The Lunar Eclipse

The Annals of Clonmacnoise have an entry for 670 that reads "The Moone was turned into a sanguine collor this year." A red moon usually means a lunar eclipse. During a lunar eclipse, the Earth passes between the sun and Moon, causing the light on the Moon to appear sanguine, or blood-red.

The mechanics of eclipses were understood long ago. Babylonians over 3000 years ago had eclipses figured out, and even Isidore of Seville in the 7th century understood the process. (The illustration is a 14th century book showing the phases of eclipses.) Isidore knew that the lunar eclipse would only occur when the Moon was full.

Not everyone knew that this was a predictable and understandable phenomenon, however. A solar eclipse took place on 23 June 1191 in England, and the monk Richard of Devizes commented that those who saw it and did not know what scholars knew thought it was a sign of something ominous. Earlier, a lunar eclipse during the First Crusade showed a blood-red Moon over Jerusalem as the Crusaders approached. It was described as a sign of God's will. (This was reported later by Albert of Aachen, writing a history of an event he did not himself witness. Albert had no compunction against stating that a lunar eclipse portended a defeat for the Crusade's enemies, while a solar eclipse would have meant disaster for the Crusade.)

John of Salisbury warned against using eclipses as signs of future success or failure. Astronomy was fine, but using it to predict the future was as erroneous as soothsaying, astrology, and other such practices.

Bishop Thietmar of Merseburg also proclaimed that eclipses were not caused by evil incantations or the celestial bodies being eaten by demons or monsters. This is the only reference to the idea of the sun or Moon being "eaten" during an eclipse. We can't be sure if anyone really claimed this, or if Thietmar was just exaggerating the fears of the uneducated so that he could counter them.

An eclipse in 756 was described by Simeon of Durham in some detail:

Moreover, the Moon was covered with a blood-red color on the 8th day before the Kalends of December [i.e., November 24] when 15 days old, that is, the Full Moon; and then the darkness gradually decreased and it returned to its original brightness. And remarkably indeed, a bright star following the Moon itself passed through it, and after the return to brightness it preceded the Moon by the same distance as it had followed the Moon before it was obscured.

Simeon seems to be describing the occultation of a star during the eclipse.

John of Salisbury has been mentioned here before, but he said and did a lot that deserves attention. We'll look at him next time.

Who Invented the Mechanical Clock?

In researching the previous post, I came across a reference to Pope Sylvester II (formerly Gerbert d'Aurillac, c.946 - 1003) inventing the mechanical clock. The source of this was the William Godwin's final book, Lives of the Necromancers, An Account of the Most Eminent Persons in Successive Ages Who Have Claimed for Themselves, or to Whom Has Been Imputed by Others, The Exercise of Magical Powers [1834]:

This generous adventurer, prompted by an insatiable thirst for information, is said to have secretly withdrawn himself from his monastery of Fleury in Burgundy, and to have spent several years among the Saracens of Cordova. Here be acquired a knowledge of the language and learning of the Arabians, particularly of their astronomy, geometry and arithmetic; and he is understood to have been the first that imparted to the north and west of Europe a knowledge of the Arabic numerals, a science which at first sight might be despised for its simplicity, but which in its consequences is no inconsiderable instrument in subtilising the powers of human intellect. He likewise introduced the use of clocks. He is also represented to have made an extraordinary proficiency in the art of magic; and among other things...

The italics are mine. A little further along, Godwin adds a footnote that tells us his information comes from William of Malmesbury. William (c.1095 - c.1143) was the foremost English historian of the 12th century. Not exactly a contemporary, but maybe near enough that the memories and stories were still fresh? It would be difficult to determine the accuracy of this report, especially in the context of a brief blog post. Fortunately, I don't have to.

As it turns out, Marek Otisk of the University of Ostrava (Czechoslovakia) published an article on this very topic in September 2020, Gerbert of Aurillac (Pope Sylvester II) as a Clockmaker. He examines the reports from William of Malmesbury, the Chronicle of Thietmar of Merseburg (died c.1018), and a much later record (someone who died in 1610). Among his detailed examination of these and other historical records we learn that although William claims Gerbert built a clock in Reims, a friend of Gerbert's (Richest of Reims), writes about Gerbert's stay in Reims in detail and never mentions a clock. Otisk concludes that William's ascribing of the creation of a clock to Gerbert cannot be trusted.

The later report by the Benedictine monk Arnold Wion, who died about 1610, claims Gerbert built a clepsydra, a water clock, in Ravenna. What we know of Gerber's time in Ravenna, however, is that it was very short; again, no contemporary accounts support this story.

Thietmar of Merseburg tells a different story, that Gerbert created a clock in Magdeburg. Thietmar was a bishop and close friend of Holy Roman Emperor Henry II, who succeeded Otto III, credited with making Gerbert into Pope Sylvester II. Thietmar's Chronicle includes a specific detail about Gerbert creating, in Magdeburg, "created clocks (horologium) which he correctly calibrated according to the Polar star (stella, dux nautarum) which he observed through an observation tube (fistula)." [Otisk, p.32] Otisk likes this account because both Thietmar and Gerbert were in Magdeburg in the late 990s, and very likely crossed paths several times.

The use of the word horologium is misleading, however. We use it for the word "clock," but it is more likely that Gerbert was creating a calibrated armillary, or possible even an astrolabe, which he knew about from his exposure to science being done by Islamic philosophers.

So I can't tell you who created the first mechanical clock. But the question of horologium remains: when long-ago writers refer to "clocks," what exactly did they mean? What constituted a clock? There were several ways to measure time without staring at the sun and judging, and I'll talk about those devices tomorrow.

Eclipse in 828

A lunar eclipse was recorded for July 1 in 828 very early in the morning. A second one occurred on Christmas Day, and was recorded thusly in the Anglo-Saxon Chronicle:

In this year the Moon was eclipsed on mid-winter's Mass-night, and the same year King Ecgbert subdued the kingdom of the Mercians and all that was South of the Humber.

Note the lack of panic, such as we expect from Hollywood's portrayal of technologically primitive people experiencing an eclipse. Even if your theory of the heavens were no more sophisticated than perceiving heavenly bodies as balls of light affixed to concentric crystal spheres, you would realize that they could simply overlap at times. The Babylonians and Greeks had figured out the patterns of eclipses centuries earlier than the Anglo-Saxon Chronicle, and Isidore of Seville (c.560-636) in his Etymologies (which was used throughout the Middle Ages the way we would use an encyclopedia) explained

"The moon suffers an eclipse if the shadow of the earth comes between it and the sun" while an eclipse of the sun takes place "when the new moon is in line with the sun and obstructs and obscures it."

While Medieval Europe had Isidore to explain what was happening, however, they did not necessarily have the knowledge of the Babylonians and Greeks to understand why it was happening. The event could still be unnerving. Bishop Eligius of Noyon in the 7th century warned: "When the moon is darkened, no one should dare to utter shouts, because it becomes dark at specific times at God's command." Hrabanus Maurus (c.780-c.856), another encylopedist, tells of a lunar eclipse when some threw spears toward the moon, trying to defend it from its attacker.

Even if the mechanism of eclipses was understood, people might still accept them as a sign of great portent, or as the result of human actions. Bishop Thietmar of Merseburg, referring to an eclipse of 990, wrote "I urge all Christians that they should truly believe that this does not happen on account of some incantations by wicked women, nor by eating, and it cannot be helped by any action in the world."

Oh, and when Astronomy Today tells you that the eclipse of May 5, 840 so frightened King Louis that he "died just afterwards"? Ask to see their sources. Louis died on June 20th at the age of 62, after years of quelling civil wars. I think there are likelier reasons or his death than being afraid of an eclipse.