Showing posts with label Astronomy. Show all posts
Showing posts with label Astronomy. Show all posts

Sunday, September 4, 2022

Armillary Spheres

The "wooden terrestrial spheres" mentioned here are what we now call "armillary spheres." An armillary is a spherical arrangement of rings designed to mimic the orbits of the sun and planets around the Earth—or around the Sun, depending on the prevailing theory at the time. If the Earth is the center, it is a Ptolemaic sphere; if the Sun is at the center, it is a Copernican sphere. China and Greece each invented them BCE. Hipparchus credited Eratosthenes (276 - 194BCE) as the inventor.

An early Christian philosopher, John Philoponus, wrote the earliest extant treatise on the armillary sphere and the astrolabe. The oldest example of one we have today dates to the 11th century.

Gerbert d'Aurillac (946 - 1003), who became Pope Sylvester II in 999, had brought the armillary sphere to Western Europe. He was also responsible for introducing Western Europe to the abacus, the Hindu-Arabic numeral system we use today, and (possibly) the mechanical clock.

Sylvester used the armillary sphere and sighting tubes to determine the definitive position of the pole star and to record measurements for the tropics and the equator. His work was improved upon in the Renaissance by Tycho Brahe (1546 - 1601). Public figures would have an armillary sphere incorporated into their portraits to indicate their wisdom and knowledge.

I've written about clocks before, but I don't recall learning that Gerbert d'Aurillac invented it. I want to check that out; I'll let you know what I find.

Monday, February 21, 2022

Al-Kindi

Abu Yūsuf Yaʻqūb ibn ʼIsḥāq aṣ-Ṣabbāḥ al-Kindī (801-873CE) is called the Father of Arab philosophy. Born in Kufa and educated in Baghdad, he was instrumental in the translation of many Greek scholarly texts into Arabic. (Remember that a lot of classical scholarly knowledge came to Western Europe via Arabic translations.) He is also credited with introducing Indian numerals (what we mistakenly think of as Arabic numerals) into the Arab and western world.

He was a polymath who contributed to many fields, although he did not always find the scientific truth.

In astronomy he followed Ptolemy's geocentric theory of the solar system, and he was certain the planets followed circular orbits in obedience to God.

He was a chemist who debunked the idea of alchemy turning base metals into gold or silver. He was the first to distill pure ethanol, with which he created several perfumes. He also created cosmetics and pharmaceuticals, and wrote a book on the chemistry of perfume.

A recently discovered book of his in Istanbul, entitled (in English) A Manuscript on Deciphering Cryptographic Messages shows that he was a pioneer in cryptography with the first known explanation of how to decipher encrypted messages by analyzing the frequency of letters.

He wrote on pollution, environmentalism, and meteorology, and explained tides as a result of heating and cooling.

He published 15 treatise on music theory—five of which have survived—including the first known written use of the term "music" (musiqia); he urged the use of music in therapy.

In optics, he explained that both the eye and the object seen must be linked by a transparent medium (air) filled with light. He criticizes Anthemius of Trailes for reporting that sunlight could be focused in war to cause opposing warships to burst into flame. Anthemius did not witness it himself. Al-Kindi performed experiments to be certain this would actually work.

His theory that time, space, motion, and bodies were not absolutes but relative to other objects and the observer puts him closer to Einstein than to Galileo and Newton.

Although his belief that philosophy could support theology was contested by many Arabic scholars who followed him, his writings laid the groundwork much of Arabic philosophy to come.

He also applied mathematics to pharmacology, which I'll talk about tomorrow.

Monday, November 30, 2015

Medieval Eclipses

[source]
Eclipses were a mystery for awhile, but eventually enough took place that astronomers could spot the patterns. European astronomers in the 1600s were able to publish books explaining how lunar and solar eclipses took place. Prior to that, however, they were mysterious occurrences whose importance was tied to whatever was happening on the ground.

In 632, an eclipse that was visible in Medina on 27 January coincided with the death of Ibrahim, the son of the Prophet Muhammad. Muhammad interpreted this as a sign for his followers to pray for Ibrahim.

On 2 August 1133, a total eclipse took place. When King Henry I of England died months later, it "confirmed" for the popular culture that eclipses were bad omens for rulers. They knew that the eclipse portended bad news; they just had to wait a long time to find out what the bad news was.

There's a stone in Ireland whose carvings are interpreted as the first recorded eclipse. You can see it above. The two sets of concentric circles colliding in the middle represent the eclipse. The circular carvings above it represent the other stars that appeared in the sky at the moment of totality. The overall pattern enabled astronomers to determine when the eclipse took place. So it is pretty well established that the earliest recording of an eclipse was made on the Loughcrew Cairn Megalithic Monument in Ireland; the eclipse took place on 30 November, 3340 BCE.

Monday, October 27, 2014

A Sultan's Observatory

The Ulugh Beg Observatory Museum, built in 1970
Ulugh Beg is the more familiar name of Mīrzā Muhammad Tāraghay bin Shāhrukh (22 March 1394 - 27 October 1449). "Ulugh Beg" is more of a nickname, meaning "Great Ruler."

He was a grandson of Tamerlane who became sultan in Samarkand while still a teenager. He decided to turn Samarkand into an intellectual center, building a university and inviting scholars to take up residence.

He also built the Ulugh Beg Observatory in 1420, where some of the finest Islamic astronomers worked and studied, but only those whom Ulugh personally approved. The picture here is a modern structure on the site of the original, which was destroyed by religious fanatics in 1449. An excavation uncovered its primary feature—a giant sextant:
The so-called "sextant" obviously would have extended well above the ground (as the drawing shows) and likely was closer to being a quadrant. As Krisciunas points out in his interesting discussion of the instrument, it "was by far the largest meridian instrument ever built." Fragments of the curved measuring track have survived with markings for around 20 degrees; this is about the highest point that observations likely would have been made. The "sextant" would have been used to measure the angle of elevation of major heavenly bodies, especially at the time of the winter and summer solstices. Light
from the given body, passing through a controlled opening, would have shone on the curved track, which is marked very precisely with degrees and minutes. "It could achieve a resolution of several seconds of arc--on the order of a six-hundredth of a degree, or the diameter of an American penny at a distance of more than half a kilometer" (Krisciunas). It is not clear whether more than the sun and moon could have been measured in this fashion, since planets, for example, would not have cast sufficient light. [link]
Building a giant permanent astronomical instrument was a unique idea at the time—remember that this was 200 years prior to the invention of a telescope. He created a catalog of over 1018 stars, discovering and correcting many inaccuracies in the star tables created by Ptolemy. Copies of these star charts are on display at the Ulugh Beg Observatory Museum; the originals are in the Bodleian Library in Oxford.

Wednesday, August 6, 2014

St. Dominic

The Dominicans have been mentioned many times, and their founder has been mentioned as a friend of Simon de Montfort, but his life deserves a little more attention.

St. Dominic is most often referred to (prior to canonization, that is) as Dominic Guzmán. He was born in 1170 in Castile, and was supposedly named for an earlier St. Dominic.* Nothing reliable is known of his family, since the earliest chroniclers had no interest in his parents and later chroniclers naturally tried to make his parentage sound impressive.**

In 1191, when Spain was suffering from famine, the young university student Dominic sold all he owned—including his clothes—for money to feed the starving poor. A few years later he joined the Canons Regular, who followed the rule of St. Augustine.

In 1215, the year of the Fourth Lateran Council (mentioned here and other places), Dominic and six disciples started their own house in Toulouse with some monastic rules, and were given permission by the local bishop to preach in Toulouse. That same year, Dominic and the bishop went to Rome to request permission for the founding of a new order to combat heresy; it was given by Pope Honorius III in the winter of 1216/17 and called Ordo Prædicatorum ["Order of Preachers"] (which is why, although referred to as "Dominicans," they have the initials "OP" after their names).

Interest in his order grew, and although his headquarters was in Rome where the pope had given the Dominicans a house, Dominic constantly traveled to keep in touch with the various chapters. We are told that he abstained from meat and excessive food and talking, and that he never allowed himself to sleep in a bed. The use of the rosary is attributed to him: it was known earlier, but he certainly promoted it as a guide for prayer.

His icons, seen in the picture above, are the lily for his chastity, the book and staff representing his authority to preach (supposedly granted to him by a vision of Saints Peter and Paul), and the star above his head. The star was seen by his mother in a vision before he was born; because of it, he is considered the patron saint of astronomers. The last symbol, also seen by his mother in a vision, is the dog with the torch in its mouth, representing that he was to "set fire to the earth" with his preaching. This ties directly to the Dominican connection to the Inquisition, which will get its own post in the near future.

Dominic died on 6 August 1221.

*St. Dominic of Silos (1000 - 1073), who had been abbot of a monastery a few miles from Dominic's birthplace.
**The name eventually given to Dominic's mother was Joan of Aza, and that name was beatified in 1828 by Pope Leo XII.


http://en.wikipedia.org/wiki/Saint_Dominic

Thursday, April 10, 2014

Halley's Comet

Halley's Comet on the Bayeaux Tapestry
The nice thing about astronomy is that some celestial events are so predictably cyclical that they can help confirm dates in history, or be spotted in the historical record. Halley's Comet has appeared numerous times while human beings have been on Earth, and many of those appearances have been noted by record-keepers.

BCE records suggest Halley's was spotted as early as 467 BCE by the Greeks and the Chinese, but the first report detailed enough to be certain of Halley's pattern was in 240 BCE by a Chinese chronicle.

The 1493 Nuremberg Chronicles used many early sources, one of which mentioned the comet appearing over Europe in 684. The 837 approach—recorded by astronomers in Germany as well as across the Middle East and Asia—was the closest the comet ever came to earth: a mere 3.2 million miles away, and took place on 10 April. The Annals of Ulster—an Irish chronicle extending from 431 to 1540 CE—says of 912 "A dark and rainy year. A comet appeared."

1066 saw the appearance of an invading Norman army in England and the appearance of the comet in the Anglo-Saxon Chronicle, in the Irish Annals of the Four Masters, and later in the Bayeaux Tapestry.

Drawing and note from Eadwine Psalter
The Bayeaux Tapestry wasn't the only attempt to record visually what they saw in the sky. The 1145 appearance was drawn up by a monk, Eadwine, who was copying a psalter at Canterbury Cathedral. On the bottom of the page with the Fifth Psalm, Eadwine added a drawing and a note: “Concerning the star ‘comet’. The star ‘comet’ has a ray such as this, and in English it is called the long-haired star.* It appears rarely during the course of many years, and then as a portent.”

The next appearance of Halley's is scheduled for 28 July 2061.

*comet is from Greek and means "hair" or "long hair."

Tuesday, January 28, 2014

Abd al-Rahman al-Sufi, Astronomer

MS. Marsh 144, fol. 135v, Bodleian
The contributions of the Muslim world to astronomy are many, and I have only briefly touched on some of them (such as here). There were nine Muslim astronomers in particular who made major contributions. One of them was the Iranian Abd al-Rahman al-Sufi (7 December 903 - 25 May 986). His name indicates that he was a Sufi Muslim, like Rumi.

al-Sufi translated and expanded on the work of the Greeks, especially attempting to reconcile the Greek and Arabic star charts and constellations. In 964 he published Suwar al-Kawakib al-Thabitah, the "Book of Fixed Stars."* In it he gave the latitude and longitude of hundreds of stars for the year 964 from two views: from both the exterior and interior of a celestial globe. The oldest surviving manuscript known is in the Bodleian Library and was created about 1009 by al-Sufi's son. There was no English translation of this book until 2013.

Among the "firsts" that can be credited to al-Sufi's work are the following identifications:
Ursa Major
  • "the little cloud" that we call the Andromeda Galaxy.
  • the Large Magellanic Cloud*
  • the Omicron Velorum star cluster
  • a "nebulous object" in Vulpecula, now called "Al Sufi's Cluster"
He also describes the astrolabe and lists a thousand uses of it.

The significance of al-Sufi's work led the astronomical community to name other objects after him, such as a a lunar crater (Azophi) and 12621 Alsufi, a minor plant in the asteroid belt with a period of 2000 days.

*There is an argument that he could not have known of the Magellanic Cloud until the same time as Western European astronomers in the 15th century because of its position in the Southern Hemisphere.

Thursday, November 7, 2013

Medieval Meteors

Woodcut showing meteorite coming to Ensisheim.
Today is the anniversary of the first meteorite the exact date of whose fall to Earth has been recorded. It was in 1492, around noon, when a young boy heard an explosion and observed a rock fall from the sky, burying itself in a wheat field outside the town of Ensisheim in what is now France (but was then Austria). The sound of the explosion was heard up to 150 kilometers away. Townspeople came to investigate and found a 127-kilogram triangular rock in a pit a meter deep. They retrieved it from its trench and immediately started chipping pieces from it, until a local authority stopped them, ordering the rock to be delivered to the steps of the local church and preserved pending an investigation.

But that was far from the first meteor or meteorite recorded.* The Journal for the History of Astronomy in 1978 published "Meteors, Meteor Showers and Meteorites in the Middle Ages: From European Medieval Sources." The article lists every meteoritic phenomenon it could find by carefully scouring historical texts, and includes items such as:
453 or 454 — Tres magni lapides (three big stones). Three meteorites fell in Thrace 
518 — Alius ignis . . . instar scintillarum (another fire sparklike). A meteor. Date uncertain. Theophanis Chronographia 
557 — Discursus stellarum (moving stars). A shower lasting the whole night that caused terror. Date uncertain. G. Cedrenus
There are several pages of entries. Meteoric phenomena could be seen as good or evil, often depending upon their proximity to events in the lives of the observers.

As for the Ensisheim Meteor, it currently resides in the Ensisheim museum and is toasted every year by The Brotherhood of Saint-Georges of the Guardians of the Meteorite of Ensisheim. Maximilian I (1459-1519), son of Holy Roman Emperor Frederick III, visited the rock shortly after its fall and declared it a wonder from Heaven. He took some chips for himself and a friend. After years of people taking parts of it away, the rock is now roughly spherical and has been reduced to about 56 kilograms. I guess everyone wanted to have their little piece of Heaven.

*A meteor (first coined in the 16th century, from a Greek word meaning "lofty") is a rocky object that streaks through the atmosphere, heating up via friction and creating a streak of light; a meteorite is a meteor that reaches the ground. A small percentage of meteorites are composed of nickel and iron.

Thursday, October 24, 2013

Cross-referencing an Eclipse

Diagram of an eclipse from a modern translation of Hipparchus
It is not always easy to figure out dates from classical or medieval writings. Chroniclers did not necessarily strive for the kind of historical accuracy which 21st-century audiences expect. When they wanted to be precise, they often expressed themselves in ways that do not provide a proper context for the modern scholar.

Consider, for instance, Pappus of Alexandria, whom the Encyclopedia Britannica calls "the most important mathematical author writing in Greek during the later Roman Empire." [source] He wrote many important texts, but we knew little of his life.

I mentioned the other day how Suidas' Lexicon gives us data on works and events otherwise lost to history. The entry for Pappus reads:
Alexandrian, philosopher, born in the time of the elder emperor Theodosius, when the philosopher Theon also flourished, the one who wrote about Ptolemy’s Canon. His books [are] Description of the Inhabited World; Commentary on the 4 Books of the Great Syntaxis of Ptolemy; The Rivers in Libya; Dream-Interpretations. [source]
We know that Theodosius reigned from 372-395 CE, so it gives us a time frame for Pappus. This creates a small head-scratcher, however. Pappus claims to have calculated and observed an eclipse in the month of Tybi (the fifth month of the Coptic calendar). There is a problem with this dating: no eclipse occurred during the month of Tybi during the reign of Theodosius that Pappus could have observed! Could the Suidas be wrong? Certainly. But then... what is right?

There is, as it turns out, a 10th century copy of a work by Theon of Alexandria (the one mentioned in the Suidas entry) that has a marginal note next to an entry on the Emperor Diocletian (who reigned from 284-305 CE), stating "at that time wrote Pappus." Is it possible that the composer of Suidas had access to that work and assumed that it meant Pappus flourished when Theon did? If we look closer to the reign of Diocletian, we discover that there was an eclipse in the month of Tybi which would place it (using the modern method of dating) on 18 October 320 CE. If Pappus observed it himself in 320, it isn't likely that he was flourishing over 50 years later. This places him firmly in the earlier part of the 4th century.

Pappus is far more important than as an example of the care with which modern historians must date historical events. Some of his eight-volume work on mathematics is extant; and deals with many facets of geometry and carefully lays out the mathematical findings of his predecessors and how their work builds on each other over time. He also worked on several problems such as inscribing regular polyhedrons inside a sphere, conic sections, trisecting an angle, and many more. He has a theorem named after him, as well as the Pappus chain, the Pappus configuration, and the Pappus graph.

His commentary on Ptolemy provides us with insight into some lost works of classical astronomy, such as an astronomical work by Hipparchus on eclipses (illustrated in the above figure).

Friday, February 1, 2013

Nicholas Oresme


Nicholas Oresme (c.1325-1382) likely came from humble beginnings; we assume this because he attended the College of Navarre, a royally funded and sponsored college for those who could not afford the University of Paris. He had his master of arts by 1342, and received his doctorate in 1356. He became known as an economist, philosopher, mathematician and physicist.

One of his published works was:

Livre du ciel et du monde
(The Book of Heaven and Earth)
In this work he discussed the arguments for and against the rotation of the Earth.
  • He dismissed the notion that a rotating Earth would leave all the air behind, or cause a constant wind from east to west, pointing out that everything with the Earth would also rotate, including the air and water.
  • He rejects as figures of speech any biblical passages that seem to support a fixed Earth or a moving sun. (Keep in mind even today we unanimously speak about the beauty of the sun setting when it's really the Earth rising!)
  • He points out that it makes more sense for the Earth to move than for the (presumably more expansive and massive) heavenly spheres and Sun to move.
  • He assures his readers that all the movements we see in the heavens could be accounted for by a rotating Earth.
  • Then he assures the reader that everyone including himself thinks the heavens move around the earth, and after all he has no real evidence to the contrary!
Years later, Giordano Bruno (1548-1600) wrote his theories out in a way so similar to Oresme's that it is assumed he had access to Oresme's writing.

Wednesday, January 30, 2013

Asking Questions

Image from Adelard's translation
of Euclid's Elements of Geometry
Being inquisitive is the first step to learning.* In the early Middle Ages, the presence of many classical authorities circulating in Latin, such as Aristotle and Plato, eliminated the need for inquiry in the opinions of many.

The 12th century saw an influx of more works, many of them Greek writings (preserved by Arabs) or Arab writings. The widening of philosophical and scientific horizons by this wave of knowledge caused many scholars to re-think what had been established.

Adelard of Bath (c.1080-c.1152) was an English philosopher who was in a position to translate into Latin for the first time many of the Greek and Arabic works becoming available to the West. After studying at Tours and teaching at Laon in France, he traveled for seven years through Italy, Sicily, Syria and Palestine. He translated Al-Kwarizmi's astronomical tables and Euclid's Elements of Geometry from Arabic, wrote works on the abacus and on his love of philosophy, and a book called Questiones Naturales (Natural Questions) in which he tackled, in dialogue form, 76 questions about the world. One of his themes is the choice of using reason rather than merely accepting authority.
For what should we call authority but a halter? Indeed, just as brute animals are led about by a halter wherever you please, and are not told where or why, but see the rope by which they are held and follow it alone, thus the authority of writers leads many of you, caught and bound by animal-like credulity, into danger. Whence some men, usurping the name of authority for themselves, have employed great license in writing, to such an extent that they do not hesitate to present the false as true to such animal-like men. [...] For they do not understand that reason has been given to each person so that he might discern the true from the false. [Questiones Naturales, VI]
To be clear: Adelard's science is not ideal: his periodic table of elements contains only four substances, which are mixed in various proportions to create all materials. Some animals see better by day or night because of either white or dark humor in their eyes. We see because an extremely light substance (Plato's "fiery force") is created in the brain, gets out of the brain through the two eyes, swiftly reaches an object and learns and retains its shape, then returns to the brain through our eyes so that we "see" what is in front of us. A mirror, whose surface is smooth, bounces back the fiery force, which on returning to us picks up our image on its way and allows us to see our reflection.

Still, his works were copied and distributed, and influenced much of what was to come. His assertion of reason over blind acceptance of classical authorities was an important milestone in scientific thought. Many of his ideas are seen again in the writings of Robert Grosseteste, Roger Bacon, and Hugh of St. Victor. Once the printing press was perfected, Adelard's translation of Euclid became a standard text for a hundred years.


*One of the followers of this blog is part of a group trying to promote inquiry-based learning in young people. Visit Prove Your World to learn more.

Tuesday, December 4, 2012

Pre-Inertia

Expositio & questiones manuscript
Jean Buridan (c.1300-c.1361) was a University of Paris scholar who was not afraid to tackle some of the big scientific and philosophical issues of the day. That meant, in some cases, taking a critical look at one of the most revered figures in science and philosophy, Aristotle. Buridan, like William of Ockham (c.1288-c.1348),  believed in the observable reality around him, and believed that observation of the world was the key to understanding it. Challenging Aristotle could be risky, but as more and more scholars observed the world around them, they realized that Aristotle's theories needed amendment. He wrote Expositio & questiones (Expoition and questions) to analyze Aristotle's work.

For example, Aristotle believed that an object set in motion—let's say, a rock thrown by a human hand—continues to move after it has left the hand because there must be some continuous external force exerted on it. He theorized that, in the same way a hand swished through water creates little eddies and swirls in the water around it, so the rock's movement is continued by eddies and currents of the air. If there were no movement in the medium that helped carry the rock forward, he believed, the rock would stop its forward course (and presumable drop the the ground). The currents eventually faded, allowing the rock to end its forward flight.

Buridan was not satisfied with this. Building on the work of others (such as John Philoponus and Avicenna, both of whom deserve their own entries some day), he believed that there must be a property in the rock itself that accounts for its action once it has left the motive force of the hand. He called this property of the object impetus (from Latin impetere, literally "to rush toward, to attack").

The property or quality of impetus was clearly changeable. To hurl a heavy rock required you to give it more impetus than to hurl a pebble. Also, impetus was obviously used up over time, allowing the rock to cease its movement and fall. He also explained that a falling object gained impetus the longer it fell (are you paying attention, Galileo?). Unlike Aristotle, who believed that the medium of air in which the object moves helps it along, Buridan saw the air as resistance, causing the object to use up its impetus.

He expanded this theory by looking up. A question had bothered some philosophers for ages: why don't the planets slow down? Will they move forever? Buridan extrapolated his theory to say that a thrown rock in a vacuum would experience no resistance and its impetus would last indefinitely. If the planets were moving in a vacuum...

Well, actually, he couldn't go that far. He agreed with Aristotle that a vacuum couldn't exist in space, since there was no container to keep matter from rushing into the empty area. If above our atmosphere were filled with quintessence, however, Aristotle's "fifth element" that was pure, unchangeable, and frictionless, then the impetus imparted to the planets by whatever initial agency would continue to move forever! The idea of an eternal universe was supportable by science!

Sunday, November 18, 2012

Refuting Astrology

As attractive as astrology was in the Middle Ages, not everyone was willing to accept the premise that it was "easy" to use it for predictive purposes, or even that it was likely that the existence and movements of observable heavenly bodies had a direct influence on events and people on Earth.

We have seen how some sources, such as the University of Paris, spoke against astrology's predictive uses not because it believed they were in error, but because they were believed to contravene God's wishes for human beings. There were others who objected to the reliance on astrology because they could not believe that it was likely to work.

Ibn Qayyim Al-Jawziyya (1292-1350) was a Sunni Islam theologian and commentator on the Qu'ran. Not given to flights of fancy, and accustomed to arguing the details of the law, he put a critical lens on astrology. One of the lynch pins of his refutation of astrology came from the fact that hundreds of stars were not included in astrological calculations. Astrologers told him that the stars were too far away and to small to matter. To Al Jawziyya, this was an intolerable double-standard:
And if you astrologers answer that it is precisely because of this distance and smallness that their influences are negligible, then why is it that you claim a great influence for the smallest heavenly body, Mercury? Why is it that you have given an influence to al-Ra's and al-Dhanab, which are two imaginary points?
Astrologers accepted at the time, through their calculations, that the stars appeared small because they were far away, but were actually enormous compared to the world. They also knew that the Milky Way was "a myriad of tiny stars packed together in the sphere of the fixed stars"; Al-Jawziyya said that it was impossible to know what effect, if any, they would have. Astrology had too many variables, and was just so much guesswork.

What were the "two imaginary points" mentioned in the above quotation? He was referring to "orbital nodes," the imaginary point in space where the line of "an orbit crosses the plane of reference to which it is inclined." Astrologers made much out of these points, which had no physical existence, and yet ignored actual physical stars. They neglected stars as being too small to matter, and yet put all their attention on planets that were a ridiculously small fraction of the size of a star. To the keen legal and theological mind of Al-Jawziyya, this suggested that astrology was not, in fact, based on any kind of rational thinking.

Friday, November 16, 2012

Father of Arab Astrology

Abu Ma'shar, from his Introduction to Astronomy
Albertus Magnus, Robert Grosseteste, Geoffrey Chaucer—well-known names from the Middle Ages denoting a Dominican scientist, a university scholar and administrator, and a courtier and poet. One thing they had in common, besides a love of learning, was their attention to the art of astrology. And through their interest in astrology, they were all influenced by a 9th century Arab known in the West as Albumasar. His full name was Abu Ma'shar Ja'far ibn Muhammad ibn 'Umar al-Balkhi (787-886), and he was one of the most respected figures in the history of astrology.

Abu Ma'shar was of particular interest to Western Europe because he was a source for knowledge of and commentary on Aristotle when his writings reached Europe in the 12th century, brought back by the Crusaders. He offered so much more, however. His work blends knowledge of Greek science with Islamic doctrine, Persian chronology, Mesopotamian astrology, and hermetic traditions from Anatolia. He presented a unified approach to the knowledge of several cultures that lent weight to his work.

For instance, he uses the Biblical Flood as the focal point of his astrological tables. He calculates it at midnight on Thursday to Friday, 17-18 February 3101 BC. This date was not arbitrary, nor was it an indication that Abu Ma'shar believed in a short-lived Earth. He chooses the date because it is the start of the Hindu Kali Yuga (the "age of vice"; the last of four phases the world will go through). His knowledge and acceptance of Hindu chronology and its "Great Year" (composed of 360,000 years) is further shown when he calculated a grand conjunction of planets in 183,101 BC, and again in 176,899 BCE.

The Middle Ages loved "unified theories" that could reconcile different traditions to enhance understanding. Abu Ma'shar argued for the superiority of his chronological calculations because he made the year out to be 365.259 days long. Why was he so enamored of this number? Because "259" he explained was the minimum number of days for human gestation (8.6 months). It was obvious to him that he was onto something!

Unlike the hostility experienced by astrology from the University of Paris and others, who felt it was a way to contravene God's plan, or to know what should remain unknowable, Abu Ma'shar was able to give his astrology a veneer of respectability by acknowledging Islamic religious doctrine.

Wednesday, September 26, 2012

The Father of Modern Optics

For a long time, there were two competing theories about how the eyes see—both wrong.

Alhazen ibn al-Haytham
Aristotle believed in what is called the intromission theory: the idea that actual physical forms enter the eye to plant images in your head. Euclid and Ptolemy believed in the theory of extromission: the idea that rays from the eyes went out and "scanned" or "detected" objects. Scholars and philosophers for centuries came down on one side or the other. It wasn't until the 11th century that a better theory came along.

Alhazen ibn al-Haytham (965-c.1040) was a Muslim who wrote about many topics. Originally he was a theologian, trying to address and reconcile the issues between the Shi'ah and Sunnah sects. He made his most lasting contributions, however, in the fields of astronomy, mathematics and optics. His Kitab al-Manazir (Book of Optics) changed the study of optics forever. He rejected both previous theories, arguing that there was no time for the eye to emit rays that could travel to a distant star and back to the eye instantly the way they would have to when first opening the eyes. He also refused to believe there was any mechanism that allowed forms to enter the eye. Instead, he opted (ha ha) for light coming from external objects to enter the eye, carrying an image of the object being looked at.

His theory of light's involvement in sight came when he realized that bright and dim light both affected visual perception, and that bright light left after-images on the eye. Also, it was obvious that perceiving color depended upon having sufficient light. He even invented the camera obscura in order to learn more about how light worked.

...and he did it while in prison.
Alhazen's diagram of the eye, with terms we still use

Earlier in his career, he became overconfident in his knowledge and made the mistake of claiming it would be possible to devise a way to control the annual spring flooding of the Nile. (Although born in Basra, Iraq, he lived his adult life in Cairo.) Hearing this, Caliph al-Hakim bi-Amr Allah, the sixth ruler of the Fatimid dynasty, ordered him to do so. When al-Haytham realized he wasn't able to perform this enormous feat of engineering, he tried to simply retire from the profession. The angry Caliph sent his men for al-Haytham, who feigned madness in order to avoid a death sentence for disappointing his all-powerful ruler. He was placed under house arrest, and devoted the remainder of his life to the sciences for which he is now known. Because of the experiments he conducted in order to test his theories, mirroring what would be known as the scientific method, some think of him as the "first scientist."

Monday, September 24, 2012

Hermann of Reichenau

Hermann, with crutch & Salve Regina
Hermann of Reichenau (1013-1054) was born to Count Wolverad II and his wife Hiltrud in Upper Swabia. He was severely disabled at birth, and had to be carried around in a specially built chair. A 1999 article tried to diagnose him based on contemporary reports.
Using the biography written by his disciple Berthold, [an] unbiased analysis of the symptoms described [...] is worked out: [...] Intellectual functions were unaffected. [...] Muscle disease is considered possible, but motor neuron disease - either amyotrophic lateral sclerosis or spinal muscular atrophy - seems to be the most convincing diagnosis. [C Brunhölzl, Thoughts on the illness of Hermann von Reichenau]
Because of his condition, he was nicknamed "Contractus" or "the Lame." When he was seven years old, his parents handed him over to the cloister school of the nearby Benedictine monastery on Lake Constance, where he studied under Abbot Berno. Berno was a well-known figure at the time for, among other things, his reforms in liturgical music. Hermann became a monk in 1043 and, upon Abbot Berno's death in 1048, became Berno's successor as abbot.

Despite Hermann's extreme difficulty in moving and even speaking, he was considered a devoted monk and brilliant scholar. He wrote a great deal on music, mathematics, and astronomy. As well as a treatise on the science of music, he wrote two of the best-known of the medieval liturgical songs, the Alma Redemptoris Mater (Loving Mother of the Redeemer), and the Salve Regina (Hail Holy Queen).*

Among his other accomplishments, he is credited with speaking Arabic, because through his writings he made available to the Latin West many scientific discoveries that were previously only widely known in the Arab world. This knowledge of Arabic, however, is only an assumption. His biographer, Berthold, never mentions knowledge of Arabic, which would be unusual omission for such an accomplishment. The monastery was a center of learning in the area, and very likely held copies of works by Gerbert of Aurillac, who learned much from Arabic sources in Spain.

Hermann wrote two works on the astrolabe, previously unknown in Europe, and described a portable sundial. His works on mathematics used Roman numerals. Although this precluded the use of decimals, he still achieved some remarkable results. In his Epistola de quantitate mensis lunaris (Letter on measurement of lunar months), he tries to find the average length of a lunar month. In decimal notation, it is 29.530851 days. Hermann did not only not have decimal notation, he didn't have minutes and seconds. In his time, the hour was divided into "moments" and "atoms." He calculates the length of the lunar month to be 29 days, 12 hours, 29 moments, 348 atoms, which turns out to be exactly right.

He also wrote a history called Chronicon ad annum 1054 (Chronicle to the year 1054). The original is lost, but a 1529 edition saved the unique historical knowledge inside. After Hermann's death, it was continued by Berthold; Berthold died in 1088, but the duty was taken up by others up until 1175.

Hermann died on 24 September. In 1863, he was beatified (a step toward being recognized as a saint). As Blessed Hermann of Reichenau, he is considered the patron of unborn babies, and his Feast Day is celebrated on 25 September.

*A popular English version of Salve Regina was prominent in the Whoopi Goldberg film "Sister Act."

Sunday, September 23, 2012

Autumnal Equinox Lightshow

Holy Trinity Church in Barsham, Suffolk
The equinox, from Latin aequinoctium (the time of equal days and nights), the day twice each year when the amount of daylight and darkness equalizes. We are used to marking the solstices, because the longest day of sunlight and the shortest day in winter carry real-life significance for us. But the equinoxes in spring and fall rarely get the same attention.

But in Suffolk, England, in Holy Trinity Church in the tiny town of Barsham, the equinoxes have provided a special show since the Middle Ages—if one knew where to look.

To be truthful, the "special show" was forgotten for a long time because of some changes. Holy Trinity is an early church, using stone from Caen that tells us it was built post-1066, although the round tower is by many considered to be an earlier Saxon style. The church suffered when Henry VIII broke with Rome and made changes consistent with the new Anglican Church. A rood screen, an ornate partition between the main part of the church and the nave behind the altar, was torn down, and the large crucifix that hung on it was eliminated. In 1870, however, the vicar of Holy Trinity decided to rebuild the rood screen and restore the crucifix to the same spot it hung in centuries earlier. Unfortunately, the vicar also decided to hang a large painting over a narrow west window whose significance he did not realize.

On the equinoxes, light strikes the crucifix for 4 minutes
Then, in 1979, a fire destroyed the nave roof. During the reconstruction, someone took the painting down. Years later, during a mass at dusk on the autumnal equinox, someone saw it. Now that the church was restored to its original configuration, the narrow western window throws a shaft of light for 4 minutes each equinox—and only on the equinox—right onto the crucifix near the top of the rood screen.

It was easy to miss for several years: it doesn't show when there is cloud cover at twilight, and you need to be looking up. Now that the phenomenon has been re-discovered, however, the church is filled each equinox by people waiting to see the fascinating result of an unknown medieval architect who decided to use light to illuminate his art.




Wednesday, September 5, 2012

Phantom Time

In June 2005, at a conference in Toronto on "Anomalous Eras - Best Evidence: Best Theory," Heribert Illig presented a paper he called "The Invented Middle Ages." It was not the first time this theory of history had been presented to the public—it had been known in Germany since 1996—but the first time it had been presented outside of Europe. In it, he explained his path to finding an anomaly in the historical record: that 300 years of our history did not exist! This theory is called the "Phantom Time Hypothesis."

Illig was born in 1947 in Germany. He studied economics, mathematics, physics, some art history and Egyptology, and describes himself as "not a historian in the narrow sense of the word." While reading the theories of Immanuel Velikovsky (that Earth has barely survived closes passes by Venus and Mars, before they settled into their present orbits, and that these fly-bys took place within the memory of ancient man and were recorded as myths), he began to question the historical record in Egypt, which led him to co-author a book, Wann lebten die Pharaonen? (When Did the Pharaohs Live?).

Diagram of missing and "recalibrated" years.
Once he was comfortable with questioning the accepted history of the human race, he started looking at the Middle Ages. He asked himself questions. Why did certain documents with earlier dates only get discovered later? How far off might the calendar have been by the time Pope Gregory insisted it be fixed? Could the engineering of Charlemagne's time really produce a building like the Chapel of Aachen, which looks to be part of Romanesque architecture style, which only existed two centuries after Charlemagne? As for Charlemagne himself: did he really create a re-birth from 768-814, when everything on either side of him is still "dark," and could one man possibly have done all that scholars say he did? How much can we trust those periods in western Europe that we now call "Dark Ages"?

His conclusion: there is a gap of years, from 614 to 911, for which any dates and events ascribed did not in fact take place. Essentially, a 300-year span has been "presumed" by historians who have tried to make sense of the unclear and inaccurate data we have; methods of radiometric and dendrochronological dating are unreliable, et cetera. Others have picked up on this and added to it; of course, he also has his opponents.

Illig has to assume enormous errors on the part of archaeologists and historians, as well as an elaborate conspiracy taking place in the centuries after 911 to "record" history that took place in the three centuries previous. Some of his arguments result from his misunderstanding of Gregorian calendar reform and dating methods. Some are just assumptions that contemporary witnesses are untrustworthy.

Is there a chance he's right? Is it possible that we are living in the year 1715 CE? Fortunately, astronomy helps. The Persian Wars between Greece and Persia lasted from 499-449 BCE.* The Greek historians of the wars tell of two solar eclipses taking place not far apart. The only times for two solar eclipses near each other in that part of the world were 2492 years ago and 2490 years ago, on 2 October 480 BCE and 14 February 478 BCE.

So there it is. No missing time. Thanks, science!

*One of these battles, Marathon, is remembered in the present day in footraces across the world. Another battle, Thermopylae, gave us the plot for the movie "300."

Friday, August 3, 2012

How far are the stars?

Rabbi Levi ben Gerson, also known as Gersonides, lived from 1288-c.1344. He was from a family of scholars: his father, Gerson ben Solomon of Arles, was the author of the Sha'ar ha-Shamayim, an encyclopedia of natural science, astronomy, and metaphysics.* Levi is credited with first mentioning, and possibility inventing, Jacob's Staff. (He references Genesis 32:10 when he describes the device; this is likely the origin of the name.)

At a time when religion, philosophy, astronomy, astrology and science were overlapping (and in some cases, interchangeable), Gersonides' greatest work, which was philosophical, contained his greatest contribution to astronomy. He put twelve years (1317-28) of effort into the Milhamot Adonai ("Wars of the Lord"), whose six books dealt with 1) the soul, 2) prophecy, 3) & 4) god's knowledge of facts and providence, 5) astronomy/astrology, and 6) creation and miracles. Gersonides firmly accepted astrology and the celestial hierarchy of powers inherited from neo-Platonists and pseudo-Dionysius (far too complex to go into here), but he also brought mathematics and observation to his work with extraordinary results for the time.

Postage stamp honoring Gersonides.
Gersonides rejected the Ptolemaic system of epicycles to explain the erratic motion of planets affixed to their crystal spheres surrounding the Earth. According to Ptolemy, epicycles explained the changing size of planets; he said, however, that Mars varies by a factor of six; Gersonides' observations told him that Mars's apparent size varies only two-fold. Gersonides used the Jacob Staff and a camera obscura (pinhole camera) to make careful observations over several years. For Gersonides, 48 crystalline spheres were needed to explain the apparent motion of various heavenly bodies. This expansion of the "physics" of the Ptolemaic model was nothing, however, compared to the actual physical expansion he proposed.

Careful observation with the Jacob Staff, the camera obscura, and math made Gersonides declare heavenly objects to be much farther away than previously calculated. Ptolemy claimed the distance to Venus was 1079 Earth radii; Gersonides estimated it to be 8,971,112 Earth radii away. Ptolemy said the fixed stars were 20,000 Earth radii away; Gersonides estimated them to be at a distance 10 billion times greater.

Pope Clement VI had the "Wars of the Lord" translated into Latin in 1344, making it available to the west. Its impact was minimal, however; we know of a few scholars who were influenced by it, and Kepler asked a friend to send him a copy in the 17th century. But it took Copernicus two centuries later to "confirm" to Western civilization's satisfaction that Gersonides was on the right track.

*As I have mentioned about medieval encyclopediæ before, they were often compilations of previous works; this one drew from Claudius Ptolemy's Almagest and the Morah Nebukim, or "Guide for the Perplexed" of Maimonides. A 1547 edition of ben Solomon's work can be had from Kestenbaum & Company.

Tuesday, July 31, 2012

Jacob's Staff

Have you seen a modern surveyor using a single vertical rod with an instrument on top to measure property lines? That pole is nicknamed a "Jacob's Staff." Hundreds of years ago, however, the term "Jacob's Staff" was used to refer to more than one type of instrument; it's the other instrument that I want to discuss today.
A recreation of a Jacob's Staff.

The other instrument was also called a cross-staff, or a fore-staff, or (around the Mediterranean) a balestilha. It comprised a staff with cross-pieces designed to allow the user to determine angles of distant points. By aligning it with, say, Polaris (the North Star), a sailor could determine the angle between the star and the horizon. Matched against known measurements, the sailor then knew his latitude.

Knowledge of geometry and arithmetic also allowed the user to determine other measurements. If the height of a distant tower were known, that number and the angle known via the staff allowed you to determine your distance from the tower. Alternately, if you knew your distance from the base of a tall object, finding the angle from you to the top of it helped you determine how tall it was.

The Jacob's Staff had another name as well when used with heavenly bodies: radius astronomicus.

From an early book on navigation.
Where did it come from? The earliest description we have of the device is in the astronomical works of Gersonides (Levi ben Gerson, 1288-1344), who describes it as:
... a staff of 4.5 feet (1.4 m) long and about one inch (2.5 cm) wide, with six or seven perforated tablets which could slide along the staff, each tablet being an integral fraction of the staff length to facilitate calculation, used to measure the distance between stars or planets, and the altitudes and diameters of the Sun, Moon and stars. (Book of the Wars of the Lord)
Although some ascribe it to a contemporary of his, an astronomer named Jacob ben Machir (1236-1304). This might also explain its common name, since no other convincing etymology has come forth. The invention of the more precise sextant in the 18th century rendered the Jacob's Staff a quaint relic, and the name, when used, came to refer only to the simpler measuring stick we still see today.