Category: Astronomy

Luminous horned goat head surrounded by stars with one glowing red eye

A Mote in Capricorn’s Eye

On By rolcottIn Astronomy, Crazy Theories, UncategorizedLeave a comment

<bzzt, bzzt> “You again, Moire. What is it this time?”

“Better get over to my office, Walt. I’ve got some charts you’ll want to see, but you probably don’t want them spread all over.”

“Fifteen minutes. No, make that twenty. Bye.” <click>

Twenty minutes later on the dot, his cane taps my office doorpost. “Let’s see those charts.”

“Let me cast this video from Old Reliable to my wall screen. Watch it while I give you the background.”

Data from JPL’s Small Body Database

“I’ll need background to even read this thing.”

“I figured. Here’s a sketch for vocabulary. The big oval is a comet orbit, though they’re usually a lot skinnier than that, roughly ten times longer than wide. ‘Perihelion’ is Greek for ‘close to the Sun’. The word for its opposite point is ‘aphelion’. Your maybe‑incoming chunk of neutronium would be a quarter the Sun’s mass but far too small to see. Even so, I thought its gravity field could be enough to generate a signal made of long‑period comets kicked inward from the Oort cloud.”

“Ah, that’s why your chart’s doing aphelions. A comet at aphelion far from the Sun would be out in the Oort cloud and vulnerable to being kicked. Side‑to‑side in the chart is east‑west; up top is the Pole Star then down to the southern sky. So what you’re showing me is where in the sky each long‑term comet would be when it’s farthest from the Sun. The markers are pretty much everywhere each decade. What’s with the orange fringes?”

“They’re bar charts to summarize relative comet count in each 10‑degree slice of latitude or longitude. The biggest bar in each longitude set represents 4 comets; the biggest latitude bars represent 6. If comets are coming in randomly around the Equator, the summaries along the bottom would be essentially flat, like it shows for the 50 years starting in 1950.”

“This is the kind of map that stretches Greenland relative to Africa, isn’t it?”

“Mm-hm. The latitude lines are drawn parallel to each other although they actually converge on an spherical surface.”

“So I can correct for that by mentally squeezing distances between latitudes … I’d expect relatively few markers close to the poles compared to what’s near the Equator. Right, that’s roughly the latitude summary pattern given the small sample sizes. But what’s going on after 2010?”

“You noticed that red-dot cluster centered above the Equator at about –75°. It’s in the constellation Capricorn. I asked Old Reliable to select the group between –100° and –50° and chart where and when each comet was at its most recent aphelion. Here’s the result. By the way, the slope estimate is at the 75% confidence level. You don’t often see data as tight as that.”

“Whoa! Around 1100 A.D. something from beyond 200 a.u. in the general direction of Capricorn started knocking long‑period comets down from the Oort cloud. Every century that thing’s gotten 17 a.u. closer which gives us … about 400 years before planetary chaos breaks out. What’s an ‘a.u.’?

“Astronomical unit, essentially the radius of Earth’s orbit — 140 million kilometers. But here’s a plot of the same variables including all the long‑period comets reported since 1950. The red dots aren’t special; they behave like the general population. Feeling better?”

“Absolutely not. This looks like the entire Oort cloud is collapsing on us!”

“Relax. You’re looking at an observational artifact — a subtle one, the kind that scientists hate but they get their jollies from uncovering one. Especially if it’s someone else’s.”

“How is this an artifact? The dates and distances are right there.”

“The dates hide something deeper. We can’t see these guys at aphelion — they’re dark and far away. Our telescopes can only pick them up when they’re within 5 a.u. of the Sun, 10 a.u. at the most. Five a.u. is less than 3% of a 200‑a.u. orbit. Within a few percent, observation dates are perihelion dates in disguise. The chart’s horizontal axis is really perihelion‑to‑aphelion cycle time. We’ve known since Kepler’s time that more energetic comets fly farther and take longer to return.”

“Hmph. So your red dots are probably just a random eddy in the Oort cloud. Bye.”

~ Rich Olcott

Luminous horned goat head surrounded by stars with one glowing red eye

Neutronium Chill

On By rolcottIn Astronomy, Astronomy: Stellar Science, Crazy Theories, UncategorizedLeave a comment

<chirp, chirp> I recognize the caller’s number. “Afternoon, Walt. Weren’t you going to trash that phone?”

“Afternoon, Moire. I decided to keep it, just for you.”

“Aww.”

“Don’t get cute. My people have a follow-on question for you. The neutronium chunk that might or might not rearrange our Solar System — how much lead time do we have between when we detect it and when things go sour?”

“So many unknowns. The object’s size, its speed, what signal we’re monitoring, even what you mean by ‘go sour’.”

“Yes, yes, very uncertain. Make some assumptions.”

“Big assignment. I’ll start with size. The smallest neutron star we’ve ever seen is about 1.3 solar masses, but Oppenheimer’s calculations say smaller chunks could be stable. Suppose it’s near the theoretical minimum, say about a quarter of a solar mass, maybe 20‑25 kilometers in diameter.”

“A whole neutron star’s about that diameter. This chunk would be a small cast‑off.”

“No, the cast‑off could be wider than its parent. It’s only a fraction of the star’s mass, so there’d be less gravity squeezing its component particles together. Anyway, it’s a reasonable size for calculating the telescopic detection limit.”

“Walk me through that.”

“Sure. Our sharpest telescopes, the Hubble and the Webb, both use detectors that span about about 40 milliarcseconds per pixel‑width.”

” ‘Milli-‘ I get; that’s one one‑thousandth. ‘Arcseconds’?”

“Works like a clock. Sixty arcseconds to an arcminute, sixty arcminutes to a degree. While I’m at it, 360 degrees is full circle is 2π radians. Put it all together, one of those pixels covers about 0.2 microradian across the sky. Now visualize a triangle. One side spans the chunk; the angle opposite it is at Hubble’s detector.”

“A long, pointy triangle.”

“Pointy enough that the angle in radians is essentially equal to its sine and we can do trigonometry. Your question boils down to, how close does the chunk have to be so its light spans a Hubble pixel?” <keyboard clatter> “You’re not going to like this. A 20‑kilometer object casting a one‑pixel figure can’t be more than 180 million kilometers away. That’s already well inside the Solar System, closer to us than the Asteroid Belt. Just a one‑pixel ‘image,’ not a portrait, from our best telescope for visible light.”

“How about another part of the spectrum?”

“I wouldn’t bet on it. The chunk probably radiated X‑rays early on, but it’s had millions of years in interstellar space to cool off.”

“How is it millions? The Crab Nebula hosts a neutron star and its supernova looks pretty random to me. The Nebula could have flung a chunk at us and it’s only 6500 lightyears away.”

“The fastest interstellar traveler we’ve seen so far is 3I/Atlas, got here from who knows where with a base velocity of 58 kilometers per second. I’ll give you a factor of two — say the Crab flung your chunk at 120 km/sec. That’s still 2500 times slower than lightspeed. At that rate it’d take 16 million years to arrive here. The Crab supernova’s light got here only 970‑some years ago so no chance for an IR‑bright Crab chunk any time soon.”

“Neutrinos?”

“The IceCube Neutrino Observatory detects a million cosmic‑ray muons for every neutrino it sees. Tough odds.”

“Telescopic surveillance isn’t an option. Observing neutrinos is a crapshoot. How about gravitational messing with planet orbits?”

“Something subtler would appear first. Imagine a spherical shell where the inward pull of the Sun’s gravity just equals the outward pull of everything outside.”

“That’d be the outer edge of the Oort Cloud.”

Data from
wikipedia.org/wiki/List_of_long-period_comets

“Pretty much. The chunk will carry its own gravity sphere. Where the two spheres intersect, the opposing gravity fields fight. Some Oort objects fly outward, many drop inward to become long‑period comets. The chunk‑detection signal would be a drastic rise in long‑period comet sightings. Typical long‑period comets take hundreds of years to get down to where we can see them. Nonetheless, we’ve had an upward spike recently.”

“Because of improved technology?”

“Or improved financing. Congress is interested in finding Earth‑threatening asteroids. Look for asteroids, maybe find comets.”

“Lead time in centuries, opening bell may have rung. Bye”

Author’s conception of a neutronium fragment
being expelled from the Crab Nebula.

~ Rich Olcott

A Three Burdens Story

On By rolcottIn Astronomy: Stellar Science, Crazy Theories, Physics: Quantum Mechanics, UncategorizedLeave a comment

<bzzzt, bzzzt> “Who is this and how did you get this number?”

“Morning, Walt. It’s Sy Moire. Does hitting ‘Reply’ to your entry on my phone log count as spycraft?”

“Drat, another burner phone to trash. Oh well. Why the call?”

“Some history for your neutronium question, may make a difference.”

“Good difference or bad difference?”

“Depends on how you slant it, I suppose. The good news is that detecting that Earth‑threatening lump of neutronium would be easier than I thought. The bad news is that detecting it would be easier than I thought.”

“Forward and backward in the same statement. Unravel that.”

“It all goes back to Oppenheimer—”

“J Robert, the guy who ran the Manhattan Project?”

“The same, except before that he did theoretical Physics, not project management. Probably the most prominent physicist of the 1930s. He was active and influential in everything from molecular quantum mechanics and quantum field theory to astrophysics. He knew pretty much everyone who counted; everyone else knew of him. That made him a natural choice as a recruiter for the Project. I think many people were surprised when he turned out to be a good administrator.”

“Good for him and us. Why drag him into this?”

“He showed how neutron stars and black holes could happen. We’d known since 1915 that black holes were implicit in Einstein’s equations. Einstein himself didn’t think the Universe would allow matter to be that dense. In 1939 Oppenheimer showed how a star’s collapse could compress matter enough for the job. Actually, black holes were the easy part.”

“How could that be easy?”

“A star’s outer layers are supported by thermal pressure from the gas inside, right? When there’s not enough fuel to supply the heat, those outer layers come smashing inward like a roof when you knock out a load‑bearing wall. A big‑enough star would have plenty of gravitational potential energy to crush its core into black‑hole mode. Oppenheimer’s real challenge was explaining why the fall stopped partway for a smaller star. He used a tip from Fermi.”

“Enrico Fermi, the guy who built the nuclear reactor under the football field?”

“The same, except it wasn’t under the field, it was under the bleacher seats, but that’s another story. Anyway, Fermi had applied Pauli’s exclusion principle—”

“Out from the weeds, please.”

“Sorry. A couple of years prior, Fermi had worked out how a gas of quantum particles would behave under compression.”

“We’re talking electron or neutron gases?”

“Those among others. Squeeze a sparse quantum gas and measure the pressure it exerts at each decrease in volume. Pressure times volume is energy. For normal gases, pressure change times volume change at constant temperature is essentially constant. With quantum gases there’s a quantum‑limit pressure where the ΔP×ΔV energy goes nuts regardless of temperature. You need to input drastic amounts of energy to achieve even a small volume decrease. Technically, the limit’s called degeneracy pressure but I’d avoid that term in your report.”

“Because negative electron repels negative electron, naturally.”

“Nope, this is completely quantum, nothing to do with charge. It applies to neutrons just like it does to electrons although the limits are different. Try to cram too many quantum particles into a given volume and something has to give.”

“I see where you’re going. Does that energy limit depend on particle mass?”

“Indeed. Heavier particles have a higher limit.”

“Let me guess. White dwarf stars collapse to the electron limit, neutron stars to the neutron limit, pressure crushing beyond that makes a black hole. That’s what Oppenheimer calculated?”

“Mm‑hm. Better yet, he calculated minimum mass for each object type. That’s where the good‑news/bad‑news comes in. You need a lot of gravitational pressure to maintain a stable neutronium object. Below about a tenth of a solar mass, BLOOEY! If your nasty nova were to fling a too‑small chunk of neutronium at us, the chunk would disintegrate long before it could get this far.”

“So the good‑bad news is, a mass of neutronium could only get near us if it was more than a tenth of the Sun’s mass. Anything that heavy would make noticeable changes to planetary orbits long before we could see it. Bye.” <click>

~ Rich Olcott

Abstract cosmic composition with colorful swirling ribbons, organic forms, and stars

A Cosmic Trattoria

On By rolcottIn Astronomy: Multi-messenger, Crazy Theories, UncategorizedLeave a comment

Walt is not amused. ” ‘Not likely but probably’ — what kind of answer is that, Moire? You going for Pratchett’s ‘million-to-one chances crop up nine times out of ten’?”

“You asked me two questions, I gave you two answers. I won’t even bill you for one of them.”

“You know my opinion about lagniappes. We’ll pay for both, but only if we get value.”

“Your first question was, could a nova have flung a chunk of neutronium that’ll hit our Solar System?” <starts tapping on Old Reliable’s screen> “I assume your people are worried about protecting Earth.”

“I neither confirm nor deny that assumption.”

“Either way, by geometry alone the likelihood’s negligible. All our System’s planets and most of the satellites and asteroids and comets are within a few degrees of the Plane of the Ecliptic. Think of everything from Neptune’s orbit inward as a thin flat disk. From above, Earth’s cross‑section area is almost a trillionth of the disk’s area. Suppose your nova is 10 times as far away as our nearest star. Worst case is the nova hanging directly above the Ecliptic. Our disk would be a circular patch in the nova’s sky. If the nova throws a neutronium chunk, it can choose randomly from 20 billion patches the same size as ours; Earth is only a trillionth of one of them. Best case is the nova’s located edge-on to our disk; the odds of a hit would be far smaller. A neutronium chunk striking Earth is a framazillion times less likely than a hit from one of our own near‑Earth asteroids.”

“‘Framazillion.’ I’m going to quote you on that.”

“No extra charge. Now for your second question, whether we could detect a neutronium interloper. Yes, if we’re looking in the right direction with the right detectors.”

“Needs a full-sky survey, obviously, because we have no clue where it’s coming from. What kind of detectors? It’s got to be warmer than empty space. Infrared?”

“Mm-hm. The chunk’s free electrons would shine with black‑body radiation.at all wavelengths but IR’s your best choice.”

“Free electrons? I thought the thing was made of neutrons.”

“Sorry, that’s pop‑sci simplification. The neutrons in a neutronium object are stabilized by gravitational compression, but the gravity field tapers off near the surface. Deep inside you’ve got neutron soup, possibly superfluid, but the particles further up aren’t crowded quite as tightly and have ways of freezing up. There’s a slushy lower crust of nuclear pasta, then an atomic upper crust of iron and its transition‑metal relatives plus some hydrogen and helium. Finally there’s a free‑electron ‘atmosphere’.”

“Wait — nuclear pasta?”

“Technical term, believe it or not. Liquid water and ice make a slush, right, one ingredient occurring in two phases. Water has about 20 different phases—”

“Ice-nine, in Vonnegut’s book.”

“That’s a plot device, I’m talking real ice here. You get different ices at different temperatures and pressures because the microscopic‑level components re‑arrange. We think neutronium does the same. Near the top of a neutron star’s lower crust, the pressure’s low enough that neutrons and protons can clump together as monster nuclei with a high neutron/proton ratio. Theorists depict them as ‘gnocci‘ (or ‘meatballs’) floating in the uncrystallized neutron phase. Down below where the pressure’s higher, the gnocci phase breaks up to form long thin strands of ‘spaghetti.’ Even further down you get sheets of ‘lasagna’ and so on. Physicists can have fun, too. Anyway, IR detectors would be best because the star’s gravity field redshifts UV and visible black‑body emissions to longer wavelengths. But your problem is, that’s not neutronium‑specific.”

“Right, any warm rock would emit IR. Is there something else?”

“Yes, there is, and we already have the right observatories in place and operating.”

“What do they detect?”

“Neutrinos, the lightest particles we know of, about a millionth the mass of an electron. Every time a proton absorbs an electron and converts to a neutron, neutrinos are emitted. That happens a lot in neutronium; a chunk of it ought to be a bright neutrino source. We’ve got a dozen neutrino telescopes in operation all over the world. If they spot something, you’ll hear about it.”

“Bye.”

“Don’t mention it.”

Abstract cosmic composition with colorful swirling ribbons, organic forms, and stars

~ Rich Olcott

Rugged asteroid surrounded by glowing debris in a colorful nebula

Neutral Under Pressure

On By rolcottIn Astronomy: Stellar Science, Crazy Theories, Physics, UncategorizedLeave a comment

The Acme Building’s elevator takes me to the 12th floor with no hiccups, for a change. I unlock my office door and there’s “Walt,” standing in the middle of the room brandishing his cane with what looks like a fat cell phone plugged into it somehow. “The place is clean, Mr Moire. No listeners in the elevator shaft, corridor or office space, and I put temporary foam over your windows to block laser‑bounce sound pickup.”

“That’s good to know, Walt. Should I give you credit for fixing the elevator?”

“Not publicly. Found a dark web relay routine freeloading elevator’s controller computer. Disabled it so the machine can do its real job.”

“Nice work. But why so surreptitious? You know I don’t do military consults. And why come up to my office instead of meeting at Eddie‘s or the park as usual?”

“Tradecraft, Mr Moire — never use the same location too often. Espionage is a thing, military or not, and it doesn’t recognize national boundaries. My people have their secrets, too.”

“Naturally. What are your people curious about this time?”

“Neutronium.”

“Neutronium?”

“Yes, what can you tell me about it?”

“It’s really dense. You’ve heard the line that atoms are mostly empty space. An atomic nucleus is maybe a few femtometers across, but it floats in a ball of space that’s a thousand to ten thousand times wider. The space isn’t empty, of course — it’s occupied by spread‑out electronic charge. Neutronium doesn’t have that not‑quite‑empty space. A neutronium ball with the Sun’s mass would be a dozen kilometers across.”

“Mashed‑together charge like a metal. Would neutronium be shiny?”

“Possibly. I’ve never seen any.”

“Are there neutronium ores you could mine for?”

“Not on Earth, guaranteed. Except for the noble metals like gold, ore atoms are isolated from each other, dispersed in minerals like oxides or sulfides. Neutronium by its nature would have to be in a massive isolated deposit.”

“By its nature?”

“An isolated neutron lives about 15 minutes before it spits out an electron and becomes a proton. A neutron near enough to another nuclear particle is stabilized by the weak nuclear force, but that’s ineffective beyond a few femtometers. Either a neutron’s in an atomic nucleus or it’s mashed up against other neutrons in neutronium or it’s dead.”

“How about a chunk of neutronium buried in one of these ultra‑dense asteroids I’ve read about, like 33 Polyhymnia, or 16 Psyche that we’ve sent a space mission to look at?”

“You have read up, haven’t you? Not even those two asteroids are dense enough to host more than a speck of neutronium. Asteroid mass and volume are separate measurements; you need both to figure mass‑per‑volume density. Each component is a challenging exercise in accurate observation. The first guesstimate for Polyhymnia was that it was more than 10 times denser than iron. That’s why you’ve heard of it. With better data now we think both Polyhymnia and Psyche are at about the density of iron. Higher than most but too low for neutronium by a factor of quintillions.”

“Where else could we go for neutronium?”

“This’ll take some background. The more massive the star, the bigger its diameter and the longer it lives, right?”

Walt gives me a suspicious eye. “You’re fudging, Mr Moire.”

“Nothing gets past you, Walt. More massive stars burn hotter. The heat bulges them out, as you’d expect. The fudge is they exhaust their fuel faster so they die sooner. When the fuel gives out and they go nova, big guys collapse harder than smaller ones can. Their collapse squeezes their residual core tighter. Collapsing a really big star crams its remains into a volume smaller than its Schwartzschild radius. That makes a black hole. Smaller stars can’t go that far. The crush might stop when the residue’s electrons are squeezed into its atomic nuclei. Protons there could capture them and become neutrons. If so, you’ve got neutronium and a neutron star.”

“A nova’s pretty violent, shoots material out randomly?”

“One of the sloppiest, most violent events in the Universe.”

“Could a nova have flung a neutronium fragment through our Solar System like something flung ‘Oumuamua? Could we detect that?”

“Not likely but probably.”

Rugged asteroid surrounded by glowing debris in a colorful nebula

~ Rich Olcott

Nervous dog hiding in alley with police car sirens, fireworks, and crowd unrest

How Loud Can It Get?

On By rolcottIn Astronomy: Planetary Science, Physics: Waves, UncategorizedLeave a comment

Mr Richard Feder stumbles into Cal’s Coffee Shop with his hands over his ears. “Holy Pete, those fireworks were loud! They pulled out all the stops with that finale. BAM! BaBANG! BAMBAMBAM!! I’m still jazzed, see, I’m shaking. My dog back home’s hiding under the bed.”

Cal shoves a mug at him. “Try some of this.”

“Smells like a bakery. What is it?”

“It’s called chai. Just some spices and decaf tea. Supposed to be calming.”

<sips> “Hmm. … Yeah, seems to be working. Still can’t get over the impossible noise level, though. Had to be hundreds of decibels.”

I’m over here nursing my usual cup of mud. “Several hundred decibels can’t happen on Earth.”

“Hey, I was right there, I heard it, I felt it!”

“What you felt wasn’t sound, and it’s not measured in decibels.”

“Sounded like sound.”

<sketching on Old Reliable> “Sound is a continuous wave of out‑and‑in pressure changes, like the orange line here. The variation is what matters — push and pull, the waves average out to atmospheric pressure. What you felt was a shock front, a quick pulse of high pressure, all outward like the red line. OK, you felt a bunch of shock fronts, but not the regular waves that decibels care about.”

“What’s the green line about? It’s regular.”

“That stands as a baseline for comparisons. I’ve marked its high‑low range as pref. Most people doing sound measurements set pref to the smallest pressure swing that most people can hear, about 2×10-10 atmospheres—”

“That’s pretty small.”

“Indeed, but you’ve got to start somewhere. If you whisper to a partner at exactly that sound wave level, p=pref, the p/pref ratio is 1.0. That’s zero on the bel scale. Sounds from rustling leaves have a p/pref ratio about ten times larger. We give that a two‑bel rating. Every factor of ten above that rates an additional two bels. A busy nightclub could easily have a p/pref ratio near 105, ten bels, a hundred thousand times more pressure swing than your quiet whisper.”

“What’s that got to do with decibels?”

“They’re for rating sound waves that are between ten‑factors. ‘Deci-‘ means one‑tenth so there’s ten decibels per bel. The noise police would assess that ten‑bel nightclub at 100 decibels. If you sit right next to the loudspeakers where the sound pressure is 120 decibels, the extra 20 decibels pummel your eardrums with an extra ten times the pressure swing. Which is why people suffer short-term hearing loss at that intensity.”

“Uhhh… so 300 decibels from those fireworks would be a 1015 ratio which is a lot but why do you say it’s impossible?”

“That’s what the blue ‘Over‑driven’ line is about. Suppose you give an alarm siren a continuously growing power feed. As the siren’s power increases, it emits pressure peaks that push out more strongly and valleys that pull in more strongly. When the valley’s part of p eventually grows to atmospheric pressure patm, the sound’s pressure valleys try to drop below zero, which they can’t because zero is is a vacuum. Further output power beyond that level only goes to the outward pressure phase. The siren isn’t making a sound any more, it’s making push pulses. Maximum loudness happens when the p/pref ratio nears patm/pref. On Earth, patm/pref is 5×109. If you do the math, that’s 194 decibels. You just can’t make a sound any louder than that, no matter how you modify the siren.”

“You said ‘on Earth’ twice, like the limit’s different on other planets?”

“Sure. The same formula applies to any body with a solid surface and an atmosphere. The Solar System has only three planets and one moon that qualify. Here, I’ll tell Old Reliable to run the numbers for those. … How about that? Earth’s ‘loudest possible sound’ almost exactly matches the one for Saturn’s moon Titan. Mars is 40 decibels quieter than we are, but Venus is 40 decibels louder.”

“Dogs got sensitive ears. I bet they’d like it on Mars. They’d probably invent a different bel scale, though.”

Nervous dog hiding in alley with police car sirens, fireworks, and crowd unrest

~ Rich Olcott

Airborne Amazons

On By rolcottIn Astronomy: Planetary Science, UncategorizedLeave a comment

Vinnie blows into Cal’s place dripping wet. “Man, it’s coming down out there! This monsoon’s trying to drown us.”

“No monsoon, Vinnie, this rain’s from an atmospheric river.”

“Monsoon, river, what’s the difference, I’m soaked, Cathleen!”

“Cal, Vinnie needs a warm‑up mug, quick!”

“Comin’ right up. Here you go, Vinnie. Cathleen, I’ve always used ‘monsoon’ for rain like this. What’s wrong with that?”

“Because a proper monsoon is seasonal; the year’s too early for monsoon season around here.”

“Didn’t realize we had a monsoon season. I just figure if it’s not snowing and it’s not steaming we got rain.”

“Not funny, Vinnie. Our local weather deserves better from you. We have lots of sunny days even during our July‑September monsoon season.”

“Why pick on those particular months?”

“Temperature and wind patterns. Sy would push the ‘because’ all the way down to heat capacity difference. Per unit area, a one‑centimeter layer of rock has about ¾ the heat capacity of the same thickness of still water. Convective water circulation magnifies the difference by ten.”

“So?”

“So a given amount of energy will raise the temperature of a rock expanse almost 13 times as many degrees as it would the same ocean area. On the other hand, night‑time energy radiation cools rock by almost 13 degrees where the ocean would cool by one. Compared to the ocean, land surface gets hotter in the daytime, cools off more at night.”

“So?”

“So Summer sunlight heats land area more than its neighboring ocean. Air over warm land expands and rises, making room for water‑laden air from the relatively cool ocean cover. That air warms and rises, too, but as it rises it cools again. The water vapor condenses and rain falls. Come Autumn, land temperature drops more than ocean surface temperature does. That reverses the air’s general circulation and shuts off the rain. End of monsoon season.”

“It works that way all over the world?”

“Most everywhere except Antarctica. Apparently it stays so cold there all year around that the back‑and‑forth rocking never gets a chance to develop.”

“Doesn’t seem to have anything to do with the Coriolis Effect.”

“Most of the movement is roughly perpendicular to the local coastlines, but Coriolis gets into play farther away from the coast. The North American monsoon, for instance, comes up from the Gulf of California and trends northeast across the mountain states into Kansas and Oklahoma.”

Water vapor, afternoon of August 22, 2018. Dry air is orange.
Image from Albuquerque, NM National Weather Service

“That strong west‑to‑east trend looks like some weather maps I’ve used flown by. Is that an atmospheric river?”

“Similar, Vinnie, but no. Atmospheric rivers are a completely separate phenomenon from monsoons — different physical settings, different behavior. They’re both fueled by warm oceanic water vapor but that’s about it. Monsoons are seasonal, last for months, and hover over particular regions; atmospheric rivers are perennial, generally live for only a few days, and wander around. We’ve known about monsoons for millennia, but it wasn’t until 1992 that scientists had satellite data to support the rivers notion.”

“How can they be perennial and only last for days?”

“I meant that individual rivers come and go but the northern and southern hemispheres generally have about four each throughout the year. Rivers thousands of kilometers long, hundreds of kilometers wide, carrying as much water as the Amazon. Together they’re responsible for transporting 80‑90% of the tropical moisture that crosses the mid‑latitudes each year.”

“That’s a lot of water hanging over our heads. How could people have just missed them all those years?”

Vinnie has a calculating look. “A million square kilometers. How tall are these things?”

“Can’t give you a firm answer. Probably a kilometer or two but that’s a guess. The satellite sensors register total water mass from orbit down to ground. The numbers peak around 60 millimeters of H₂O per square centimeter. Spread along a one‑kilometer height that’s 60 g/m³ maximum; figure a 30‑gram average.”

“It’s just moist air, then, not liquid water. Cal, your breath’s more humid than that. A million cubic kilometers of 30‑gram 1‑meter cubes packs a lot of grams. I’m sure I’ve flown right through those things without noticing them.”

~ Rich Olcott

The Coriolis Mandala

On By rolcottIn Astronomy: Planetary Science, Physics: Newton and Gravity, UncategorizedLeave a comment

“Cathleen, this Coriolis Effect‘s rule is so easy. The force always twists you to the right no matter which way you travel. Going north, you swerve eastward; going south you swerve westward, always to the right. But what about the in‑betweens? What if I’m going east or west? Does the force just go away?”

“Of course not, Cal, but it mutates. Mind you, the rules you quoted only apply in Earth’s northern hemisphere. If you’re south of the Equator they go the other direction. Anyway, the northbound and southbound cases everybody writes about are the simplest to describe. You might be surprised how it varies across all the compass points separating them.” <pulling another image up on her tablet> “Here’s a chart I did for my class.”

“Whoa, that’s complicated.”

“Let me break it down for you. The circles around the outside represent different travel orientations — north’s at the top, then northeast to its left, directly east at the three-o’clock position, and so on. The brown arrows point to the corresponding direction. They’re all the same length to imply equal travel speed because why not.”

“Southbound’s at the bottom, just like on a map, right?”

“Right. Now, the blue arrow in a circle shows the relative Coriolis force experienced by an object traveling in that circle’s direction. See how the leftward force falls off from full‑strength if you’re northbound, to 70% if you’re going northeast, so zero for eastbound motion.”

“I’ll take your word for the 70%, but yeah, that’s what the picture shows. Wait, right after you turn the corner from east to south that blue arrow flips like the rule says.”

“It’s not like there’s a big toggle switch somewhere. If you’re going a little bit north of due east, there’s just a little bit of east‑pushing Coriolis; drive just a little bit south of due east there’s just a little bit of west‑pushing Coriolis. Build a Coriolis swerve‑meter. Swivel it all around the compass. It’ll show peak force when pointed north or south. The force smoothly fades away through zero, grows to a peak in the other direction, fades away, then re‑grows as you come back full circle.”

“So that’s what the pink and green disks are about, huh? Strong to fade‑away east both sides in the top half, strong to fade‑away west in the south?”

“You’ve got it.”

“What’s the red and blue stuff about then?”

“Re‑think the picture to 3‑D. Visualize each of those circles as a sphere. The thin black arrows are x‑y‑z pointers coming out from the sphere’s center. Can you see that?”

“The arrows coming out an angle, that’s like coming out of the screen?”

“Mm‑hm. Suppose you’re driving straight east in a vehicle that doesn’t care about gravity. What would happen?”

“Heh‑heh‑heh, lift‑off!”

“Exactly. It’s not centrifugal force, technically, but the Coriolis Effect’s equation establishes a trade‑off between Coriolis acting horizontally and a centrifuge‑like sibling acting vertically. Both sibs act to increase or decrease an object’s effective inertia depending on the object’s direction of motion relative to Earth’s rotation. The vertical component strengthens as the horizontal component weakens and vice‑versa.”

“The vertical one is the tubes coming out?”

“Yes, that’s what those are about. Long tubes in the diagram indicate high relative strength, short tubes signify weaker intensity, which is why the northbound and southbound spheres don’t have any tubes at all.” <grins> “Sy would appreciate my color choices.”

“I don’t get the joke.”

“Over there on the left side, the vertical component is upward, towards us. If a star’s coming towards its spectrum is shifted to shorter wavelengths, bluer than it it were standing still. No surprise, we call that a blue shift. Being an astronomer, I made those tubes blue‑ish.”

“I suppose the right side has red tubes because the vertical component pushes down when you’re westbound?”

“You broke the code, Cal. Red‑shifted stars are flying away from us. I’m being careful here — the red tubes don’t represent a true centripetal force. There’s no pushing and the effect doesn’t depend on distance from the rotation axis. But it makes a westbound truck act a bit like the road’s coming up to meet it.”

~ Rich Olcott

The Winds of Change

On By rolcottIn Astronomy: Planetary Science, Physics: Waves, Uncategorized1 Comment

“You said that so careful, Cathleen.”

“What that was that, Cal?”

“When you said those blue donuts in your diagram could be Earth’s equivalent to Jupiter’s brown bands. Why not the white zones, too?”

“Because Earth has a much better analog for the white zones. Juno‘s observations showed us Jupiter’s white zones floating a hundred or more kilometers above the brown stuff.”

“We don’t have that much room, do we?”

“Nowhere near. Our clouds and weather stay inside the troposphere, mostly less than a dozen kilometers up. Inside that shell, though, similar dynamics may apply.” <scribbling on her tablet> “Here’s a grossly oversimplified sketch.”

After an image by Kaidor, lic. under CC A-SA 3.0

“White frosting on the donuts?”

“Winds, Cal, not frosting, though they are cold. Think of each blue donut as a conveyor belt transporting air between warm and cold regions. The arrows reflect separate lower‑level and upper‑level wind regimes. What happens up at 60°N?”

“That’s actually a ring, right, goes all around the planet up there? I see two lower‑level conveyor belt donuts dumping at the same meridian — stuff’s gonna pile up over the ring unless the upper‑level parts move it out fast enough.”

“They do, mostly, during each hemisphere’s Summer. Winter’s another matter. The lower‑level conveyors are more sensitive to surface conditions than their upper‑level partners; seasonal surface condition changes affect the dump/clear balance. Wind speed’s driven by density difference; cold winter air is denser than summer air, even in the Arctic. Typical wintertime lower‑level polar cell transport dumps more air into that convergence than the upper‑level mechanism can sweep away.”

“So it piles up, like I said. Just sits there, I bet.”

“It might if the Earth weren’t rotating. That dense air acts to lift lighter air coming in from the South—”

“I know! Coriolis in action! The lighter southern air gets into the upper level first and it’s already turning to the east so it kicks that white cylinder into going east, too. Except it’s a ring.”

“It’s a continuous process so getting there first doesn’t count. But yes, eastward momentum from lighter southern air is the dominant influence that speeds the polar jet stream’s winds on their way, 200 kilometers/hour or more.”

“Whoa, that ‘polar jet stream’ phrase just sunk in. I keep hearing the weather guy talking about how the polar jet stream brings down the cold.”

“That’s like saying robins bring the springtime. The warm/cold front’s established by the balance between cold’s centrifugal force, heat’s poleward momentum and Coriolis twisting everything to the right. The jet stream just rides the back of the front. To my mind, it’s more accurate to say that the cold brings down the polar jet.”

“Cart before the horse.”

“Mm-hm. Remember I said that diagram is a gross simplification. One of the simplifications was to localize the stream at 60°N. Here’s a slightly less gross simplification. That ‘ring’ isn’t circular, it ranges more-or-less regularly between 60° and 45° in a nice pattern.”

“The crinkly circle looks like a coffee grinder part. So the cold just slides down that jet from Greenland to Europe.”

“Um, no. Weather doesn’t travel along the streams and the waves aren’t locked in place. The whole structure rotates eastward. Carl‑Gustaf Rossby discovered that, which is why it’s called a Rossby wave. Rossby was an early pioneer in atmospheric physics; his group’s weather predictions help decide World War II. Anyway, even Rossby waves are simplifications.”

“How much more unsimple can it be?”

“Much more. This idealized sketch shows how things might settle down under stable conditions. Conditions are rarely stable, especially now that global warming is upsetting the apple cart. The polar land areas are warming up the most, which means the polar cell’s outbound air currents are weaker and patchier than they used to be.”

“So the warm air masses can punch up closer to the poles like Summertime. Big deal.”

“Very big. Amplify the Rossby wave beyond a certain point, distortions create vortex cascades inside the peaks — the structure goes chaotic. Cold air leaks out past the warm air, like for this horrible early May snowstorm we’re getting.”

“Global warming causes cold air leaks. How about that?”

~ Rich Olcott

Belts And Zones

On By rolcottIn Astronomy: Planetary Science, Chemistry, Physics: Newton and Gravity, UncategorizedLeave a comment

“This cold-brew latte concoction — good choice, Cal. Thanks.”

“You’re welcome, Cathleen. Sounded like it’d fit your mood. Hey, Sy’s latitude racetracks got me wondering. Do Jupiter’s stripes follow the same pattern?”

“The ‘racetracks’ exist, sort of, but they’re a very small part of a very complicated picture. Jupiter’s belts and zones are each wider than Earth. Maybe half an Earth‑width deep, too. That’s just a small fraction of Jupiter’s fluid interior. A grand arena for a host of dueling pseudo‑forces.”

“Lotsa ways for winds to work, then.”

“Indeed. Ferocious drafts everywhere, up, down and sideways. Water in all its forms is a major weather driver here on Earth. Jupiter has water, too, in multiple forms acting at multiple atmospheric levels. It also has ammonia, sulfides, phosphines, tholins, hydrocarbons, a potpourri of chemicals flavoring its hydrogen and helium. Ammonia has gas/liquid and liquid/solid transitions like water does but they happen at their own temperatures and pressures. Jupiter’s white zones are mostly ammonia ice floating a couple hundred kilometers above its brown belts of ammonium sulfides and tholins. We’re still learning about how the planet’s complicated ammonia‑sulfides system works. Compared to Jupiter, Earth’s atmosphere is a kid’s toy.”

Earth’s landmasses in natural colors.
Image by Daniel R Strebe, licensed under CC A-SA 3.0

“Earth’s a lot smaller, for sure. Do we have belts and zones?”

“Oh, yes. You’ve seen evidence for them on a world map, but maybe you haven’t noticed it.” <pulls up an image on her tablet> “All those deserts stretching across low latitudes north and south of the forested Equator and below the boreal forests. Pretty distinctive pattern, right?”

“How about that? My astronomy magazines carry photos from Chile’s waterless Atacama observatories all the time. I’ve never connected those with the Australian outback or Namibia’s desert. All at the same level, aren’t they? And the Sahara’s tan blotch goes all the way east to the Gobi and matches northern Mexico and USA’s high plains on the other side. The green areas must get all the water that the deserts don’t. How does that square with your vapor‑ice water pump theory?”

“Sideways, actually. I don’t claim that molecules evaporating near the Equator make it all the way to an ice sheet in a single pass. The heat energy does, eventually, but the molecules get waylaid by the Coriolis force. That’s where the racetracks come in. I can’t do better than this graphic. Each of those flattened blue ovals is a slice through an air‑mass donut that dominates its latitude range.”

Earth’s atmospheric circulation patterns
After an image by Kaidor, lic. under CC A-SA 3.0

“That third‑down donut pretty much covers the Sahara. Is that why it’s dry?”

“It’s a big part of the reason, but you’re way ahead of me. Look at the colored arrows inside that donut’s slice on the right. Why do they point where they do?”

“Well, we’re hottest at the Equator. Hot air rises which is why the red arrow goes up. We said rising air over the ocean carries evaporated water with it, right, which the grey arrow will drop close by as the Earth spins eastward. That’s why the Equator’s got the forest. How’m I doin’?”

“Just fine. How about the yellow and orange arrows?”

“Um, the yellow’s colliding with the next donut north so it’s gotta go down?”

“There’s more to it than that. The air up high gets chilled which makes it more dense. That’s the major reason it descends. When it gets down to ground level, though, how much water does it hold?”

“Not much, ’cause it rained out over the Equator’s forests. The orange arrow’s gonna be thirsty so it’ll pick up more water sweeping over the ocean.”

“But what if it sweeps over land?”

“Ah‑hah. It’ll suck the land dry and THAT’s why the Sahara is where it is.”

“Right. Now, those black arrows over the same cell…?”

“Northbound twisting to the right — that’s Coriolis in action. The gray arrow up top must skew eastward. By the rules, the southbound orange arrow at sea level skews west. Hey, that’s those white‑arrow trade winds. Cool.”

“Those blue donuts could be Earth’s version of Jupiter’s brown belts.”

~ Rich Olcott