Spin cycle

Well, The Daily Mail Fail is at it again, this time with a claim that the CIA has declassified a book predicting the end of the world (which is going to happen soon, of course).  Illustrating the fact that there is no conspiracy theory so blatantly idiotic that there won't be people passionately espousing it, the whole thing has the End Times crowd running around making excited little squeaking noises, while the rest of us are wearing expressions like this:

The book is called The Adam and Eve Story, which should put you on notice immediately that we're not talking about hard science, here.  It's by a guy named Chan Thomas, a "former U.S. Air Force employee, UFO researcher, and self-acclaimed psychic," for whom, we're told, "there are no official records of [his] working directly for the CIA."

So we're definitely off to a flying start.

I guess there's no doubt that the guy's book, which was written in 1966, was considered classified until 2013, and only appeared on the CIA's database of declassified documents about a month ago -- and then, only 55 pages out of the two hundred or so in the original manuscript.  Why it was classified in the first place is uncertain, although it may be nothing more than the fact that anyone who worked on any sort of sensitive-to-security projects -- which Thomas apparently did -- automatically has anything they write classified until it can be reviewed and shown not to give away anything that needs to stay secret.

My surmise is the fact that it languished after that because no one at the CIA took it seriously enough to bother reviewing.

Anyhow, Thomas's claim is that there have been cataclysms on the order of every six thousand years, and we're currently overdue.  What happens during these catastrophes illustrates the fact that Thomas shoulda stuck with UFO research, or at least paid better attention during ninth grade Earth Science class, because the first thing that jumps out at me is that he does not understand the difference between the Earth's rotational axis and its magnetic poles.  This leads him to conclude that when the magnetic poles flip -- something that happens around every three hundred thousand years, not six thousand, so he's off by a factor of fifty, but who's counting -- it somehow affects the rotational axis, throwing continents and oceans around like a washing machine on spin cycle.  

The results are hella scary.  Thomas writes:

In a fraction of a day all vestiges of civilization are gone, and the great cities — Los Angeles, San Francisco, Chicago, Dallas, New York — are nothing but legends.  Barely a stone is left where millions walked just a few hours before...  Winds with the force of a thousand armies will shred everything in sight with a supersonic bombardment, as a Pacific tsunami drowns Los Angeles and San Francisco as if they were but grains of sand...  Calamity will overtake the entire North American continent within three hours, as an earthquake simultaneously creates massive cracks in the ground that allow magma to rise to the surface.

So I think we all can agree that this would be bad.  By the time it's all over -- in seven days, he says -- everything will be rearranged, with Antarctica at the equator (melting its huge ice caps), and the Bay of Bengal at what is now the North Pole.

By now you may be wondering what historical cataclysms "every six thousand years" he's basing this on.  I know I was.  You ready?

The Flood of Noah, and six thousand years before that, something about Adam and Eve.  (You might have guessed the latter based on the book's title; I have to admit by that point I'd already forgotten it, so this got an all-new eyeroll from me.)

Scholars of the Bible might be objecting by now that the Book of Genesis doesn't describe any kind of worldwide catastrophe centering around Adam and Eve, just some malarkey about a serpent and an apple and whatnot, and their being the ancestors of all humanity despite supposedly being the first people and having only sons.  But Thomas seems sufficiently detached from reality that this is only a minor quibble compared to some of the other stuff he says.

Despite the fact that the claim is (in a word) ridiculous, I've already seen three videos on TikTok that seem to treat the whole thing as deadly serious, with the fact that three-quarters of the original manuscript is still classified being used as evidence that the CIA is "hiding something" and "they're trying to prevent mass panic."

Trust me, the only people out there panicking over this are ones who see messages from God on their grilled cheese sandwiches.  And it hardly bears pointing out that you can't use pages you've never seen as proof of anything, given that by default we don't know what's in them.

Sometimes absence of evidence really is evidence of absence.

In any case, I wouldn't lose any sleep over this.  But I will appeal to the conspiracy theorists: can you please try and give me better material to work with?  Because this one was kind of bottom-of-the-barrel.  Time to step up your game, folks.  It's positively making me pine for the good old days of HAARP and Nibiru and the Annunaki and "Birds Aren't Real."

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Watch your tone!

You probably know that there are many languages -- the most commonly-cited are Mandarin and Thai -- that are tonal.  The pitch, and pitch change across a syllable, alter its meaning.  For example, in Mandarin, the syllable "ma" spoken with a high steady tone means "mother;" with a falling then rising tone, it means "horse."

If your mother is anything like mine was, confusing these is not a mistake you'd make twice.

A pitch vs. time graph of the five tones in Thai [Image licensed under the Creative Commons Thtonesen.jpg: Lemmy Laffer derivative from Bjankuloski06en, Thai tones, CC BY-SA 3.0]

English is not tonal, but there's no doubt that pitch and stress change can communicate meaning.  The difference is that pitch alterations in English don't change the denotative (explicit) meaning, but can drastically change the connotative (implied) meaning.  Consider the following sentence:

He told you he gave the package to her?

Spoken with a neutral tone, it's simply an inquiry about a person's words and actions.  Now, one at a time, change which word is stressed:

• He told you he gave the package to her?  (Implies the speaker was expecting someone else to do it.)
• He told you he gave the package to her? (Implies surprise that you were told about the action.)
• He told you he gave the package to her? (Implies surprise that you were the one told about it)
• He told you he gave the package to her? (Implies the speaker expected the package should have been paid for)
• He told you he gave the package to her? (Implies that some different item was expected to be given)
• He told you he gave the package to her? (Implies surprise at the recipient of the package)

Differences in word choice can also create sentences with identical denotative meanings and drastically different connotative meanings.  Consider "Have a nice day" vs. "I hope you manage to enjoy your next twenty-four hours," and "Forgive me, Father, for I have sinned" vs. "I'm sorry, Daddy, I've been bad."

You get the idea.

All of this is why mastery of a language you weren't born to is a long, fraught affair.

The topic comes up because of some new research out of Northwestern University that identified the part of the brain responsible for recognizing and abstracting meaning from pitch and inflection -- what linguists call the prosody of a language.  A paper this week in Nature Communications showed that Heschl's gyrus, a small structure in the superior temporal lobe, actively analyzes spoken language for subtleties of rhythm and tone and converts those perceived differences into meaning.

"Our study challenges the long-standing assumptions how and where the brain picks up on the natural melody in speech -- those subtle pitch changes that help convey meaning and intent," said G. Nike Gnanataja, who was co-first author of the study.  "Even though these pitch patterns vary each time we speak, our brains create stable representations to understand them."

"The results redefine our understanding of the architecture of speech perception," added Bharath Chandrasekaran, the other co-first author.  "We've spent a few decades researching the nuances of how speech is abstracted in the brain, but this is the first study to investigate how subtle variations in pitch that also communicate meaning are processed in the brain."

It's fascinating that we have a brain area dedicated to discerning alterations in the speech we hear, and curious that similar research on other primates shows that while they have a Heschl's gyrus, it doesn't respond to changes in prosody.  (What exact role it does have in other primates is still a subject of study.)  This makes me wonder if it's yet another example of preaptation -- where a structure, enzyme system, or gene evolves in one context, then gets co-opted for something else.  If so, our ancestors' capacity for using their Heschl's gyri to pick up on subtleties of speech drastically enriched their abilities to encode meaning in language.

But I should wrap this up, because I need to go do my Japanese language lessons for the day.  Japanese isn't tonal, but word choice strongly depends on the relative status of the speaker and the listener, so which words you use is critical if you don't want to be looked upon as either boorish on the one hand, or putting on airs on the other.

I wonder how the brain figures all that out?

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Birds, bees, etc.

Yesterday I was thinking about sex.

Not like that.  My intention is to keep this blog PG-13.  I meant sexual reproduction in general, and the topic comes up because I just finished reading Riley Black's lovely new book When the Earth Was Green: Plants, Animals, and Evolution's Greatest Romance, which looks at paleontology through the lens of botany.  It's a brilliant read, the writing is evocative and often lyrical, and it needs to be added to your TBR list if you've even the slightest bit more than a passing interest in the past.

One of the topics she looks at in some detail is how sexual reproduction in plants -- better known as pollination -- led to an inseparable relationship between flowering plants and their pollinators.  A famous example is Darwin's orchid (Angraecum sesquipedale), a Madagascar species with night-scented white flowers whose nectaries are at the base of an impossibly long tube:

[Image licensed under the Creative Commons Bernard DUPONT from France, Darwin's Orchid (Angraecum sesquipedale) (8562029223), CC BY-SA 2.0]

Its discovery prompted Charles Darwin to predict that there must be a moth on the island whose mouthparts fit the flower, and which was responsible for pollinating it.  Sure enough, in a few years, biologists discovered the Madagascar hawk moth (Xanthopan morganii):

[Image licensed under the Creative Commons Nesnad, Xanthopan morganii praedicta Sep 16 2021 03-58PM, CC BY 4.0]

The problem is, such dramatic specialization is risky.  If something happens to either member of the partnership, the other is out of luck.  In fact, sexual reproduction in general is a gamble, but its advantages outweigh the risk, and I'm not just talking about the fact that it's kind of fun.

Asexually-reproducing organisms, like many bacteria and protists, some plants and fungi, and a handful of animals, have the advantages that it's fast, and only requires one parent.  There's a major downside, however; a phenomenon called Muller's ratchet.  Muller's ratchet has to do with the fact that the copying of DNA, and the passing of those copies on to offspring, is not mistake-proof.  Errors -- called mutations -- do happen.  Fortunately, they're infrequent, and we even have enzymatic systems that do what amounts to proofreading and error-correction to take care of most of them.  A (very) few mutations actually lead to a code that works better than the original did, but the majority of the ones that slip by the safeguards cause the genetic message to malfunction.

It's called a "ratchet" because, like the handy tool, it only turns one way -- in this case, from order to chaos.  Consider a sentence in English -- space and punctuation removed:

TOBEORNOTTOBETHATISTHEQUESTION

Now, let's say there's a random mutation on the letter in the fourth position, which converts it to:

TOBGORNOTTOBETHATISTHEQUESTION

The message is still pretty much readable, although the second word is now spelled wrong.  But most of us would have been able to figure out what it was supposed to say.

Now, suppose a second mutation strikes.  There is a chance that it would affect the fourth position again, and purely by accident convert the erroneous g back to an e, but that likelihood is vanishingly small.  This is called a back mutation, and is more likely in DNA -- which, of course, is what this is an analogy to -- because there are only four letters (A, T, C, and G) in DNA's "alphabet," as compared to the 26 English letters.  But it's still unlikely, even so.  You can see that at each "generation," the mutations build up, every new one further corrupting the message, until you end up with a string of garbled letters from which not even a cryptographer could puzzle out what the original sentence had been.

Sexual reproduction is a step toward remedying Muller's ratchet.  Having two copies of each gene (a condition known as diploidy) makes it more likely that at least one of them still works.  Many genetic diseases -- especially the ones inherited as recessives -- are losses of function, where copying errors have caused that stretch of the DNA to malfunction.  But if you inherited a good copy from your other parent, then lucky you, you're healthy (although you can still pass your "hidden" faulty copy on to your children).

This, incidentally, is why inbreeding -- both parents coming from the same genetic stock -- is a bad idea.  It doesn't (in humans) cause problems in brain development, which a lot of people used to think.  But what it does mean is that if both parents have a recent common ancestor, the faulty genes one of them carries are very likely the same ones the other does, and the offspring has a higher chance of inheriting both damaged copies and thus showing the effects of the loss of function.  It's this mechanism that explains why a lot of human recessive genetic disorders are characteristic of particular ethnic groups, such as cystic fibrosis in northern Europeans, Tay-Sachs disease in Ashkenazic Jews, and malignant hyperthermia in French Canadians.  It only happens when both parents are from the same heritage -- which is why "miscegenation laws," preventing intermarriage between people of different races or ethnic backgrounds, are exactly backwards.  Mixed-race children are actually less likely to suffer from recessive genetic disorders -- the mom and dad each had their own "genetic load" of faulty genes, but there was no overlap between the two sets of errors.  Result: healthy kid.

The difficulty, of course, is that despite its genetic advantages, sexual reproduction requires a genetic contribution from two parents.  This is tough enough with mobile species, but with organisms that are stuck in place -- like plants -- it's a real problem.  Thus the hijacking of animals as carriers for pollen, and the evolution of a host of mechanisms for preventing self-pollination (which cancels out the advantage of higher variation, given that once again, both sets of genes come from the same parent).

What's most curious about sexual reproduction is that we don't know how it started.  Even some very simple organisms have genetic exchange mechanisms, such as conjugation in bacteria, which help them not to get clobbered by Muller's ratchet, and something like that is probably how it got going in the first place.  We know sexual reproduction is evolutionarily very old, given that it's shared by the majority of life on Earth, but how the process of splitting up and recombining genetic material every generation first started is still a mystery.

Anyhow, that's our consideration of birds, bees, and others for the day.  I'll end by saying again that you should buy Riley Black's book, because it's awesome, and gives you a vivid picture of life at various times on Earth, not from the usual Charismatic Megafauna viewpoint, but from the perspective of our green friends and neighbors.  It's refreshing to consider how life is experienced from an entirely different angle every once in a while.

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Lost horizon

While our knowledge of the origin of the universe has grown tremendously in the past hundred years, there are still plenty of cosmological mysteries left to solve.

One of the most vexing is called the horizon problem.

It's one of those situations where at first, it seems like "where's the problem?"  Then you look into it a little more, and kind of go, "... oh."  The whole thing has to do with how fast a change can percolate through a system.  Amongst the (many) outcomes of the General Theory of Relativity, we are reasonably certain that the upper bound at which disturbances of any kind can propagate is the speed of light.

So if a change of some sort happens in region A, but it is so far away from region B that there hasn't been enough time for light to travel between the two, it is fundamentally impossible for that change to have any effect at all in region B.  Such regions are said to be causally disconnected.

So far, so good.  The thing is, though, there are plenty of sets of causally disconnected regions in the universe.  If at midnight in the middle of winter you were to aim a very powerful telescope straight up into the sky, the farthest objects you could see are on the order of ten billion light years away.  Do the same six months later, in midsummer, and you'd be looking at objects ten billion light years away in the other direction.  The distance between the two is therefore on the order of twenty billion light years (and this is ignoring the expansion of the universe, which makes the problem even worse).  Since the universe is only something like 13.8 billion years old, there hasn't been enough time for light to travel between the objects you saw in winter and those you saw in summer.

Therefore, they can't affect each other in any way.  Furthermore, they've always been causally disconnected, at least as far back as we have good information.  By our current models, they were already too far apart to communicate three hundred thousand years after the Big Bang, the point at which decoupling occurred and the 2.7 K cosmic microwave background radiation formed. 

Herein lies the problem.  The cosmic microwave background (CMB for short) is very nearly isotropic -- it's the same no matter which direction you look.  There are minor differences in the temperature, thought to be due to quantum fluctuations at the moment of decoupling, but those average out to something very close to uniformity.  It seems like some process homogenized it, a bit like stirring the cream into a cup of coffee.  But how could that happen, if opposite sides of the universe were already causally disconnected from each other at the point when it formed?

A map of the CMB from the Wilkinson Microwave Anisotrophy Probe [Image is in the Public Domain courtesy of NASA]

It's worse still, however, which I just found out about when I watched a video by the awesome physicist and science educator Sabine Hossenfelder a couple of days ago.  Because a 2003 paper found that the CMB isn't isotropic after all.

I'm not talking about the CMB dipole anisotropy -- the fact that one region of the sky has CMB a little warmer than average, and the opposite side of the sky a little cooler than average.  That much we understand pretty well.  The Milky Way Galaxy is itself moving through space, and that creates a blue shift on one side of the sky and a red shift on the other, accounting for the measurably warmer and cooler regions, respectively.

What Hossenfelder tells us about is that there's an anisotropy in the sizes of the warm and cool patches.  It's called the hemispherical power spectrum asymmetry, and simply put, if you sort out the sizes of the patches at different temperatures, you find that one side of the sky is "grainier" than the other.  Like I said, we've known about this since 2003, but there was nothing in any of the models that could account for this difference, so cosmologists kind of ignored the issue in the hopes that better data would make the problem go away.

It didn't.  A recent paper using newly-collected data from the Planck mission found that the hemispherical power spectrum asymmetry is real.

And we haven't the first idea what could have caused it.

In a way, of course, this is tremendously exciting.  A great many scientific discoveries have started with someone looking at something, frowning, and saying, "Okay, hang on a moment."  Here we have something we already didn't understand (CMB isotropy and the horizon problem) gaining an added layer of weirdness (it's not completely isotropic after all, but is anisotropic in a really strange way).  What this shows us is that our current models of the origins of the universe are still incomplete.

Looks like it's a good time to go into cosmology.  In what other field is there a universe-sized problem waiting to be solved?

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The undiscoverable country

After Thursday's post about nonexistent islands, a loyal reader of Skeptophilia asked me if I'd ever heard of the country of Listenbourg.

I said, "Do you mean Luxembourg?" but he assured me he was spelling it right.

"Islands aren't the only thing that can be nonexistent," he said, which is true, but when you think about it too hard is a very peculiar statement.

So I looked into Listenbourg, and it's quite a story -- especially since the whole thing started as a way to ridicule Americans for their ignorance about anything outside the borders of the United States.

In October of 2022, a French guy named Gaspard Hoelscher posted a doctored map of Europe on Twitter that looked like this:

He captioned it, "Je suis sûr que les américains ne connaissent même pas le nom de ce pays!" ("I'm sure that Americans don't even known the name of this country!")  One of his followers responded, "Qui ne connaît pas le Listenbourg?" ("Who doesn't know Listenbourg?")

You'd think anyone who'd ever given more than a ten-second look at an actual map of Europe would immediately know this was a joke, but no.  Even a closer look at this map would have revealed the curious fact that "Listenbourg" is actually a resized and inverted copy of the outline of France itself, simply pasted onto (and partially covering) the northwest corners of Spain and Portugal.

Apparently, this was not the case, as the original post caused a number of irate Americans to jump up and defend our superior knowledge -- almost none of whom, however, came right out and said that they recognized it was a prank.  You could tell that some of them had actually come damn close to saying, "Of course I know where Listenbourg is," but held back at the last minute.

This prompted a flood of hilarity online that the prank's originator, Hoelscher, said "totally overwhelmed" him.  Amused Europeans invented a flag, capital city ("Lurenberg"), culture, history, language, and even a national anthem for Listenbourg.  It has five regions, they said: Flußerde, Kusterde, Mitteland, Adrias and Caséière.  A post saying that Hoelscher himself was the president was met by universal acclaim.  Then it escaped social media into the wider world:

• An announcement prior to the Paris Olympics of 2024 stated that "The number of Olympic delegations has risen from 206 to 207 with the arrival of Listenbourg."
• Amazon Prime in Europe announced that a documentary on the history of Listenbourg was in production -- only careful watchers noticed that the projected release date was "February 31, 2025."
• Ryanair said in a press release that they were "Proud to be announcing their new base in Listenbourg."
• The French television network TF1 aired a realistic-sounding weather report for the country.
• French politician Jean Lassalle said in a speech that he was "just returned from a visit to an agricultural seminar in Lurenberg."
• The city of Nice said that they were happy to announce their intention to become a sister city to Lurenberg, and that there would be new inexpensive flights between the two.

I have to admit that as an American, my laughter over all this is coupled with a distinct edge of cringe.  I mean, being global dumbasses is not exactly the reputation I'd like my country to have.  Sadly, though, I can't really argue with the assessment.  You don't have to dig very hard to find highly embarrassing videos of interviewers stopping people in crowds in the United States to ask them tough questions like "What is the capital of England?" and finding numerous Americans who can't come up with the answer.  And with the Republicans currently doing everything in their power to destroy our system of public education, the situation is only going to get worse.

Oh, but don't worry.  At least we'll have the Ten Commandments on the wall of every classroom, and students will get Bible lessons every day and won't be exposed to scary books like Heather Has Two Mommies.

Hey, I wonder what would happen if you asked Donald Trump to find Listenbourg on a map?  I bet he'd never realize he was being pranked, considering that he once gave a speech to African leaders and confidently talked about the proud country of "Nambia."

Look, I know we all have holes in our knowledge; all of us are ignorant about some subjects.  The important thing is not to make ignorance a permanent condition -- or to flaunt it.  Stubbornly persisting in your state of ignorance has a name.

It's called "stupidity."

What's worse is when people think they are experts on stuff when they're clearly not, and publicly trumpet their own idiocy.  (Donald Trump is absolutely the poster child for this phenomenon.)  As Stephen Hawking trenchantly put it, "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."  Because if you're convinced you already know everything you need to know -- and that, I'm afraid, is the state of many Americans, including the majority of our elected officials -- you have no incentive to learn more, or worse, to find out you're actually wrong about something.

My dad used to say "there's nothing as dangerous as confident stupidity."  I think that's spot-on.  And sad that the Listenbourg incident -- funny as it is -- pointed out that in the eyes of many people in the world, that's what the United States represents.

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Stellar slingshot

Sometimes there's a scientific discovery that's just such an "oh, wow!" that I have to tell you about it.

Like the research that I ran into in the Astrophysical Journal recently.  "Origin of a Massive Hyper-runaway Subgiant Star LAMOST-HVS1: Implication from Gaia and Follow-up Spectroscopy," by Kohei Hattori, Monica Valluri, Norberto Castro, Ian U. Roederer, Guillaume Mahler, and Gourav Khullar, of the University of Michigan - Ann Arbor, describes a star that was ejected from our galaxy at a speed that boggles the imagination.

This star -- the euphoniously-named LAMOST-HVS1 -- is traveling at about 570 kilometers per second, on a trajectory almost perpendicular to the plane of the Milky Way Galaxy.  (If it helps, that's over a million miles an hour.)  It was initially thought that the star might have been evicted from the center of the galaxy, where there is an enormous black hole -- only something that massive, scientists thought, could impart enough energy to a star to get it traveling that fast. But tracking its path backward showed that it didn't come from the center, but from a region called the Norma Spiral Arm.

[Image is in the Public Domain, courtesy of NASA/JPL]

What this seems to indicate is that there are massive black holes scattered throughout the galaxy, not concentrated at the center.  Which is vaguely terrifying.  The scenario is apparently that a binary star was drawn in toward the black hole, and as it fell toward the event horizon, one of the two gained enough energy to be flung free -- what's called the "gravitational slingshot effect."  This phenomenon has been used to get countless television and movie spacefarers out of sticky situations, most notably in the 1998 film Lost in Space, wherein we learn that something being a truly awful television show is not sufficient to stop producers from turning it into an even worse movie.  I say "worse," even though the 1960s Lost in Space television show was uncategorically abysmal, because the movie took itself so damn seriously.  When the television show brought out space vikings or space cowboys or space hippies or a space motorcycle gang -- none of which, by the way, I'm making up -- at least they knew they were being campy.

But here, we're actually supposed to believe the intrepid crew of the Jupiter 2, having just escaped from Gary Oldman as a Dr. Smith who has turned into a giant humanoid spider (for the record, I'm not making that up, either), realizes that they don't have enough oomph to escape from the planet that's disintegrating around them, so Matt LeBlanc as Major Don West decides to use the "gravity well" of the planet to fling them free.  So he puts the Jupiter 2 into a power dive, and somehow they go all they way through the planet, miraculously dodging all of the rocks and debris, not to mention an entire mantle and core's worth of molten lava, and get squirted out of the other side like someone spitting out a grapefruit pit.

But I digress.

In any case, the writers of the script actually were referencing a real phenomenon, but one which would be unlikely to save you if you are ever in the situation of having your spaceship run out of gas while trying to escape from an exploding planet.  "This discovery dramatically changes our view on the origin of fast-moving stars," said study co-author Monica Valluri, in a press release.  "The fact that the trajectory of this massive fast-moving star originates in the disk rather that at the Galactic center indicates that the very extreme environments needed to eject fast-moving stars can arise in places other than around supermassive black holes."  (The press release also has a nice gif showing the star's path, which you should all check out.)

All of which is pretty cool, especially since there have only been around thirty of these "hyper-runaway" stars ever observed.  Given its current position, it's interesting to think about what the sky would look like to a denizen of one of its planets (yes, I know, any denizens it may have had surely wouldn't have survived a close encounter with a black hole, but just bear with me here).  I'm reminded of Carl Sagan's comment about a star in that position experiencing not a sunrise but a galaxy-rise -- from where it is, the disc and arms of the Milky Way would fill the entire night sky.

So there's some awe-inspiring research from the astronomers.  I don't see how anyone would not find this astonishing.  Maybe if you were like the Robinson family, meeting hordes of aliens every week, you'd get inured, but I can't help but think I'd still be pretty blown away even so.

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Islands of the imagination

There's a long list of what have been nicknamed "phantom islands" -- islands that have been recorded on maps, sometimes for centuries, but then when people follow the map and go out where the island supposedly is, there's nothing there.

Well, there's something there, namely a shit tonne of salt water.  In one way, it's unsurprising that misidentifications like this can happen; icebergs, pumice rafts from volcanic eruptions, and even low cloud banks in the distance can look like land, and when you couple that with the desperation to reach terra firma a lot of mariners felt after weeks at sea, it's understandable that this sometimes occurred.  What's more curious is how persistent some of these phantom islands were -- there are ones that were only conclusively proven not to exist in the last two decades.

A big part of the problem is that in the days before satellites and GPS, when you were out at sea, it was awfully hard to be certain of exactly where you were.  Latitude, as it turns out, is fairly easy; in the Northern Hemisphere, the altitude of Polaris above the horizon (which you can measure with a sextant) is equal to the latitude.  (It's a little trickier in the Southern Hemisphere -- there is no "South Star" -- but with a little adjustment, the same principle can still be used.)

Longitude, on the other hand, is a whole other can of worms.

You can figure out your longitude using the rising times of various stars, but the hitch is that requires you have an accurate timepiece that isn't thrown off by the incessant jostling and jolting on board ship.  It wasn't until the eighteenth century that such a clock was invented, and it only went into widespread use in the nineteenth -- how this happened is the topic of Dava Sobel's wonderful book Longitude -- but even with more accurate timekeeping, figuring out exactly where in the trackless oceans you were was no easy task.  This is probably what happened with the nonexistent Saxemberg Island, first sighted in 1670, which appeared on maps for almost two hundred years (and was "viewed extensively from a distance" in 1804 and again in 1816).  It's now surmised that they were actually seeing the remote Tristan da Cunha Island, and had simply miscalculated where they were.

One that is likely to have been a combination of inaccurate longitude calculation and seeing something that looked like an island but wasn't is "New South Greenland," which was "discovered" by the curious figure of Captain Benjamin Morrell, originally of New York.  To say that Morrell had a checkered career is a bit of an understatement.  He ran away to become a sailor at age seventeen, served during the War of 1812 (and was captured twice by the British), but eventually rose through the ranks to captain the Wasp, which he took down into Antarctic waters in 1823.  He had a penchant for exaggeration and occasional outright lying, but in this particular case he seems to have simply been mistaken.  He reported an extensive land which he initially thought was part of the Antarctic Peninsula, and sailed along it for five hundred kilometers -- but subsequently he found his position to be ten degrees of longitude (at that latitude, about two hundred kilometers) east of where he thought he was, in a part of the ocean that has no land masses whatsoever and by later sounding was found to be 1,500 meters deep.  So what he saw clearly wasn't part of Antarctica.  What it actually was remains a mystery -- the best guess is a long connected chunk of icebergs.

For what it's worth, Morrell's career didn't improve much thereafter.  He was involved in piracy in China and Madagascar and was lucky to escape with his life, launched a fruitless search for gold in New Guinea, and supposedly died "of a fever" in Mozambique in 1838 -- although a letter with his signature showed up in New York in 1843, leading some people to believe he faked his own death to get away from all the people he'd defrauded or otherwise pissed off.

Sometimes imaginary islands get wrapped up in mythology, and that makes it even harder to tease out what's real and what isn't.  Penglai, "thirty thousand leagues off the east coast of Shandong, China," described as one of the homes of the "Great Immortals," is pretty certainly a tall tale -- although interestingly, there's a legend both in Vietnam and Japan pinpointing an island in more or less the same place (where it's called Bồng Lai and Hōrai, respectively).  Saint Brendan's Isle, supposedly first seen in 512 C.E. by the Irish monk/explorer Saint Brendan of Clonfert, is another one around which wild tales have arisen, but it was reported so persistently that its existence was considered a fact for hundreds of years.  (Its reputation for being the home of devils and demons led a priest in the Canary Islands to perform an exorcism directed toward the entire island in 1723.)  The last alleged sighting of Saint Brendan's Isle was in 1772, but it still appeared on maps -- somewhere off the west coast of Africa -- well into the nineteenth century.

Bedarra Island, off the coast of Australia, which is actually real [Image licensed under the Creative Commons Banfield1 at English Wikipedia, Bedarra Island aerial, CC BY-SA 3.0]

Sometimes islands do exist -- temporarily.  This seems to be the case with Bermeja, discovered by Spanish explorers off the coast of the Yucatán Peninsula in 1539, and extensively described (along with its precise location) by other mariners in the sixteenth century.  Expeditions to find it later proved unsuccessful, although close to the reported location there is a significant seamount.  It's likely that Bermeja was the victim of a combination of erosion and tectonic shifting, and what was once dry land now isn't.

A lot of them, though, have eluded explanation except as mirages.  This is almost certainly the case with the aptly-if-unfortunately-named Fata Morgana Island (a fata morgana is a common type of mirage experienced at sea, especially in polar regions).  The explorers Johan Peter Koch and Aage Bertelsen reported it -- once again, along with an exact location, off the northeast coast of Greenland -- in 1907, and its existence was confirmed from the air by Koch's son Lauge in 1933.  Unfortunately for all three of them, there's no land there, just lots of extremely cold salt water.  The sightings were undoubtedly a combination of mirages and wishful thinking.

In any case, our precision GPS systems, satellite photography, and (I hope) less tendency to fall for fanciful tall tales has improved our ability to discern between what's real and what's not.  Although I have to say I'm kind of disappointed that Antillia isn't real.  A favorite claim amongst the Spanish and the Portuguese until the sixteenth century, at which point their own explorers came back and reported that there wasn't anything where it allegedly was but a big blob of the Atlantic Ocean, Antillia supposedly had seven cities run like some utopian paradise, where everyone lived in harmony and there was no crime or violence, and its leaders were wise, kind, and benevolent.  I don't know about you, but if that one is ever rediscovered, I'm buying a plane ticket.

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