hudebnik | Entries tagged with science

20:53 EST: Mars is close enough to the full Moon that, despite being near inferior opposition and about as bright as it ever gets, I can't see Mars with the naked eye. With binoculars, I can see a maybe-reddish pin-prick less than half a Lunar diameter away from the Moon. At 21:21, Mars is scheduled to go behind the Moon, to emerge out the other side an hour later.

So I was trying to figure out, from first principles, how and when eclipses happen. The Moon's orbital plane and the Earth's orbital plane don't exactly agree, and an eclipse can happen only when the Moon is in (or close enough to) the Earth's orbital plane -- not too high, not too low. It can also happen only when the Moon is on (or close enough to) the line between the Earth and the Sun. Combining these facts, an eclipse (lunar or solar) can only happen when the line determined by the intersection of these two planes matches (reasonably closely) the line between the Earth and the Sun. Which should happen twice a year, so those are the only times of year that an eclipse should be possible.

And yet in recent years there have been solar eclipses in both August and May, three months (90°) apart. How is this possible? I thought "perhaps the angle between the Moon's and Earth's orbital planes is small enough that 'close enough' happens frequently." So I Googled "what's the angle between the Earth's orbit and the Moon's orbit?" and got 5.145°. Since the Moon and the Sun are each only half a degree wide as seen from the Earth, that should mean that at its highest (northernmost) point, the Moon is ten times too high to be involved in an eclipse, and since it's a roughly sinusoidal curve that spends less time near its mean than near its extremes, "close enough" probably doesn't happen frequently.

But the page that gave me the 5.145° figure was at eclipse.gfsc.nasa.gov, which goes into lots of detail about the Moon's orbit. In particular, one of my assumptions fails: the Moon's orbital plane isn't quite fixed relative to the sidereal background. The time from one ascending crossing of the ecliptic to the next (the "draconic month") averages 27.211 days, while the sidereal month averages 27.322 days, so the Moon's orbital plane precesses by 360° every 18.6 years. So the times of year that eclipses are possible, based on my reasoning above, should also follow a cycle of 18.6 years.

Furthermore, actual draconic months vary by several hours above and below the aforementioned 27.211 days, correlating with the direction of the sun: the longest draconic months are when the line of intersection of the two orbital planes matches the Earth-Sun line (i.e. when eclipses are possible), and the shortest draconic months are when those two lines are perpendicular. Further furthermore, the amplitude of this variation follows a multi-year cycle that the Web page points out but doesn't explain (or I've missed the explanation).

In addition to the sidereal month (from alignment with the background of "fixed" stars to the next such alignment) and the draconic month (from ascending node to ascending node), the page also discusses the synodic month (from new moon to new moon) and the anomalistic month (from perigee to perigee). All of these are relevant to calculating eclipses. No two of these months are quite the same length, and each of them (perhaps except the sidereal?) varies significantly from one month to the next, with different patterns of variations. Wow.

Landed at JFK a bit before noon Sunday after three weeks in Spain. Caught a cab home. House still standing; different flowers blooming in front yard than before we left.

Unpacked suitcases. Repacked suitcases. Drove 4+ hours north to friends' house. Slept a lot. With five friends and two other cars, drove north another hour or so into the path of totality, found parking place near a restaurant/resort and gas station, and sat around for a few hours waiting for an eclipse.

We were worried that there would be too much cloud cover, but as it turned out there were only a few high, thin clouds. We viewed the increasing amount of eclipse variously through eclipse glasses, in a camera obscura, by projecting through binoculars onto a white piece of foamcore, and by projecting through a kitchen colander ditto. A breeze sprang up, the air got chilly, the light got weird, and then in a matter of seconds the last sliver of sun projected on the foamcore disappeared, the sky turned midnight-blue, and a cheer went up from the crowd. We could see the eclipsed sun perfectly, with a fair amount of corona and one persistent red flare. We could also see Venus nicely, maybe ten degrees away from the sun and moon; I gather some other planets were supposed to be visible too but I didn't spot them. Anyway, after two minutes or so, several more flares or Bailly's-beads or something appeared next to the first one, then merged into a blaze of white and totality was over.

Within seconds, cars started moving, jockeying to get out of the parking lot and onto the road. We waited for the majority of them to leave before getting in the car ourselves. One of our friends had picked out a restaurant a few miles to the south where we could get dinner, gave us its name, and we all hit the road in our various cars... except that we couldn't get any cell phone service (it's a remote area, and there were suddenly thousands of cell phones trying to use one tower). So after crawling along the interstate for half an hour in bumper-to-bumper traffic,

shalmestere and I took the relevant exit and stopped at a gas station to ask where the restaurant was. The lady behind the counter gave clear directions, and we got back on the road. In another heavy traffic jam, presumably people trying to avoid the heavy traffic jam on the interstate. It took another half hour or so to crawl a few miles to the restaurant, where we found we couldn't get a table for seven and started looking for someplace else to eat.

Most restaurants in this part of upstate New York exist to serve weekenders and summer people, so since this was neither a weekend nor summer, they were closed. After a bunch of walking up and down the road, and continuing trouble getting cell signal, we found a place where we could at least sit near one another, and had dinner while waiting for (hopefully) the worst of the traffic to subside.

Left the restaurant just before 7 PM. Traffic was indeed less bad than before, but in the first two hours (mostly on interstate) we travelled 63 miles. Including stops for gas and driver-switching, we got home at the stroke of 1:00 AM, thoroughly fried. Fall down go boom, in own bed for the first time since March 13-14. Both have to work in the morning, but at least we don't have to physically go to our respective offices.

Big events in the news in the past 24 hours.

The world's population hit 8 billion.

An explosion in Poland (just over the border from Ukraine) possibly caused by a Russian missile, which (if true and intentional) would draw all of NATO into the war.

Donald Trump announced he's running for President again, in hope of avoiding criminal prosecution for things he did on his way out of the White House the last time (although the announcement costs him several important income streams).

Un-humanned Artemis rocket lifted off, heading for orbit around the Moon and return to Earth.

And I have a cold: scratchy throat, PND, headache, etc. As of yesterday mid-day, normal oxygen saturation and no fever; I'll do a Covid test tonight (since tomorrow is my usual "go to the office" day).

shalmestere is going to her office today, so she took a Covid test last night: negative.

siderea linked to this article on the sex lives of White-Throated Sparrows, which inspired this post.

But first, consider how sexual reproduction works in our world, in our species. I'm only talking about biological/chromosomal sex here, not anatomical or social or legal, and for simplicity I'm assuming that every individual is of one unambiguous biological/chromosomal sex -- no XXY or XYY trisomies. A man and a woman can produce offspring of either sex; both sons and daughters are genetically close to both of their parents (although sons are slightly closer to their fathers because that's where they got their unpaired Y chromosome). The result is basically a single gene pool for the whole species (except for mitochondrial DNA and a few Y-linked genes).

Now imagine that each human carried only one sex chromosome, rather than a pair, and that men and women were both capable of homosexual reproduction: two women could produce a (necessarily female) child, and two men could produce a (necessarily male) child. If this happened only occasionally, it wouldn't have much effect on the population. But if homosexual reproduction were universal, there would be genetic divergence, with males and females gradually becoming two mostly-separate gene pools and then two separate species. If there were an occasional instance of heterosexual reproduction against a mostly-homosexual background, the offspring would have genetic material from both pools, and thus (if the offspring reproduced) pull the two pools back together.

So, back to the sparrows. White-throated sparrows have two genetically-determined color morphs: brown-streaked and white-streaked, each forming roughly half of the population. If brown-streaked sparrows preferred to mate with other brown-streaked sparrows, and white-streaked with white-streaked, they would diverge genetically over time and we'd eventually have two separate species: brown-streaked and white-streaked. But in fact, females (both brown- and white-streaked) prefer brown-streaked males, while males (both brown- and white-streaked) prefer white-streaked females. As a result, white-streaked females and brown-streaked males get their pick of mates, which is each other, leaving the remaining brown-streaked females and white-streaked males to make do with one another. As a further result, essentially all mated pairs are either white-streaked-female to brown-streaked-male or brown-streaked-female to white-streaked male. Both sorts of pairs can produce any combination of male, female, brown-streaked, and white-streaked, so there's no genetic isolation and no speciation event: there are effectively four "sexes", but they're all still bound together into a single genetic population.

(Another point in the article: brown-streaked sparrows of both sexes tend to be more nurturing, while white-streaked sparrows of both sexes are more aggressive. Which has interesting implications of its own, but it's peripheral to the point I'm making here.)

By amazing coincidence, the same day that I read that article, I read Ursula LeGuin's short story "The Wild Girls", about a human society with three castes named Crown (nobility), Root (merchant class), and Dirt (slaves). In our world, wherever a caste system has arisen, cross-caste marriage is strongly discouraged if not forbidden, which (given enough time, and strict enough enforcement) would be expected to produce genetic divergence and speciation. But in "The Wild Girls", cross-caste marriage is mandatory: Crown men are only allowed to marry Dirt women, Dirt men with Root women, and Root men with Crown women. It's not entirely clear in the story, but I think a child's caste is always the same as its father's. In any case, there are effectively six "sexes", and they're all bound together stably into a single genetic population by the cyclic marriage rules. And although you can tell someone's caste by clothing, there's no genetic difference among castes and thus probably no way to tell the caste of a naked person. (Which raises plot ideas....)

And then I thought about fingerloop braiding. Consider a simple two-loop "braid", as discussed here. There are two interesting operations you can do: you can pass one loop through the other, and you can twist a loop on its own axis ("taking thy bowes reversed", as the middle English source says). If you just twist each loop on its own axis, never passing one through the other, you end up with two independent two-ply twisted cords, connected only at the anchor. If you only pass one through the other, never twisting either one, you again end up with two two-ply twisted cords, connected at both ends but otherwise independent. But if you pass one through the other, then twist one, in alternation, the two operations lock one another in place and you end up with a single four-strand braid. Likewise if you have three, or four, or five loops: if you only twist each one, you get five independent two-ply cords; if you only pass them through one another, but always "taking thy bowes unreversed", you get two 3-ply, 4-ply, or 5-ply braids connected to one another only at the ends. But if you pass loops through one another and reverse them, alternating operations reasonably often, you get a single bound-together braid of 6, 8, or 10 strands. If there's an occasional reversal in a mostly-unreversed braid, you get a cord with large "eyes", holes where the two halves run parallel but independent between one linkage and the next.

Do with that what you will.

Last month we did some book triage, looking for books that we could bear to give away to save storage space, and ran across a copy of Stephen Jay Gould's Full House. Apparently my mother gave it to me for Christmas 25 years ago, it wasn't at the top of the pile of books to read on Christmas afternoon, and I somehow never got to it. So I'm reading it now.

Gould's target in this book is the idea of "progress" in evolution: the idea that evolution through natural selection produces successively "better", or at least larger and more complex, organisms, because large size and complexity (however you define that) are generally pro-survival traits. Even today, and more so in the 1990's when he wrote the book, the standard popular image of evolution is of a ladder from bacteria to algae to jellyfish to trilobites to reptiles to mammals to primates to humans. And we see the same within lineages: we've all seen the picture of the evolution of horses from the dog-sized Eohippus to modern horses, donkeys, and zebras, and of primates from lemurs to monkeys to apes to humans, all illustrating the trend towards greater size and greater "complexity" or "sophistication".

And Gould says, in a nutshell, there is no such trend -- or if it is, it indicates a statistical artifact, rather than any advantage inherent in large size or "complexity". (In particular, modern horses represent not a pinnacle of evolutionary perfection but the pitiful remnants of a failed evolutionary branch: 5-10 million years ago there were dozens of genera, in a wide variety of sizes, then they all died out except Equus, and then a million years ago Equus died out over 90% of its geographical range, spreading a few species again only with the help of human domestication.)

What we perceive as a trend appears for several reasons.

We tend to pay attention to the largest or "best" of any group. If we're looking at batting averages in Major League Baseball (as Gould does for about a third of the book, to illustrate his point), it's easy to look up the best averages in the league, but much harder to find the worst averages in the league, because nobody's interested in those. If, hypothetically, the mean batting average were to stay the same but the standard deviation increased or decreased, we would perceive the maximum increasing or decreasing, not because batters as a whole are getting better or worse, but because they are getting more varied or more uniform. When Gould analyzed not only the best but the worst batting averages in MLB from year to year, he found them moving symmetrically: on rare occasions, either or both might move away from the mean, but in most years, they both move towards the mean (precisely what one would expect from a sport as it matures and standardizes on better ways of doing things).

But why would the mean be staying the same? Wouldn't you expect overall batting skill to get better over the decades? Yes, but pitching and fielding skill also get better over the decades. And whenever some technological or technical breakthrough has given an advantage to one over the other, the rules have been changed to "restore the balance"; as a result, the mean batting average in MLB has been remarkably constant for a hundred years.

Gould concludes that the "extinction of the .400 hitter" (nobody's hit .400 in a season since, IIRC, 1941) indicates not a degradation in play, but rather of an improvement (and, more importantly, a uniformization) of play: as the bell curve of performance gets narrower, there are fewer and fewer examples at any given distance away from its peak.

The reverse happens in biology: the real trend in evolution is increased variation among individuals of a species, among species, among genera, etc. (Until there's a mass-extinction event, at which point most of the groups disappear completely, and the survivors start over, increasing in variation again from their new starting point.) If we pay attention preferentially to the largest or "most complex" members of any group, as seems to be the human tendency, we'll perceive a trend towards increasing size or complexity when in fact there's only a trend towards increasing variability.

If a drunk is walking along a sidewalk with a wall on his left and a gutter on his right, randomly staggering to left or right, he'll eventually end up in the gutter -- not because his stagger is biased towards the gutter, but because when he's close to the wall, he can't move any closer to it; the only direction he can go is away from it. The "bell curve" of his possible paths is truncated on one side, so it's necessarily skewed and asymmetrical. Of course, how long it takes him to fall into the gutter is an exponentially decaying function of the distance from wall to gutter, so if it's a hundred yards, he may die of old age first.

Similarly, there are probably physical limits to how good a human baseball player can be. The maximum fast-ball has been between 100 and 105 MPH for a hundred years; IIUC, nobody has ever thrown 110 MPH, much less 140. As a sport grows and matures, you expect any given performance measure to get steadily better, but as it approaches the physical limits, it will get better slower and slower. And those farthest away from the limits will get better faster than those closer to the limits. For example, when women were first allowed to run marathons with men, their times were much longer, but their rate of improvement from year to year was much faster -- exactly as one would expect because their sport was less mature and they were initially farther from their limits. As a result, one expects to see the best in any field with a hard upper limit get microscopically better while the worst get substantially better, thus drawing the curve tighter and narrower (while remaining skewed away from the wall).

In biology, we know that life developed "from the bottom up", from simple organic molecules, to more complex organic molecules, to self-replicating molecules, to prokaryotic cells, to eukaryotic cells. This isn't necessarily because life "wants" to be more complex, but simply because for any given definition of "life", there's a lower bound of complexity below which something can't meet that definition. If organisms have the option of evolving greater and lesser complexity, some will probably do each, but the ones that fall below the lower bound will die (or at least no longer qualify as "life" for our purposes). So one would predict that a purely random stagger in biological complexity would produce gradually more complex (and exponentially rarer) organisms.

One particularly revealing example involves foraminiferans, a group of microscopic organisms that (fortunately for biologists) produces silica shells that survive nicely in fossil records. The standard way to find them is to take a bunch of silt or sand and filter it through successively finer sieves, recording how many you find at each size. But the finest sieve available in most biology labs is about 150 μm, which means any foraminiferan below that size will never appear in a sieve and therefore in a biology paper. This serves as a "wall", or lower bound, on the size of foraminiferans, not in the wild but in our observations. And, just as one would expect, the data indicate that the maximum and mean size of foraminiferans gradually trend upwards over time, not necessarily because they're actually getting bigger, but because we're seeing the large end of the distribution and ignoring the small end (which may well be getting smaller as the biggest get bigger -- at least, there are still plenty of them near the 150 μm lower bound).

Fortunately, there are several ways to tell the difference between a measure increasing as a statistical artifact, and a measure increasing because of selection pressure.

You can look at not only the maximum but also the minimum: if maxima and minima move symmetrically around the mean, that suggests it's just a change in standard deviation, while if they both move in the same direction, that suggests an actual selection pressure.

You can look at the mode rather than the mean or the median. Means are notoriously susceptible to asymmetric skew: if my brother and I are in a room with Jeff Bezos, the average per capita income in the room is billions, but that doesn't tell you much about my brother or me. Medians are less susceptible to asymmetric skew, but still somewhat. It appears that the mode of vertebrate evolution (whether you count species, individuals, or biomass) is still fish; the mode of multicellular evolution is still arthropods (especially beetles); the mode of life's evolution is still bacteria. If you surveyed all the life on earth objectively, you could be forgiven for not noticing the existence of two tiny evolutionary branches called "plants" and "animals"; if you surveyed all the animals objectively, you might not notice the vertebrates; if you surveyed all the vertebrates, you might not notice the mammals; and if you surveyed all the mammals, you might not notice the existence of humans. At each of these levels of grouping, the overwhelming majority of individuals, species, and biomass are small and "simple", suggesting no evolutionary pressure towards greater size and complexity.

You can look at ancestor/descendant pairs in speciation events. If a "parent" species that's not up against a wall is equally likely to produce "child" species larger or smaller than itself, that suggests a random stagger; if, on the other hand, "child" species consistently tend to be larger than their immediate predecessor species, that suggests an evolutionary pressure for larger size. This is difficult research to do, as it requires identifying lots of ancestor/descendant pairs in an incomplete fossil record, but in most of the cases where it has been done (according to Gould, writing in the 1990's), the results have indicated a random stagger, not a consistent selection pressure. If anything, there's actually a tendency in the direction of simplicity, as formerly-independent organisms become parasites (or at best symbiotes) on other organisms and shed the now-redundant parts of their bodies and genomes.

Wild stuff. And Gould was such a good science writer.

A few nights ago we walked the dogs before bed, and noticed the crescent moon, a bit above the horizon, with a distinct pinkish cast. I pointed it out to

shalmestere, naturally assuming it was pink for the same reason the setting sun is red: it's just above the horizon, and therefore filtered through a lot of atmosphere, dust, and haze.

Last night we walked the dogs before bed, and the moon was now slightly gibbous, farther above the horizon, and still pink. I went "Huh."

Tonight the moon is about 3/4 full, even farther above the horizon, and still distinctly pink. And the only explanation I can think of is smoke from the fires in California and Oregon. The air here in NYC doesn't smell noticeably of smoke, but it has a certain opacity; everything is just a little fuzzy around the edges, as it hasn't been for the past fifteen months. I knew intellectually that this was a really bad fire year on the west coast, but this kind of effect 3000 miles downwind makes it much more real and visceral.

Edit: See this site for real-time Air Quality Index measurements and forecasts. The forecast for yesterday was red, today and tomorrow green, but the actual real-time measurements in most of the NYC area this morning are orange. Perhaps the forecast for today is lower because of the forecast thunderstorms this afternoon. One can also easily compare different kinds of pollution -- overall AQI, particulates under 2.5µm, ozone, sulfur dioxide, and carbon monoxide. For example, AQI, PM_2.5, and CO were all in the red yesterday, as one would expect from wildfire smoke, while ozone and SO₂ were both in the green.

See this Wired article.

TLDR: WHO and CDC guidance about COVID (and flu, for that matter) has been based on it being spread by large (over 5 microns) droplets that travel only a few feet, not by smaller (under 5 microns) aerosol particles that can hang in the air for minutes or hours, and travel hundreds of feet. But in fact, particles larger than 5 microns can hang in the air for minutes or hours, and travel hundreds of feet; a better dividing line for that purpose would be 100 microns, and there was research to that effect over 80 years ago. It turns out the 5-micron threshold comes from somebody in the 1950's writing about tuberculosis, which (unlike most infectious agents) is only dangerous if it gets deep into the lungs, and the nose filters out most particles over 5 microns, preventing them from getting deep into the lungs. There was never any evidence that 5 microns was a meaningful distinction between "droplets" and "aerosols". One researcher in the 1960's conflated several unrelated statements by another researcher, and we've been giving bad public-health advice based on that mistake ever since, affecting not only COVID, but influenza and other infectious diseases.

For related thoughts on chasing down the history of statements in academic research, see "The Problem of Ruritanian Purple Feathers", Tournaments Illuminated 77 (Winter 1985), reprinted in Knowne Worlde Handbook but apparently not on the Web anywhere.

There was a lunar eclipse the night of July 4. I didn't hear about it in advance, and didn't notice anything different about the moon that night except that it was remarkably full.

But last night the still-almost-full moon formed an almost equilateral triangle, maybe two degrees on a side, with Jupiter and Saturn, both of which (being in the same direction as the full moon) are near inferior opposition and thus as bright as they ever get. And the Earth happens to have been at aphelion, the farthest it ever gets from the Sun, on July 4, which means we're ever-so-slightly closer to Jupiter and Saturn than we would have otherwise been, making them (let's see...) 1.6% brighter than if this same conjunction had happened when we're at perihelion.

Or more properly "speculative fiction".

There are various aspects of our current predicament that have been explored by SF authors in the past. Some that I know of:

Philip Roth's The Plot Against America. I haven't actually read this one, but I hear that it's relevant to the Trump presidency.

Octavia Butler's The Parable of the Talents, in which a populist demagogue wins the Presidency on the slogan "Make America Great Again" and a lot of sucking-up to the religious right. But one gets the impression in the book that he's a competent adult, not a petulant toddler, and that he actually believes some of the religious-right stuff he spouts.

"Being There", the movie starring Peter Sellers as a mentally handicapped gardener who makes decisions and pronouncements by watching TV, and by the end of the movie is the Republican nominee for President. But he's gentle and good-natured.

Robert W. Sawyer's WWW: Wake, in which a highly-contagious disease jumps from animals to humans in a remote Chinese province. The Chinese government exterminates the human population of the infected area and temporarily shuts down China's Internet connections to the rest of the world to prevent the story from leaking.
(Not really a spoiler: that all happens in the first few chapters of book 1 of a trilogy.)

And of course lots of people have written about racial conflicts in the U.S.

But there must be an already-written SF story in which a modern industrialized society responds to a pandemic by shutting down face-to-face businesses and social contact, and the effects of this. Such as what happens if workers don't go back to the office?, and how children who grow up being told not to leave the house or be within 6 feet of anybody outside the family will adjust when it's over.

As the OED points out, today is Isaac Asimov's 100th birthday.

Isaac Asimov was a formative influence on me. He was a decent science fiction writer (with occasional flashes of brilliance -- The Gods Themselves springs to mind), a good mystery writer, and an AWESOME non-fiction writer. For umpty-ump years he had a monthly column in The Magazine of Fantasy and Science Fiction in which he could discuss pretty much whatever topic he wished, and he used that freedom to the fullest, covering topics from biochemistry (his Ph.D. subject) to astrophysics to geography to etymology to history to myth to... pretty much anything. Periodically these columns were collected and published in book form, and throughout my pre-teen and teenage years a good fraction of my bookshelf was these books of collected free-form articles, which I read and re-read voraciously. Another good chunk of my leisure reading was his book-length non-fiction, e.g. The Roman Republic and The Roman Empire.

And of course, he was mind-bogglingly prolific. It took me several years to write a textbook; he wrote at least two books each year from 1950 to 1993, and frequently half a dozen or more in a year, a mix of textbooks, popular non-fiction, and fiction.

Back to the science fiction, for which he's probably best known. He was never a master of character or dialogue, which was fine with me because I wasn't either; his science fiction was, in the classic John Campbell mold, "here's a cool scientific idea; how would people react to it and use it?" The aforementioned The Gods Themselves, the Foundation trilogy (and prequels and sequels), The End of Eternity, the short story "Nightfall", and no doubt dozens more that I'm not thinking of right now, are all splendid examples of this.

Anyway, thank you, Isaac.

... killer brinicles freezing you instantly to death! (But only if you're a starfish or sea urchin, so it's OK.)

Seriously, cool video of an interesting scientific phenomenon.

Last night was chilly, so I made hot chocolate. Very simple recipe: heat a cup of whole milk, grate a bar of good dark chocolate, stir the latter into the former. I grated the chocolate using the "fine" side of the cowbell grater, into a plastic microwave dish (although a number of chocolate shavings ended up on the counter anyway). When I was finished and the milk hot, I picked up the dish -- and shavings started to levitate and dance, both off the dish and off the counter. It was a bit of a mess, but cool to watch....