SciFoo 2010: tales from an unconference

6. August 2010 09:56

Sci Foo logo

Wow. I just got back from Sci Foo camp, a meeting of over three hundred people from all areas of science held at the infamous Googleplex in Mountain View, California. Whereas most science conferences tend to be focused around a particular topic, this was an unconference (inspired by similar events held in the technology industry), organised by Google, Nature and O'Reilly Media. There was no theme, no schedule, and no rules particularly except that we were encouraged to attend sessions that we knew nothing about, and talk to people we didn't know.

As well as scientists from all areas there were lawyers, journalists, bloggers, filmmakers and philosophers. History of science was also well represented, with attendees including Will Noel of the Archimedes Palimpsest project, Tilly Blyth, curator of computing at the Science Museum, Nigel Warburton, creator of the excellent Philosophy Bites podcast and Bonnie DeVarco, who for many years was chief archivist for the Buckminster Fuller archive, but is now involved in exploring visualisation technologies. There were also plenty of demos, including a lego model of the Antikythera mechanism made by Andrew Carol, which I'm hoping to write about in a future post.

The result was a fascinating weekend - I ended up in discussions about everything from how virtual reality technologies will affect children's brains, to the end of gravity as we know it. I blogged the event for New Scientist, so rather than repeat myself, here are links to all my posts from the meeting:

Lego to loo seats: an unconference at Google HQ

Are you ready for life in world 3?

Evolution of music and a dancing cockatoo

Rewriting gravity over a tuna roll

And here are some other attendees' posts that I enjoyed:

Letter from SciFoo: The joys and sorrows of the unconference (Carl Zimmer)

Correspondent's diary: Around the campfire (The Economist)

Sci Foo 2010 Un-conference at Googleplex (Nigel Warburton)

Even more links are collected here.


A modelmaker's work

30. July 2010 17:10

Michael Wright in his workshop

Just a quick post to let you know about a new web page dedicated to the Antikythera mechanism - in particular the work of curator and mechanic Michael Wright (pictured). He spent many years studying the surviving pieces of the Antikythera mechanism, and built a working model that is pretty much universally recognised as a work of genius in itself. Now physicist and science historian Fabio Soso has collected together various material including papers, talks and interviews. Wright doesn't have his own website, and sometimes his work doesn't get as much media coverage as other research on the mechanism, so Soso says he has created the web page to make sure that Wright gets full credit for everything that he has done. Highlights of the collection include a beautiful computer animation of the gearing inside the Antikythera mechanism, which I've written about here.)


Earth-like planets everywhere

28. July 2010 11:47

The Earth as seen from Apollo 17

There's a fascinating talk up on the TED site this week by Dimitar Sasselov, a Harvard astronomer working on NASA's Kepler telescope, which is searching the skies for planets similar to our own. The telescope was launched in March last year. Until now, most of the planets spotted outside our solar system have been very large and orbiting very close to a star - nothing like Earth - just because those are easier to spot. We didn't have any idea how many Earth-like planets might be out there. And these are the ones that most people are interested in because they've got the best chance of being habitable...

The Kepler team announced their first results in January this year, but didn't include information on Earth-like planets. So Sasselov gives the first glimpse of what might be out there in his talk, which was given earlier this month and posted (I think) yesterday. He emphasises that most of the finds so far are candidates and will need to be confirmed with further tests (so far the mission has officially confirmed only 5 planets). But what's interesting is the distribution of sizes of the planets being found. About half-way through his talk, Sasselov shows a chart with about 250 planet candidates categorised by size, of which about 140 are Earth-sized (ie with a diameter less than twice that of Earth).

"The statistical result is loud and clear," he says. "Planets like our own Earth are out there. Our own Milky Way galaxy is rich in these kinds of planets."

He says that now we're starting to identify such planets, we can go on to study their conditions and chemistry to work out which may be capable of harbouring life like our own. He also estimates from the numbers so far that our own galaxy may contain 100 million habitable planets. He thinks Kepler will be able to confirm discovery of at least 60 of these within the next 2 years.

For the rest of his talk, Sasselov turns to synthetic biology research that he says goes hand in hand with the search for habitable planets. For example, he describes work in the lab of Jack Szostak. Researchers there have been looking at environments that might be found on Earth-like planets, and found that in conditions "with some liquid water and some clays", naturally available molecules can spontaneously form bubbles with cell-like membranes.

"There is immense, powerful potential in life in this universe," Sasselov concludes. "Especially now we know that places like the Earth are common."


Forgotten finds of Tutankhamun's tomb

19. July 2010 10:15

Howard Carter supervises removal of objects from Tutankhamun's tomb. c. Griffith Institute, Oxford

"Our sensations and astonishment are difficult to describe as the better light revealed to us the marvellous collection of treasures: two strange ebony-black effigies of a King, gold sandalled, bearing staff and mace, loomed out from the cloak of darkness; gilded couches in strange forms, lion-headed, Hathor-headed, and beast infernal; exquisitely painted, inlaid, and ornamental caskets; flowers; alabaster vases, some beautifully executed of lotus and papyrus device; strange black shrines with a gilded monster snake appearing from within; quite ordinary looking white chests; finely carved chairs; a golden inlaid throne; a heap of large curious white oviform boxes; beneath our very eyes, on the threshold, a lovely lotiform wishing-cup in translucent alabaster; stools of all shapes and design, of both common and rare materials; and, lastly a confusion of overturned parts of chariots glinting with gold, peering from amongst which was a mannikin. The first impression of which suggested the property-room of an opera of a vanished civilization."

These are the words of archaeologist Howard Carter, describing his first glimpse inside Tutankhamun's tomb after he discovered it in 1922. The treasures within had been undisturbed for 3,300 years.

This discovery is now one of the most famous in all of archaeology - the only intact royal tomb that has ever been found from ancient Egypt. But the details of what Carter found are surprisingly little known. In all, Carter found 5,398 items, so many that it took him 10 years to catalogue them all. Some, like Tut's iconic gold burial mask, are instantly recognisable. But the majority have never been properly studied and published, and are unfamiliar even to experts. Carter died in 1939, just seven years after his excavation ended, and before he could fully publish his findings. The sheer size and importance of his haul seems to have discouraged other scholars from tackling it.

The notes from Carter's excavation, including 3,500 densely-written note cards, more than 1000 photographs taken by Carter's colleague Harry Burton, as well as Carter's diaries and journals, are now held in the Griffith Institute in Oxford. I've just written this article in The Observer about an effort by Jaromir Malek, head of the Griffith Institute, to make all of these materials available online. He and his handful of staff have had to do it in their spare time because no one would fund the project, but after 15 years they have finally finished, and the last pieces will be scanned, transcribed and posted in the next few months.

The result is a really stunning website called Tutankhamun: Anatomy of an Excavation. You can browse the objects from the tomb - some of my favourites include this leopard-skin cloak with golden head and silver claws, this model boat, and this brilliant folding bed. Or you can search for a specific item - type in "mummy" for example (then click on "King's mummy") and you'll find 68 photos of Tut's mummy taken at various stages of the unwrapping process. I also love Burton's eerie photos of the undisturbed tomb.

Malek says he wants to put "moral pressure" on Egyptologists, to encourage them to study this immensely important collection of objects. Researchers still need to study the objects themselves of course, most of which are on display in the Museum of Egyptian Antiquities in Cairo. But the Carter archive includes information that can't be gleaned from looking at the objects today. He recorded exactly where each item was found within the tomb for example. And he saw them in the best possible condition - many of the finds, especially those made of organic material, have decomposed since they were removed from the tomb. Andre Veldmeijer of the PalArch Foundation in Amsterdam used the website in a recent analysis of the footwear found in Tutankhamun's tomb. One pair of leather sandals, delicately embellished with gold leaf and coloured beads, is shown perfectly preserved in Burton's potographs, yet Veldmeijer says his visit to see the shoes in the Cairo museum revealed an oozing black mess. He describes the online archive as "one of the best things in Egyptology".

But the site isn't just for researchers. Malek says he hopes project will bring the forgotten details of the tomb to as many people as possible. "We felt this was important because the discovery is so well-known," he says. "This doesn't belong to Egyptologists only, or even to Egypt only. Everybody should have the right to see what's there."

[Thanks to the Griffith Institute for the above photo, which shows Carter supervising the removal of objects from the tomb in 1922.]


As well as my Observer article mentioned above, which discusses how researchers are now using the archive to make new discoveries about the tomb, you can also listen to my interview with Jaromir Malek on today's Guardian Science Weekly podcast.


Archimedes' flaming steam cannon

15. July 2010 14:49

Archimedes' Mirror by Giulio Parigi

Did Archimedes use mirrors to power steam cannons when fighting against the Romans in the third century BC? That's the suggestion of Italian engineer Cesare Rossi, who has reconstructed how the solar-powered weapon could have worked. The result is ingenious, but historians of ancient technology are sceptical that it bears any relation to anything that Archimedes actually used.

I've just written a story on this for New Scientist, which includes a graphic showing Rossi's suggested design for the cannon. I didn't have room to put much into that story about what other scholars think of the idea, so I've discussed their reactions in a bit more detail below.

 Archimedes is famous for supposedly inventing all kinds of wondrous war machines when the Romans laid siege to Syracuse, Sicily, where he lived. One of the most well-known stories, that he used mirrors to focus sunlight and set fire to enemy ships, seems extremely unlikely, even though modern reconstructions have shown this technique to be theoretically possible.

First, there aren't any sources from Archimedes' own time that tell this story. Sceptics also complain that to keep the sun's rays focused on a moving ship you would need to constantly change the mirror's curvature. And such fires would start very slowly, so those on board would presumably be able to extinguish them.

Rossi believes that another Archimedes legend throws new light on the burning mirror story. Several historical sources, including Petrarch in the 14th century and Leonardo da Vinci in the 15th century, wrote that Archimedes invented a steam-powered cannon, in which pressurised steam at the base of the gun forces a projectile out of the barrel at high speed. And the Greek historian Plutarch (46-120 AD) wrote that during the siege of Syracuse, the Romans saw something that was similar to a pole protruding from the city walls, and ran away shouting: "Archimedes is going to throw something on us now." Rossi says that could be a reference to a cannon.

Several teams have previously looked at whether or not this might work. But Rossi is suggesting a slight twist to the idea. At a conference on Archimedes in Syracuse last month, he suggested that mirrors focusing the sun's rays could have been used to heat the steam cannons. The cannons would then have been used to set fire to ships by hurling hollow projectiles filled with an incendiary fluid, perhaps a mix of sulphur, liquid bitumen, pitch and calcium oxide.

Rossi says this is a much more plausible use of burning mirrors than trying to set fire to distant ships. He points out that mirrors are used today to heat fluid to high temperatures in some applications of solar energy. He calculates that a cannonball measuring 20 centimetres across would have weighed around 6 kilograms and could have been fired from the gun at 60 metres per second, with a range of around 150 metres.

It's all intriguing speculation. But historians are not particularly impressed, mainly because, just as with the burning mirrors, there is no direct mention in the historical record of Archimedes inventing a steam cannon until many centuries after his death. Tracey Rihll, an expert in ancient science and technology from the University of Swansea, calls Rossi's idea an "interesting hunch" but says that to make a convincing case, Rossi would need to explain how writers such as da Vinci could have found out about Archimedes' invention. "Leonardo did have access to ancient texts," she says. "There is a paper about his thoughts on colour being directly influenced by the rediscovery of Aristotle's On Colours, for example. But a case needs to be made for something similar here."

Rihll also points out that many of the details that Rossi uses in his calculations are very different from the ones described by da Vinci. For example, da Vinci described a 25 kg solid iron ball, whereas Rossi considers a 6 kg ball made of hollow clay.

Another expert, Serafina Cuomo at Birkbeck College, University of London, has similar concerns. Reconstructions demonstrate a "technological possibility" she says, but don't constitute historical evidence: "We have a perfectly good explanation for later accounts that attribute steam cannons to Archimedes, and that is that Archimedes became a quasi-mythical icon of the scientist capable of constructing incredible weapons, and that in later medieval times some new weapons, ie cannons, did come onto the scene. Put the two together, and you have the story." Rihll agrees: "Archimedes' name attracts inventions to itself like moths to a flame." 

Rossi admits that showing how the steam cannon could have worked "doesn't mean that it happened". But he adds that it is a much more likely use of burning mirrors than setting fire to ships directly. He doesn't have the funds to build a working model of the solar-powered cannon, but says that if anyone is interested, he can provide the technical drawings. 

So, whether or not Rossi is right about the steam cannon, what other impressive weapons might Archimedes have employed against the Romans? The Greeks were certainly handy with a catapult. "Those of Archimedes' time could outperform [Rossi's steam cannon] in every department: payload weight, range, ease of use, reliability, health and safety," says Rihll. The idea that Archimedes invented a giant claw with which to attack ships is also plausible - Rihll believes that this is the most likely explanation of the pole-like device described by Plutarch. According to Cuomo, the closest invention to a steam cannon in ancient sources is a mention of a compressed air-operated catapult in Philo of Byzantium.


Circles around Stonehenge

6. July 2010 09:43

Stonehenge in Wiltshire, UK c. Wikimedia Commons

One interesting trend to watch in archaeology is the use of computers to simulate how the past would have looked. I've blogged before about a reconstruction that allows you to take a virtual walk through ancient Rome, and a project to digitally simulate authentic lighting conditions for ancient scenes and buildings.

Now similar technology is being applied to Stonehenge - not so much the famous standing stones themselves, but other monuments and burial mounds in the area. Researchers have long speculated over whether burial monuments from the Early Bronze Age were positioned according to particular geometric patterns, perhaps in a way that reflected the cosmology or belief system of the time. For example, Ann Woodward of the University of Birmingham's Institute of Archaeology and Antiquity has suggested that monuments around Stonehenge seem to be arranged in two roughly concentric circles centred on the standing stones, one with a radius of 0.6-1.2 kilometres, and one with a radius of 2-2.4 kilometres. Such ideas are quite tricky to test, however, especially when you have remains of a variety of different ages and types, positioned on a rolling three-dimensional landscape. So Woodward's colleague Vince Gaffney is leading a 3-year effort to map buried archaeological remains in the terrain around Stonehenge with the latest geophysical imaging techniques.

The Stonehenge Hidden Landscapes Project, which starts this week, will involve taking millions of measurements of the position of remains in the ground. These will be analysed using computer software originally developed for building video games, to produce 2D and 3D images of how the landscape would have looked in Neolithic times. Then researchers can use the reconstructions to test their ideas about how different monuments and burial mounds were arranged.


That Tut conspiracy

5. July 2010 22:39

Tutankhamun's inner mummy case replica c. HoremWeb

I've just had a first-hand - and rather disconcerting - insight into how conspiracy theories start. A week or so ago I wrote a light-hearted blog post for New Scientist, looking into a theory that King Tutankhamen might have had a hormonal disorder that among other things causes underdeveloped genitalia.

Researchers analysing Tut's mummy had just ruled out the idea, citing the fact that Tut's penis is "well-developed". Intriguingly, however, their paper said that the penis is no longer attached to the rest of the mummy. On a whim I decided to double check that the organ is definitely Tut's and couldn't have been swapped by ancient embalmers to cover up his condition. Unlikely, perhaps, but surely a question that was begging to be asked.

Egyptologist John Taylor confirmed that the penis is indeed Tut's, as it was attached to the body when the mummy was first unwrapped. It must have broken off in modern times, probably during an early autopsy. So far so interesting - but it was clear that nothing untoward had occurred. I added a couple of tongue-in-cheek digs at conspiracy theorists, and it made a fun little tale for a Friday afternoon.

Unfortunately, some journalists seem to have taken those digs seriously. The story went viral. But it wasn't my story that went viral. In the version rapidly gaining momentum across the internet, I was now reported as claiming that Tut's penis has been stolen in order to cover up its small size.

My original article ruled out the idea that ancient embalmers swapped Tut's penis. And though I mentioned in passing the well-known fact that it was thought missing for a while, I did not suggest that the penis has been switched more recently either - I'm not aware of any evidence for this idea.

The trouble seems to have started with an article on Time's website, written by an intern, who reported that "some, including Marchant...believe that Tut's penis was swapped sometime after his body was embalmed, suggesting a conspiracy to save him from embarrassment". (The words "including Marchant" have since been removed, at my request.)

Other blogs and news sites followed, twisting the story further. According to the New York Daily News, "scientists" think the penis was taken. Meanwhile a Denver blog reports that the penis is still missing.

This reminds me a bit of a news story I once edited for New Scientist, about a physicist who said he didn't think the elusive Higgs boson (nicknamed "the God particle") would ever be found. The news story and accompanying editorial reported that other physicists were confident the particle would be found, explained why the £6-billion Large Hadron Collider (LHC), then being built to look for the Higgs, was still important, and pointed out that it would actually be more exciting for physics if the Higgs particle didn't exist.

Then The Times newspaper followed up the story under the headline "God particle disappears down £6-billion drain", and New Scientist received sackfuls of complaints from physicists around the world. It was the Times headline that really upset them, but they blamed New Scientist. No matter how responsible our own story, they said, we were irresponsible to provide ammunition that might allow others to attack the LHC.

With the Tut blog post, was I irresponsible for writing something that others could then twist into a conspiracy theory? With hindsight I wish I'd spent more time making sure the article was idiot-proof, though I'd hate to think that journalists can't have fun with stories, for fear of how they might be misconstrued. Either way, I haven't had any angry letters from Egyptologists yet (though one blogger has accused me of "living in the realm of fantasy"). But I've got some sacks ready just in case...


Cleopatra and the eclipse

26. June 2010 08:56

Solar eclipse

Here's the update I promised in my post on the Dendera Zodiac. If you remember, the zodiac is an ancient Egyptian bas-relief carved onto huge sandstone blocks. It originally formed part of the ceiling of a temple in Dendera, Egypt, but is now on display in the Louvre in Paris.

The design is a representation of the sky. Egyptologist Sylvie Cauville and astrophysicist Eric Aubourg used the positions of the star constellations and planets to date the Zodiac to between 15 June and 15 August in the year 50 BC, during the period between the death of Cleopatra's father, Ptolemy Auletes, in 51 BC, and the establishment of joint rule between Cleopatra and Caesarion (her 5-year-old son by Julius Caesar), in 42 BC.

Two eclipses - the solar eclipse of 7 March 51 and the lunar eclipse of 25 September 52 - are represented on the skyscape in the locations where they would have occurred.

But why would the Egyptians have wanted to commemorate this particular moment? I emailed Cauville and she says her hypothesis is that the total solar eclipse coincided in Alexandria with the death of Cleopatra's father. "She [Cleopatra] may have wanted to inscribe for eternity the passing of power from King-Rê to herself, the female sun."

I'm so glad I asked! Rê is another name for the sun god, Ra, by the way. The pharaohs, including those of Cleopatra's dynasty, often claimed that they were sons and daughters of Ra.

Dendera would have been chosen because the temple there was dedicated to female royalty. (The temple at Edfu, where two similar zodiacs are located, is dedicated to the male royalty.) The Dendera zodiac was on the ceiling of one of the temple's two chapels dedicated to Osiris, the god of eternal return. There's more about all this in Cauville's 1997 book, Le Zodiaque d'Osiris.

"It's a shame that so many fanciful things have been written about the Zodiac," adds Cauville. "The astronomical reality is so much more beautiful." Couldn't agree more.

[Cauville's comments have been translated from French]


King Tut - and his penis

25. June 2010 18:06

Tutankhamun innermost coffin

I've had fun today looking into the latest arguments over the mummy of Tutankhamun. The pharaoh died young, aged around 19, so there's been plenty of speculation over what killed him since his mummy was first unwrapped in 1922.

Murder - by a blow to the back of the head or by poison - has been suggested. And signs of broken leg led to the idea that he fell from his chariot during a hunting accident.

Egypt's chief archaeologist Zahi Hawass and colleagues recently carried out an extensive scientific investigation of Tut's mummy as well as several others from his family (all captured on film of course for an accompanying TV documentary). They reported in JAMA earlier this year that he probably died from a debilitating bone disorder, combined with an attack of malaria.

But a letter just published in JAMA suggests that sickle cell disease is a more likely explanation. You can read more about this in this news story I've written for New Scientist today.

This letter was just one of several comments published this week on Hawass's work. One of them urges caution over the DNA results from the mummies, suggesting that contamination could have crept in. Another challenges the identification of mummy KV55 as Akhenaten, Tut's father.

But the letter that I was most intrigued by suggests that Tutankhamun and family, including Akhenaten, may have suffered from a hormonal disorder that given them elongated skulls, and caused the men to develop breasts. This would explain why artwork of the time depicts Tutankhamun, Akhenaten and others with long heads and feminine figures (just type "Akhenaten" into a Google image search and you'll see what I mean).

A key piece of evidence in this debate is King Tut's penis, which it turns out has been broken away from his body. It's also impossible to check whether Tut had breasts, because the front of his chest is missing. Is this a cover-up? You can read more on what I found out in a blog post here...


Mystery of an ancient zodiac

24. June 2010 10:22

The Zodiac of Dendera at the Louvre Museum

Embedded in the ceiling of a small room in the Egyptian antiquities section of the Louvre, Paris, are two huge sandstone blocks. Cut into them is a dramatic circular pattern of figures and hieroglyphs - the Dendera zodiac.

I've reviewed a book about this fascinating bas-relief in today's New Scientist. The Zodiac of Paris, by historian Jed Buchwald and writing professor Diane Greco Josefowicz, discusses the stormy debate triggered when the zodiac was first discovered in 1790 by French scientists attached to Napoleon's campaign in Egypt.

The zodiac's original home was the ceiling of an ancient temple near the village of Dendera, on the west bank of the Nile. It was taken to France in 1821 by engineer Jean Lelorrain - the book has a vivid description of his epic if politically incorrect expedition. He used gunpowder to blast the blocks from their original home, before using a sledge on rollers to drag them to the Nile (it took 16 days to cover the 4 miles). The river was at its lowest ebb so he also had to build a 60-foot earth ramp to slide the stones down to the water's edge, not to mention the fact that the boat he was trying to load them onto nearly sank under the weight.

The book focuses, however, on efforts of scientists and intellectuals of the time to date the zodiac. Scientists believed that the zodiac, along with three others found - one more at Dendera and two at Esneh - was intended to represent the state of the sky when it was produced. By deciphering the symbols, therefore, they could match up the zodiac to a particular date and work out how old the temple was. Each scholar seemed to have his own method of interpreting the symbols but most believed they were thousands of years old, perhaps dating to as far back as 15,000 BC.

All this went down extremely badly with religious conservatives, as according to the Bible the world itself was only six thousand years old, and humanity had been all but destroyed in a catastrophic flood in around 2000 BC. As the book's blurb says, the resulting row wasn't just about the zodiac, but "the merits of scientific calculation as a source of knowledge about the past". With today's arguments over intelligent design, it's a useful reminder that clashes between scientists and religious fundamentalists over the validity of different sources of knowledge are nothing new.

The book ends with the young Egyptologist Jean-Francois Champollion, best known for deciphering hieroglypics, who concluded in the early 19th century that the astronomical symbols in the zodiac formed part of a text, not an image of a sky, and dated it (much less controversially) to Roman times.

What really interests me about the zodiac, however, is what we know now about how old it is, and what the design represents - something that Buchwald and Josefowicz don't address. So I dug around a little bit and the latest interpretation is that it dates from around 50 BC. The key is an empty cartouche on a part of the temple's ceiling that was left in Egypt. A cartouche is a hieroglyph that looks like a little box and usually it would contain the name of the current ruler. Because it's empty, historians think the temple was built during the gap between death of Cleopatra's father, Ptolemy Auletes, in 51 BC, and the establishment of joint rule between Cleopatra and Caesarion (her 5-year-old son by Julius Caesar), in 42 BC.

Sylvie Cauville of the Centre for Computer-aided Egyptological Research (CCER) based at Utrecht University is the latest scholar to tackle the zodiac itself. She believes that does represent a map of the sky after all.

According to the summary on the Louvre website: "The vault of heaven is represented by a disc, held up by four women assisted by falcon-headed spirits. Thirty-six spirits or "decans" around the circumference symbolise the 360 days of the Egyptian year. The constellations shown inside the circle include the signs of the zodiac, most of which are represented almost as they are today. Aries, Taurus, Scorpion and Capricorn, for example, are easily recognisable, whereas others correspond to a more Egyptian iconography: Aquarius is represented as Hapy, the god of the Nile flood, pouring water from two vases."

Cauville has identified the symbols for the five planets known at the time, and says they are located on the map within certain signs of the zodiac. For example Venus is behind Aquarius, Jupiter is near Cancer, Mars is directly above Capricorn. This particular configuration of the planets among the constellations only happens about once every thousand years, and it occurred between 15 June and 15 August in the year 50 BC - matching perfectly the date suggested by the empty cartouche.

One lovely detail is that the map shows two eclipses, in the part of the sky where they would have been seen. Again from the Louvre website: "The solar eclipse of 7 March 51 is depicted as the goddess Isis holding a baboon (the god Thoth) by its tail, signifying her attempt to stop the moon from hiding the sun. The lunar eclipse of 25 September 52 is represented by an udjat-eye (the "whole one") because a lunar eclipse only occurs when the moon is full."

I'm still intrigued by why the Egyptians would have wanted to represent the sky at this particular point in time. The chapel that originally held the the bas-relief was intended to celebrate the resurrection of the god Osiris, so perhaps that's a clue. If I find out I'll post again...


See my follow-up post on this here.