a garden; and one day he said to me, “My tomb shall be in a spot where the north wind may scatter roses over it.” I wondered at the words he spake, but I knew that his were no idle words. Years after, when I chanced to revisit Nishapur, I went to his final resting place and lo! It was just outside a garden, and trees laden with fruit stretched their boughs over the garden wall, and dropped their flowers upon his tomb, so that the stone was hidden under them.

  Omar Khayyam’s ten books and 30 monographs have survived. These include books on mathematics, algebra, geometry, physics and metaphysics.

  The Fall of the Moors

  For centuries, the Spanish had been eager to expel the Moors from southern Spain. In the 11th century the fabled warrior El Cid (c.1040–99) fought to drive out the Moors. In this endeavor he had the backing of the pope, who wished to convert the Arabs to Christianity. El Cid was considered the perfect Christian knight: chivalrous, gentle and magnanimous in his conquests. But nothing could be further from the truth; he terrorized the Arabs with his night raids. He and his men raped innocent women, pillaged and plundered the houses and mosques and gave no quarter. In 1135 the Muslim city of Toledo fell to the Spanish. Rumors spread about new finds in Toledo, and inquisitive travelers came to see what they could plunder. It became obvious to the educated that a great center of culture and civilization existed there. It was also obvious to the unbiased observer that it was the Europeans, not the Moors, who were the barbarians in southern Spain.

  In England, not long after the Norman conquest, a monk called Adelard of Bath (c.1080–c.1152) heard a rumor that rare manuscripts had been discovered in a part of Spain. Copyists and translators from all over Europe were soon on their way to Spain to try to gai
n access to the knowledge. Adelard was lucky. He found his way to Toledo and there, to his joy and amazement, he discovered a wonderful library where he was able to procure rare documents for his own use. Others heard of Adelard’s success and followed him across the Pyrenees and into Spain.

  In 711 Muslim Arabs under the leadership of Tariq ibn Ziyad (died 720) crossed the Strait of Gibraltar from Tangier and invaded southern Spain, ending the Visi-gothic rule there. Henceforth Andalusia’s history was closely linked with that of Morocco and the North African coast until the end of the 15th century.

  It is fascinating to ask how long it took after the fall of Rome for knowledge to grow and surpass the point it had reached in the ancient world. Most historians would say that it was not until the Renaissance that mankind could claim to have gained knowledge that the ancients had not discovered. As regards astronomy, the setback was more than a thousand years. It was not until after the time of Copernicus (1473–1543) that knowledge of astronomy advanced beyond that of the ancient world.

  5

  THE COPERNICAN REVOLUTION

  In the 16th century the astronomer Nicolaus Copernicus shook the world with his heretical assertion that it was the Sun, not the Earth, that lay at the center of the universe. Such was the expected weight of opinion against this theory that Copernicus’ views were only published after his death.

  Ptolemy’s Almagest was translated into Arabic in the ninth century, but a Spanish version of his work did not appear until the 12th century. It was translated into Latin in the time of Frederick II of Denmark (reigned 1559–88) and thus became available to the majority of European scholars. In the early Middle Ages there was still much interest in astronomy, although there were few active observers. In the monasteries the primary task of the monks was to copy the gospels into Latin and other languages. They occasionally came across scientific manuscripts, however, and sometimes these were also copied. Toward the end of the first millennium we sometimes find chronicles of historical events. The Anglo-Saxon Chronicle is a good example: it contains copious references to astronomical events, and when an eclipse or a comet is mentioned it is usually possible to put an exact date to the sighting.

  Thus in the year 540: “The Sun darkened on June 20th, and the stars showed fully nearly an hour past nine in the morning.” In 678: “there appeared the star called a comet, in August; and it shone for three months each morning like a beam of the Sun.” The chronicle records that in 1066: “it happened that all through England such a sign as the heavens was seen as no man had seen before. Some men said it was the star ‘Comet,’ that some men called the long-haired star. It appeared first on the eve of Letania maior, April 24th, and so shone all seven nights.”

  Visions in the Sky

  The “long-haired star” was literally woven into the fabric of English history when it appeared prominently on the Bayeux Tapestry. Six hundred years later Edmond Halley identified the object as a comet that reappeared every 76 years. A new star appeared a few years before the comet. It was first seen on July 4, 1054, and it was so bright that for several months it was visible in broad daylight. Chinese astronomers recorded the event, but there is no mention of it in European records. Nine hundred years later it became identified with a remnant of a supernova (an exploding star) in the Crab Nebula, and for a time it became the most intriguing object in the whole of the night sky.

  Comets and exploding stars are rare events, but changes to the face of Moon are so uncommon that they are virtually unknown. One summer evening in 1178 five English monks were relaxing and staring at the night sky. There was a new Moon, and as they gazed at it they noticed something very strange. A great explosion appeared to be taking place on the Moon before their eyes. The monks knew that the face of the Moon never changed, and so they realized they had witnessed a very unusual event. They did not understand what had happened, but they felt that the event must be a message of some kind from the heavens. They decided to report their findings to a higher authority, and so they made their way to Canterbury where they gained an audience with the archbishop. They swore the truth of their story under oath, and we know a little about the event because it was recorded by the chronicler Gervase of Canterbury (c.1141–c.1210):

  There was a bright new Moon, and as usual in that phase its horns were tilted towards the east. Suddenly the upper horn split in two. From the mid point of the division, a flaming torch sprung up, spewing out fire, hot coals and sparks.

  The Moon is covered with craters—the result of being regularly struck by objects from space in its long history. It is probable that the monks actually witnessed a large object such as a meteorite striking the Moon. Recent research suggests that the crater named after Giordano Bruno may be the result of the impact witnessed in 1178. (The Earth has suffered similar attacks in the past, but over time the weather has worn all but the largest craters away so that they are far less obvious.)

  A Treatise on the Astrolabe

  The Middle Ages are dotted with astronomical observations, but there are no radical new ideas about the structure of the universe recorded in this period. Astrologers were common, but few could also be called astronomers. The anecdotes can still be of interest, however. Geoffrey Chaucer (c.1343–1400), better known as the founder of English literature, wrote a treatise on the astrolabe, the oldest astronomical instrument. Chaucer had a son, Lewis, who it seems was more interested in mastering numbers than following in his father’s footsteps and mastering words. Chaucer decided to write a treatise on the astrolabe for the benefit of his son. For one who did not have any formal education in mathematics and the sciences, Chaucer’s mastery of the instrument must be admired:

  Litel Lowis my sone, I have perceived wel by certeyne evidences thyn abilite to lerne sciencez touchinge noumbres and proporcions; and as well considere I thy bisy preyers in special to lerne the Tretis of the Astrolabie. Than, for as mechel as a philosophre seith, “he wrappeth him in his frend, that condesendeth to the rightful preyers of his frend,” ther-for have I given thee a suffisaunt Asrolabie as for oure orizonte, compowded after the latitude of Oxenford; op-on which, by mediacion of this litel treatis, I purpose to teche thee a certain nombre of conclusions apertening to the same instrument.

  A Long and Varied Education

  In Chaucer’s time, Britain was seen as backward and uncivilized compared with places like Italy and Spain. So when the first glimmerings of a scientific revolution appeared, it was in the cultured cities of Italy. However, it was in a most unlikely eastern European town that the astronomical knowledge of 13 centuries first came into question. Nicolaus Copernicus, the son of a well-to-do merchant, was born on February 19, 1473, in Torun, a city on the River Vistula in north-central Poland. Nicolaus was the youngest of four children. After his father’s death, around 1484, Nicolaus’ uncle, Lucas Watzenrode (1447–1512), took him and his three siblings under his protection. Watzenrode, who later became bishop of the Chapter of Warmia, provided for young Nicolaus’ education and helped him to make his future career as a church canon.

  For two years from 1491, Copernicus studied liberal arts, including a smattering of astrology, at the University of Cracow. He left the university before completing his degree, but in 1493 he resumed his studies in Italy at the University of Bologna. He stayed in Bologna for four years, studying law. For a while he lived in the same house as the principal astronomer at the university, Domenico Maria de Novara (1473–1543), who held the post of official astrologer for the city. It seems certain that Novara introduced Copernicus to Ptolemy’s work—not to the original writings but to one of the later versions containing certain corrections and critical expansions of the models of the planetary orbits. These corrections were of great interest to Copernicus, and they may have suggested to him the ideas that led toward formulating his famous heliocentric hypothesis.

  In 1501 we find Copernicus at Frombork in Poland, but soon he returned to Italy to continue his studies, this time at the University of Padua, where he had changed his
direction of study from law to medicine. Copernicus’ astrological experience at Bologna was actually a better training for medicine than we might imagine, for at that time there was so much faith in astrology that the stars were thought to influence parts of the body, and a good horoscope was considered a very valuable aid toward a diagnosis. In 1503 Copernicus received his doctorate, not in astrology or in medicine but in canon law, for he had changed his direction of study yet again.

  When he returned to Poland his uncle arranged a sinecure for him at Cracow. Copernicus’ duties were largely administrative and medical. He collected rents from church-owned lands; he secured military defenses; he oversaw chapter finances; he managed the bakery, brewery and the mills; and he cared for the medical needs of his uncle and the other canons. His astronomical work took second place to his other duties, but it occupied all of his spare time.

  Formulating a Heliocentric Hypothesis

  By 1514, at the age of 41, Copernicus was regarded as a competent astronomer. In that year he was invited to offer his opinion at the church’s Fifth Lateran Council on the problem of the reform of the calendar. The civil calendar then in use was the one produced 15 centuries earlier by Sosigenes under Julius Caesar. Over the centuries since it was instigated it had fallen about ten days out of alignment with the stars, and the church was concerned that it cast doubts over the true dates of crucial feast days—Easter in particular. It is unlikely that Copernicus ever offered any views on how to reform the calendar, however, because there is no record that he ever attended any of the council’s sessions. In time Copernicus went to live again at Frombork. He took up residence in a tower of the cathedral house, a high observatory from where he was free to continue his astronomical studies. His revolutionary ideas had probably been forming in his mind for many years, but it was at Frombork that we first learn about them.