Solar Eclipses & History Part 2: What a drag! Archilochus & the Ugaritic tablets

Types of Eclipses

There are three types of eclipses – depending on the alignment of the Sol, Luna, and Earth as well as the position of Luna in its orbit.     Just as Earth’s orbit around Sol is not a circle, Luna’s orbit around Earth is similarly eccentric and also varies a bit over time due to tidal interactions.   Also, Luna’s orbit is inclined to the ecliptic by about 5° so it is relatively rare that Earth, Sol, and Luna are in a straight line at full or new moons.     If the Moon is further from Earth in the same circumstance, it will not appear to be big enough to cover the entire sun – leaving a ring of Sol still visible.   This is called an Annular eclipse. As you can see in the above photo, the sky is not completely dark.    If Luna is closer to Earth in its orbit and comes directly between Sol and Earth, it will appear to cover the entirety of the Sun for a ‘Total’ eclipse.    Only then will the sky go dark – a somewhat rare and special event.   In a given spot on Earth (never more than around 170 miles [275km] in width), the event will last around 8 minutes.

When is a Day not a Day?

“We have more old historical records of eclipses than we have old astronomical observations of the moon.”   In the Johns Hopkins APL Technical Digest, Volume 6, Number 2 (1985), Robert R. Newton gives a great description of the perils of connecting historical eclipse records with astronomical records.   In the study of ancient cultures and deep history, eclipses can provide invaluable clues to the timing of an event or reign.    Unfortunately, it is not as simple as it might seem.    You can use records of a historical eclipse to help determine how the motions of the Moon and Earth have changed over time.   Or, you can calculate in reverse when an eclipse should have happened to find the date of historical events.    Both of these are done, but you can see the problem…    It ends up being a logical circle.     Prior to about 1000 AD, margins of error become larger and larger.    Why, you ask?

One major reason is that tidal friction from Luna is slowing Earth’s rotation.    Unlike early astronomers, we now know that a day is not a constant amount of time.   Accounting for conservation of momentum, the moon is slowly moving away from Earth, making both the day and the month slightly longer – a movement originally confirmed by looking at the growth of corals and later confirmed by pointing lasers at the mirrors left by the Apollo lunar missions.  (to me the absolute best proof the Moon landings were not a hoax, but that’s another story…)  This variation is not perfectly linear or constant, but Newton (1985) suggests that Earth’s spin has slowed since 500BC.     When you are looking at an event like an eclipse that lasts only minutes, even a slight change in the rotation of the Earth can change where the region of an eclipse occurs by miles.    The early practice was to assume a value for the lunar acceleration and then use this value to calculate past eclipses and then match it to the closest historical account of an event to re-date it.

Archilochus

A good example of this is in the poetry of Archilochus (680-645BC), which almost certainly describes a total solar eclipse.     He wrote:

Bust of Archilochus

 

“Nothing is unexpected, nothing is foresworn and
Nothing amazes now that father Zeus the Olympian
veiled the light to make it night at midday
even as sun was shining: so dread fear has overtaken men.
From this time on everything that men believe
will be doubted: may none of us who see this be surprised
when we see forest beasts taking turns in the salted field
with dolphins, when the echoing waves of the sea become
Dearer to them than the sand, and the dolphins love the wooded glen…”

But, when and where did this observation happen?     Archilochus split his life between two islands in the Aegean.    It is known that right around that time the Greeks from Paros formed a colony on Thasos. (AJ Graham, The Annual of the British School at Athens, Vol. 73 (1978), pp. 61-98.)    Born into poverty on Paros, Archilochus served as a soldier initially on Thasos then returned to Paros to defend the island from Naxos.   (from The Cambridge History of Classical Literature: Volume 1, Greek Literature, 1985 p. 117-127)

As I said above, solar eclipses are a rare event so you’d think that you could work backwards and easily find the answer.    Initial reverse calculations by von Oppolzer (in Canon of Eclipses, 1887 – Sitzungsberichte, Vienna Academy of Sciences) put the date of Archilochus’ eclipse in April 648 BC. [translated by Lynn, 1893 / The Observatory V. 16]    But if this date is correct, we’d need to change Archilochus’ birthdate as it is unlikely he wrote the poem at age three.    And, according to von Oppolzer’s chart, the eclipse shadow would have missed both islands!   So, is the problem with the ancient Greek records or with the astronomical calculations?   And – as they are nearly 1000km apart – on which island did it occur?

In ‘Memoire della Societa degli Spettroscopisti Italiani’ (April 1893), Millosevich [translated in Lynn 1893] recalculated and suggests two possible dates (657BC and 648BC) and only one of them would have been a total eclipse.  His calculation matched von Oppolzer 648BC date but shifted the location showing that on April 15, 648, a total eclipse occurred over Thasos.     Case closed…?    Should we trust the eclipse calculations over the Greek records?

Unfortunately, not so fast.    Newton (1985) shows that because of the changing speeds of the Earth/Moon system – depending on what values you assume, the eclipse could have been visible from either island!

This is one well known example, but many similar stories exist.

Ugaritic Tablets

Another interesting example are the Ugaritic clay tablets discovered in 1928.    One of these tablets [translated by Sawyer 1928 in the Bulletin of the School of Oriental and African Studies 33 (1970)] says

Ugarit tablet

“The day of the new Moon in the month of Hiyar was put to shame.
The Sun went down (in the daytime) with Rashap in attendance.”

It seems likely that this refers to another total eclipse of the Sun.    Hiyar was the 2nd month of the year and roughly corresponds to our April/May.   Using some basic deductions, Stephenson [Nature v228, p. 651-652] concludes that this must have occurred in one of four dates (July 1406, May 1375, Jan 1340, and March 1223) – ultimately deciding on 1375BC.   He says it is the earliest known record of a solar eclipse.  [note:  this is modern day Syria]

Twenty years later, the text was retranslated by van Soldt.    His retranslation is described in Nature v. 338 (Jong and van Soldt, 1989) and includes a reference to the planet Mars being visible during the eclipse.    The article goes on to explore the Ugaritic calendar (including a reference to a Damascus research document discussed in as yet unpublished research by van Soldt) and conclude that March is a more accurate correlation for the month of Hiyaru.    They ultimately decide that the March 1223 date must be correct as both the month matches and it is the only one of the four ‘Stephenson’ eclipses where Mars would have been visible.    With that established, they then use that date to calculate the deceleration of Earth’s rotation and find that it is consistent with values established by the lunar ranging experiment.

So, historically, what difference does 150 years make?    Well, in the case of Ugarit, there were at least nine different rulers between 1375BC and 1223BC!   (You’ll forgive the wiki reference here, I’m admittedly being lazy – https://en.wikipedia.org/wiki/Ugarit)    That’s a significant change in context for when the tablets may have been created!

The Bottom Line

The bottom line is that while both history and astronomy mutually benefit from the accurate identification of ancient eclipses, there are a host of variables that make such identifications difficult.   It also really shows the value of the lunar ranging experiments!      Maddox (Nature, v313, 1985) gets to the heart of the matter saying:

“In spite of arguments about the astronomical identification of ancient eclipse records – one thing is certain…
The more that can be found, the more useful they will be.”

The second take away point is that total solar eclipses will one day be only a memory.     As the Moon is progressively moving further away from Earth, it will become smaller and smaller till one day it can no longer cover the Sun.    I wouldn’t worry though; this article suggests it won’t happen for at least another 590 Million years!

Part 2:  Eclipses & Metaphors coming soon!

ps.   I am going to state right out that I am not an “expert” in ancient Ugaritic or Greek history or advanced celestial mechanics (or much of anything).    My goal with these articles is to simply show some of the connections between history and eclipses in a way that everyone can understand.   It also gives me some much needed practice doing research!   (something I’ve been missing…)    I welcome input.