The backyard volcano

Of all of the sciences, geology is the one where deep understanding of the underlying processes eluded us the longest.  Even the two other contenders -- genetics and astronomy -- were at least partially unraveled sooner.  Plate tectonics, the model that provides a framework for comprehending just about every other geological process, wasn't elucidated until Frederick Vine, Drummond Matthews, and Harry Hess came along in the early 1960s.  Until then, geology texts fell back on hand-waving explanations like synclines and anticlines, and pretty much ignored questions like why most of the world's volcanoes and major earthquakes fall along a tracery of curves that encircle the Earth like the stitching on a baseball (the most famous of which is the Pacific Ring of Fire).

Part of the reason it took us so long to figure all this out is because geological processes are, for the most part, slow, so it's easy to look around and conclude that the Earth has pretty much always looked like it does today.  Then... they discovered anomalies like marine fossils in the Himalayas, Kansas, the Rockies, and right here in my own neck of the woods in upstate New York.  It took the brilliant Scottish geologist Charles Lyell to recognize that if rates of sedimentation are fairly constant, then big sedimentary rock layers like the White Cliffs of Dover must have taken tens of millions, rather than thousands, of years to form.  The recognition of how slow most geological phenomena were meant the Earth was a great deal older than the six-thousand-year estimate by Archbishop Ussher -- setting up the first of many clashes between geologists and the church establishment.

But "usually slow" doesn't mean "always slow."  Sometimes major geological processes can occur, literally, overnight.  Take, for example, the appearance in 1943 of a new volcano, dubbed Parícutin after the nearest town, in a Mexican farmer's cornfield.

The locals did at least have a little bit of warning.  For weeks prior to the initial eruption, they had heard sounds "like thunder but with no clouds in the sky," now thought to be the rumblings of magma moving beneath the surface.  There were over twenty small earthquakes over 3.2 on the Richter Scale, and hundreds of smaller ones -- the day before the eruption, there were more than three hundred small earthquakes.

What happened next is best said in the words of Dionisio Pulido, the farmer who witnessed it first-hand:

At 4 p.m., I left my wife to set fire to a pile of branches when I noticed that a crack, which was situated on one of the knolls of my farm, had opened... and I saw that it was a kind of fissure that had a depth of only half a meter.  I set about to ignite the branches again when I felt a thunder, the trees trembled, and I turned to speak to Paula; and it was then I saw how, in the hole, the ground swelled and raised itself two or two and a half meters high, and a kind of smoke or fine dust – grey, like ashes – began to rise up in a portion of the crack that I had not previously seen...  Immediately more smoke began to rise with a hiss or whistle, loud and continuous; and there was a smell of sulfur.

By the next morning, where Pulido's cornfield had been was a scoria cone fifty meters high; a week later, it was double that.  It was continuously erupting volcanic bombs and small pyroclastic flows, and Pulido decided that his home and land were done for, so he got the hell out.  Before leaving, he put up a sign saying "This volcano is owned and operated by Dionisio Pulido" -- indicating that even in dire circumstances, you can still hang on to your sense of humor.

Parícutin in 1943 [Image is in the Public Domain]

The entire eruption cycle went on for two years, and by the end, there was a massive conical mountain, over four hundred meters tall, where before there'd only been a flat valley.  Only three people died during the eruption, and oddly, none of them were from the lava or pyroclastic surges; the three died when they were struck by lightning during an ash eruption.  (The tiny particles of volcanic ash are often electrically charged; lightning strikes in ash columns are common.)

It did, however, render much of the (former) valley uninhabitable.  Here's a photograph of the ruins of the old church of San Juan Parangaricutiro, which was destroyed by lava and ash along with the rest of the village of the same name:

[Image is in the Public Domain]

At the time of the eruption, all that was known was that it added another peak to the Trans-Mexican Volcanic Belt, which runs east-west across the entire country and includes much more famous volcanoes such as Popocatépetl.  Since then, we've learned that the whole range owes its existence to the subduction of the Rivera and Cocos Plates underneath the North American Plate at the Middle America Trench; the waterlogged rock and sediments are pulled down into the upper mantle, heated, and melt, forming the magma that eventually erupts somewhere behind the trench.

But at the time, the appearance of a volcano was a source of mystification both to the locals and the scientists.  To be sure, some geological phenomena are sudden; earthquakes, for example, often happen without much in the way of warning (and accurate earthquake prediction is still a dicey affair).  But we're used to things pretty much staying in the shapes and positions they were in before.  It takes a huge earthquake -- the 9.2-magnitude Anchorage megathrust quake comes to mind -- to radically reshape the land, in this case raising a long stretch of coastline by as much as nine meters.  And while big volcanic eruptions, such as the current one from Mount Etna, are spectacular and can be deadly, most of the time they're from volcanoes we already knew about.

Parícutin, though, kind of came out of nowhere, at least by the scientific understanding of the time.  And that's one of the benefits of science, isn't it?  It allows us to understand the processes involved, not just name them after they've happened.  While we're still not at the point where we can predict with much lead time when something like this will happen, at least now we can say with some assurance that we understand why it happened where it did.

Little consolation to Dionisio Pulido, of course.  I'm guessing that "owning and operating" a volcano was nowhere near as lucrative as his cornfield had been.  But that's life in a geologically active area.  However much we understand about the science behind such events, it's good to keep in mind there's always a human cost.

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Analysis of a monster

In my post a couple of days ago about the unstable geology of the Greek island of Thera, I stated that this is far from the only place in the world where lots of people live in harm's way from the vagaries of plate tectonics.  I mentioned the Cascadia Subduction Zone, off the coast of the Pacific Northwest, and included a link to the rather desultory post I'd made a while back about what's going on over there.  A loyal reader of Skeptophilia wondered if I might write a more thorough piece about the terrifying situation looming in that beautiful part of the world, so here I am to elaborate, and probably to scare the absolute shit out of anyone living in coastal British Columbia, Washington, Oregon, and northern California.

Even after the general acceptance of plate tectonics by geologists in the 1960s and 1970s, it took a long time for them to see what was happening in the northeastern Pacific.  The presence of a ridge (divergent zone) meant that the seafloor was spreading on both sides; the fact that the small Explorer, Juan de Fuca, and Gorda Plates were being shoved eastward meant that there had to be a trench somewhere between the ridge and continental North America.  But the earliest sounding techniques couldn't find one.  It turned out that it was buried -- submerged under hundreds of meters of muck, silt and sand washed out of the region's numerous rivers.

This, and the fact that there hadn't been a big earthquake in the Northwest since settlement by people of European descent, led a lot of geologists to the conclusion that the trench was "aseismic."  Either the small plates east of the ridge weren't moving, or they were slipping underneath the North American Plate so smoothly that there were no measurable earthquakes.

This wasn't just a little bit wrong.  This was stunningly wrong.  This was wrong with whipped cream and a cherry on top.

The red dots represent earthquakes within the seafloor; the green dots are earthquakes within the continental crust of North America.  [Image is in the Public Domain courtesy of the United States Geological Survey]

The Explorer, Juan de Fuca, and Gorda Ridges are very much active spreading centers, and the fact that there haven't been any recent big earthquakes along the trench -- the Cascadia Subduction Zone, denoted on the map by the line with black triangles -- is not good news.  The entire coastline of the Pacific Northwest is compressing as the three small plates get shoved under North America, just like trying to slide something underneath a throw rug makes it rumple and hump up.  In fact, surveys measuring the positions of the peaks in the Cascade Range and on Vancouver Island have found that the whole terrain is being squished west-to-east, so entire mountains are being pushed toward each other.

Imagine the power required to do that.

Further, the fact that the trench is filled with mud doesn't mean the subduction zone is aseismic; quite the opposite.  It turns out that a large part of the mud deposits there are turbidites -- the result of colossal underwater landslides.

Such as might occur during an enormous earthquake.

More of the mechanism was elucidated in 2003, when researchers found that the whole region was experiencing a phenomenon called episodic tremor and slip, where deeper parts of the conjoined plates -- the bits that are hotter and more plastic -- slip against each other, causing barely a rumble.  This slip/tremor happens like clockwork every fourteen months.  While this may sound like a good thing, it's actually the opposite.  Releasing stress that has built up in the deep parts of the fault merely passes that stress upward to the colder, shallower parts that are still locked together, each ETS episode dialing up the energy like the clicking of another tooth in a ratchet.

So along the subduction zone, the two opposing sides of the plates are stuck together, building up more and more tension -- tension that will one day be released as the faultline unzips, and the whole northwest coast of the continent springs back toward the west.

To say the result will be catastrophic is understatement of the year.

It's happened before.  In fact, geologists taking cores of the aforementioned turbidite sediments off the coast of Washington found evidence that in the past ten thousand years it's happened nineteen times.  The spacing between megathrust earthquakes -- as these are called -- varies between three hundred and nine hundred years, with the average being around five.  And the last one happened a little over 323 years ago.

We actually know down to the hour when it happened -- about 9 PM local time, January 26, 1700.  Indigenous tribes in the area have a long tradition that many years ago, there was a terrible earthquake one midwinter night, during which the seashore dropped and salt water flooded in, killing many people.  Evidence from tree rings in "ghost forests" -- the trunks of hundreds of western red cedars that had all been killed simultaneously by an influx of salt -- showed that some time in the 1690s or early 1700s there had been a massive flood from the ocean as the coastline suddenly dropped by several meters.  The exact date was determined from records across the Pacific, where Japanese scribes describe what they called an "orphan tsunami" (a huge wave that, from their perspective at least, was not preceded by an earthquake) striking coastal Japan.  Knowing the speed with which such waves travel across the ocean, geologists were able to determine exactly when the fault last unzipped from end to end.

The earthquake that resulted is estimated to have been somewhere between 8.7 and 9.2 on the Richter Scale, and to have resulted in land movement averaging around twenty meters.

Not pleasant to consider how that would play out if it happened today.

The worst part, for coastal communities today, is how close the Cascadia Subduction Zone is to shore.  At its closest approaches -- near the west coast of Vancouver Island, and from central Oregon south to Cape Mendocino -- it's estimated that the lag time between the ground shaking and the first of the tsunami waves striking the shore will be around eight minutes.  That's eight minutes between being thrown all over the place by an enormous earthquake, and somehow getting yourself to high ground before you're hit by a giant wall of salt water.

I remember when I first heard in detail about the dangers of the Cascadia Subduction Zone -- in 2015, from Kathryn Schulz's brilliant analysis in The New Yorker called "The Really Big One."  It impressed me so much I actually used the fault as a plot point in my novel In the Midst of Lions, where the story is bracketed by earthquakes (one of them massive).  But when I was a Seattle resident in the 1980s, I had no idea.  I still dearly love the Northwest; not only does it have the ideal climate for a fanatical gardener like myself, it has amazing spots for hiking and camping.  During my time there I spent many happy days on the coast of the Olympic Peninsula -- never realizing that a monster lurked offshore.

So while I miss many things about the Northwest, I know I could never live there again.

It may be that the fault won't rupture for another two hundred years; on the other hand, it could happen tomorrow.  While our ability to analyze plate tectonics is light years beyond what it was even thirty years ago, when the situation in the Northwest first began to come clear, we still don't have any way to determine when the earthquake will happen with any kind of precision.  At the moment, all we know is that it will rupture, sooner or later.

And I don't want to be anywhere near it when it does.

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Big geology

It's easy to get overwhelmed when you start looking into geology.

Both the size scale and the time scale are so immense that it's hard to wrap your brain around them.  Huge forces at work, that have been at work for billions of years -- and will continue to work for another billion.  Makes me feel awfully... insignificant.

The topic comes up because of three recent bits of research into just how powerful geological processes can be.  In the first, scientists were studying a crater field in Wyoming that dates to the Permian Period, around 280 million years ago (28 million years, give or take, before the biggest mass extinction the Earth has ever experienced).  The craters are between ten and seventy meters in diameter, and there are several dozen of them, all dating from right around the same time.  The thought was that they were created when an asteroid exploded in the upper atmosphere, raining debris of various sizes on the impact site.

The recent research, though, shows that what happened was even more dramatic.

"Many of the craters are clustered in groups and are aligned along rays," said Thomas Kenkmann of the University of Freiburg, who led the project.  "Furthermore, several craters are elliptical, allowing the reconstruction of the incoming paths of the impactors.  The reconstructed trajectories have a radial pattern.  The trajectories indicate a single source and show that the craters were formed by ejected blocks from a large primary crater."

So what appears to have happened is this.

A large meteorite hit the Earth -- triangulating from the pattern of impact craters, something like 150 and 200 kilometers away -- and the blast flung pieces of rock (both from the meteorite and from the impact site) into the air, which then arced back down and struck at speeds estimated to be up to a thousand meters per second.  The craters were formed by impacts from rocks between four and eight meters across, and the primary impact crater (which has not been found, but is thought to be buried under sediments somewhere near the Wyoming-Nebraska border) is thought to be fifty kilometers or more across.

Imagine it.  A huge rock from space hits a spot two hundred kilometers from where you are, and five minutes later you're bombarded by boulders traveling at a kilometer per second. 

This is called "having a bad day."

[Image licensed under the Creative Commons State Farm, Asteroid falling to Earth, CC BY 2.0]

The second link was to research about the geology of Japan -- second only to Indonesia as one of the most dangerously active tectonic regions on Earth -- which showed the presence of a pluton (a large underground blob of rock different from the rocks that surround it) that sits right near the Nankai Subduction Zone.  This pluton is so large that it actually deforms the crust -- causing the bit above it to bulge and the bit below it to sag.  This creates cracks down which groundwater can seep.

And groundwater acts as a lubricant.  So this blob of rock is, apparently, acting as a focal point for enormous earthquakes.

The Kumano pluton (the red bulge in the middle of the image).  The Nankai Subduction Zone is immediately to the left.

Slipping in this subduction zone caused two earthquakes of above magnitude 8, in 1944 and 1946.  Understanding the structure of this complex region might help predict when and where the next one will come.

If that doesn't make you feel small enough, the third piece of research was into the Missoula Megaflood -- a tremendous flood (thus the name) that occurred 18,000 years ago.

During the last ice age, a glacial ice dam formed across what is now the northern Idaho Rockies.  As the climate warmed, the ice melted, and the water backed up into an enormous lake -- called Lake Missoula -- that covered a good bit of what is now western Montana.  Further warming eventually caused the ice dam to collapse, and all that water drained out, sweeping across what is now eastern Washington, and literally scouring the place down to bedrock.  You can still see the effects today; the area is called the "Channeled Scablands," and is formed of teardrop-shaped pockets of relatively intact topsoil surrounded by gullies floored with bare rock.  (If you've ever seen what a shallow stream does to a sandy beach as it flows into sea, you can picture exactly what it looks like.)

The recent research has made the story even more interesting.  One thing that a lot of laypeople have never heard of is the concept of isostasy -- that the tectonic plates, the chunks of the Earth's crust, are actually floating in the liquid mantle beneath them, and the level they float is dependent upon how heavy they are, just as putting heavy weights in a boat make it float lower in the water.  Well, as the Cordilleran Ice Sheet melted, that weight was removed, and the flat piece of crust underneath it tilted upward on the eastern edge.

It's like having a full bowl of water on a table, and lifting one end of the table.  The bowl will dump over, spilling out the water, and it will flow downhill and run off the edge -- just as Lake Missoula did.

Interestingly, exactly the same thing is going on right now underneath Great Britain.  During the last ice age, Scotland was completely glaciated; southern England was not.  The melting of those glaciers has resulted in isostatic rebound, lifting the northern edge of the island by ten centimeters per century.  At the same time, the tilt is pushing southern England downward, and it's sinking, at about five centimeters per century.  (Fortunately, there's no giant lake waiting to spill across the country.)

We humans get a bit cocky at times, don't we?  We're powerful, masters of the planet.  Well... not really.  We're dwarfed by structures and processes we're only beginning to understand.  Probably a good thing, that.  Arrogance never did anyone any favors.  There's nothing wrong with finding out we're not invincible -- and that there are a lot of things out there way, way bigger than we are, that don't give a rat's ass for our little concerns.

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People made fun of Donald Rumsfeld for his statement that there are "known unknowns" -- things we know we don't know -- but a far larger number of "unknown unknowns," which are all the things we aren't even aware that we don't know.

While he certainly could have phrased it a little more clearly, and understand that I'm not in any way defending Donald Rumsfeld's other actions and statements, he certainly was right in this case.  It's profoundly humbling to find out how much we don't know, even about subjects about which we consider ourselves experts.  One of the most important things we need to do is to keep in mind not only that we might have things wrong, and that additional evidence may completely overturn what we thought we knew -- and more, that there are some things so far out of our ken that we may not even know they exist.

These ideas -- the perimeter of human knowledge, and the importance of being able to learn, relearn, change directions, and accept new information -- are the topic of psychologist Adam Grant's book Think Again: The Power of Knowing What You Don't Know.  In it, he explores not only how we are all riding around with blinders on, but how to take steps toward removing them, starting with not surrounding yourself with an echo chamber of like-minded people who might not even recognize that they have things wrong.  We should hold our own beliefs up to the light of scrutiny.  As Grant puts it, we should approach issues like scientists looking for the truth, not like a campaigning politician trying to convince an audience.

It's a book that challenges us to move past our stance of "clearly I'm right about this" to the more reasoned approach of "let me see if the evidence supports this."  In this era of media spin, fake news, and propaganda, it's a critical message -- and Think Again should be on everyone's to-read list.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]

Forecasting on a fault line

Living in an earthquake zone is risky business.

I lived for ten years in Seattle, which is immediately adjacent to the Cascadia Subduction Zone, widely considered to be one of the most potentially dangerous faults in the world.  The little Juan de Fuca plate -- all that's left of a much larger piece of oceanic crust that once lay underneath Panthalassa, the ocean that surrounded the supercontinent Pangaea back around the time of the Permian-Triassic Extinction of 251 million years ago -- is slowly disappearing as it gets pulled underneath the North American Plate by convection currents in the mantle.  Subduction zone earthquakes occur along trenches that form the boundaries between plates that are moving toward each other, generating a "thrust fault" as one plate dives beneath the other.  Not only do these produce some of the most massive earthquakes known, they also generate volcanoes like Mount Saint Helens and Mount Rainier.

So lovely as the Seattle area is, it's kind of a disaster waiting to happen.  If you have a high tolerance for being freaked out by the power of the natural world, or you don't live in the Pacific Northwest (or both), you should read journalist Kathryn Schulz's wonderful analysis "The Really Big One" that appeared in The New Yorker in 2015.  Her predictions for what will happen to the area when Cascadia ruptures are truly terrifying -- and would be enough to keep me from ever moving back there, much as I loved western Washington for its culture, climate, and natural beauty.

[Image is in the Public Domain]

If you read the article hoping that Schulz (or the geologists she interviewed) can tell you when the "Really Big One" is going to occur, you're not going to find what you're looking for.  We have a pretty good idea of where earthquakes occur and the types of faults that cause them, but predicting when they'll happen is far more problematic.  And sometimes, even the "where" isn't predictable.  In November of 2019 a 5.0 magnitude quake hit the Rhône Valley in France, along the La Rouvière Fault -- a fault zone that we thought was last active twenty million years ago.

Just last week, though, three papers came out looking at the warning signs that a fault is about to rupture, and methods we may be able to use to predict when they'll happen and how big they'll be.  Getting better at this is imperative for the millions of people who live in quake-prone areas, and could potentially save countless lives.

The first, in the journal Nature, was by a team led by Jonathan Bedford of Helmholtz Centre Potsdam.  In "Months-Long Thousand-Kilometre-Scale Wobbling Before Great Subduction Earthquakes," we learn that there are warning signs -- a slow backward drag on the plate margin that ends with a massive slip in the opposite direction, a little like pulling backward on a bowstring and then letting go suddenly.  The authors write:

[We used] a recently developed trajectory modelling approach that is designed to isolate secular tectonic motions from the daily GNSS time series to show that the 2010 Maule, Chile (moment magnitude 8.8) and 2011 Tohoku-oki, Japan (moment magnitude 9.0) earthquakes were preceded by reversals of 4–8 millimetres in surface displacement that lasted several months and spanned thousands of kilometres.  Modelling of the surface displacement reversal that occurred before the Tohoku-oki earthquake suggests an initial slow slip followed by a sudden pulldown of the Philippine Sea slab so rapid that it caused a viscoelastic rebound across the whole of Japan.

The second paper, in Science, looked at what's happening deep underground beneath one of the most famous fault zones, the strike-slip San Andreas Fault.  In "Excitation of San Andreas Tremors by Thermal Instabilities Below the Seismogenic Zone," geologists Lifeng Wang of the China Earthquake Administration and Sylvain Barbot of the University of Southern California found that temperature patterns can predict the likelihood of a fault suddenly giving way.  For a while, the pieces of the plate margin can slowly, steadily grind past each other, but that motion generates frictional heating.  This can lead to rapid fault failure as the warming rock becomes more plastic.  "Just like rubbing our hands together in cold weather to heat them up, faults heat up when they slide. The fault movements can be caused by large changes in temperature," said study co-author Sylvain Barbot, in an interview with Science Daily.  "This can create a positive feedback that makes them slide even faster, eventually generating an earthquake."

Last, in Nature Communications, geologists Claudia Hulbert and Romain Jolivet (of the École Normale Superieure) and Bertrand Rouet-LeDuc and Paul Johnson (of the Geophysics Group at Los Alamos National Laboratory) turned the power of machine learning on past patterns of seismic instability, and found that large "megathrust" earthquakes were preceded by as much as a year-long slow slip.  Where this slip is occurring, and how fast, might give us advance warning of a major fault rupture:

Slow slip events result from the spontaneous weakening of the subduction megathrust and bear strong resemblance to earthquakes, only slower.  This resemblance allows us to study fundamental aspects of nucleation that remain elusive for classic, fast earthquakes.  We rely on machine learning algorithms to infer slow slip timing from statistics of seismic waveforms.  We find that patterns in seismic power follow the 14-month slow slip cycle in Cascadia, arguing in favor of the predictability of slow slip rupture.  Here, we show that seismic power exponentially increases as the slowly slipping portion of the subduction zone approaches failure, a behavior that shares a striking similarity with the increase in acoustic power observed prior to laboratory slow slip events.  Our results suggest that the nucleation phase of Cascadia slow slip events may last from several weeks up to several months.

Even though such a pattern of slow slips might tell us that a major earthquake is imminent, it's unlikely we'll ever be able to say "... and it's going to happen next Friday at ten A.M."  And given our penchant for ignoring science unless it can give us pinpoint accuracy, we're probably not going to see much change in our behavior.  After all, that tendency is at the heart of the United States's failure to address the COVID-19 pandemic -- the scientists were saying back in December and January, "this has the capacity to be deadly and fast-spreading," and government officials said, "How fast and how deadly?"  The scientists had to say, "We're not sure yet," and that was insufficient for leaders to take swift and decisive action.  (And that's not even taking into consideration that Donald Trump knew about the danger, admitted up front the potential devastation COVID-19 could cause, and deliberately decided to lie about it because he was afraid it would hurt his chances of being re-elected.)

So we're not so good at reacting to clear and present dangers if the remedy is inconvenient or costly.  As James Burke said, in his frighteningly prescient 1991 documentary After the Warming, "The scientists said that devastating climate change was going to happen at some point, but for most people that wasn't good enough.  We wouldn't pay for what amounts to climate insurance, even though we happily insure our lives and our property against far less likely occurrences."

Be that as it may, I'm glad we're seeing this progress being made.  Earthquakes are notorious amongst natural disasters at giving no warning whatsoever, so anything we could do to figure out how to predict them more accurately could potentially save lives.

But even so, I don't think I'd want to live in the Pacific Northwest again.

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Humans have always looked up to the skies.  Art from millennia ago record the positions of the stars and planets -- and one-off astronomical events like comets, eclipses, and supernovas.

And our livelihoods were once tied to those observations.  Calendars based on star positions gave the ancient Egyptians the knowledge of when to expect the Nile River to flood, allowing them to prepare to utilize every drop of that precious water in a climate where rain was rare indeed.  When to plant, when to harvest, when to start storing food -- all were directed from above.

As Carl Sagan so evocatively put it, "It is no wonder that our ancestors worshiped the stars.  For we are their children."

In her new book The Human Cosmos: Civilization and the Stars, scientist and author Jo Marchant looks at this connection through history, from the time of the Lascaux Cave Paintings to the building of Stonehenge to the medieval attempts to impose a "perfect" mathematics on the movement of heavenly objects to today's cutting edge astronomy and astrophysics.  In a journey through history and prehistory, she tells the very human story of our attempts to comprehend what is happening in the skies over our heads -- and how our mechanized lives today have disconnected us from this deep and fundamental understanding.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]