The Buck Rolls On, We Hope

<knock, knock> “Door’s open. Come in but maintain social distance.”

“Hiya, Sy. Here’s your pizza, still hot and everything but no pineapple.”

“Thanks, Eddie. Just put it on the credenza. There’s a twenty there waiting for you. Put the balance on my tab.”

“Whoa, I recognize this bill. It’s the one that Vinnie won off me at the after‑hours dice game last month before all this started. See, I initialed it down here on the corner ’cause Vinnie usually don’t do that well. How’d you get it from him?”

“I didn’t get it from Vinnie, I got it from Al when I sold him a batch of old astronomy magazines. Vinnie must have finally paid off his tab at Al’s coffee shop.”

“Funny how that one bill just went in a circle. Financed some risky business, paid off a loan, bought stuff, and here I get it again so I can buy stuff to make more pizza. That’s a lotta work for one piece of paper.”

“Mm-hm. Everyone’s $20 better off now, all because the bill kept moving. Chalk it off to ‘the velocity of money.‘ If Vinnie didn’t spend that money the velocity’d be zero and none of the rest would have happened.”

“That sounds suspiciously like Physics, Sy.”

“Guilty as charged, Eddie. Just following along with what Isaac Newton started back when he was staying at his mother’s place, hiding out from the bubonic plague.”

Newton, after a day at the beach
while wearing an anti-viral mask

“What’s that got to do with money? Was Newton a banker?”

“Not quite, although the last 30 years of his life he headed up England’s Royal Mint. The core of his work during his Science years was all about change and rate of change. His Laws of Motion quantified what it takes to cause change. He developed his version of calculus to bridge between how fast change happens and how much change has happened.”

“Hey, that’s those graphs you showed me, with the wave on the top line and the slope underneath.”

“Bingo. Pandemics are a long way from the simple systems that Newton studied, but the important point is that to study his planets and pendulums he developed general strategies for tackling complex situations. He started with just a few basic concepts, like position and speed, and expanded on them.”

“Speed’s speed, what’s to expand?”

“Newton expanded the notion of speed to velocity, which also includes direction. From Newton’s point of view, the velocity of a planet in orbit is continuously changing even if its miles per hour is as steady as … a planet.”

“Who cares?”

“Newton did, because he wanted to know what makes the change happen. His starting point was if there’s any motion, it’s got to be at constant speed and in a straight line unless some force causes a velocity change. That’s where his notion of gravity came from — he invented the idea of ‘the force of gravity‘ to account for us not flying off the rotating Earth and the Earth not zooming away from the Sun. His methods set the model that physicists have followed ever since — if we see motion, we measure how fast it’s happening and then we look for the force or forces that can explain that.”

“Now I see where you’re going. That ‘velocity of money‘ thing is about how fast the paper changes hands, isn’t it? Wait, if Vinnie had put that twenty up on his wall as a trophy, then the chain would’ve been broken.”

“Right, or if Al had diverted it to buy, say, coffee beans. That’s why we say velocity of money and not speed, because the direction of flow counts.”

“Smelling more and more like Physics, Sy. Like, there’s astrophysics and biophysics and you’re coming up with econophysics.”

“Well, yeah, but I didn’t invent the term. It’s already out there, with textbooks and academic study groups and everything. It’s just interesting to use economics as a metaphor for physics and vice-versa. The fun is in seeing where the metaphors break down.”

“I see one already, Sy. Those forces — we all had different reasons to kick the bill along.”

“Good point. Now we figure out those forces.”

~~ Rich Olcott

Shortfall

<chirp, chirp> The non-business line again. “Moire here.”

“Hiya, Sy, it’s Eddie. I’m taking orders for tonight’s deliveries. I got some nice-looking artichokes here, how about a garlic and artichoke pizza?”

“No thanks, Eddie, I’ll stick with my usual pepperoni. Wait, you got any ham?”

“Sure.”

“Let’s go with a Hawai’ian.”

“Sy, we’ve had this conversation. You want pineapple on pizza you open a can and dump some on there after I leave the premises and don’t tell me. I got standards!”

“Calm down, Eddie, just yanking your chain. Yeah, do me one of those garlic and artichoke ones. Sounds more classical.”

“That’s better. I got you in the 6:15 wave, OK? Hey, that reminds me. I read your post series about waves and that got me thinking.”

“Nice to know someone reads them.”

“Well, things are real quiet, just me in the kitchen these days so I’m scraping the barrel, you know?”

“Ouch.”

“Gotcha back. Anyhow, that series was all about wiggly waves that repeat regular-like, right? I get that scientists like ’em ’cause they’re easy to calculate with. But that Logic Curve you wrote about goes up and doesn’t come back down again. Does anybody do math with that kind?”

Logistic Curve — blue line,
Associated slope — red line

“Logistic Curve. ‘Logic Curve‘ isn’t a thing. The mathematicians have come up with a plethora of curves and curve families. The physicists have found uses for many of them. The Logistic Curve, for instance, is one of the first tools they take off the shelf for systems that have both lower and upper limits. You’ve seen a lot about how it’s applied to epidemiology. People also use it for ecology, economics, linguistics, chemistry, even agriculture.”

“What do the top and bottom lines have to do with each other?”

“Ah. Sorry I hadn’t made that clear. OK, find a blank page in your order pad. At the top draw a horizontal zig-zag line like a series of 45‑degree triangles touching corners.”

“45 degrees is easy — that’s an 8-slice pizza. Done.”

“You’ve just drawn what’s called a triangle wave, no surprise. OK, now right under that, you’re going to draw another wave that shows the slope of each triangle segment. Where the triangle line goes up you’ve got a positive slope that goes up one unit for every unit across so draw a line at plus‑one, OK?”

“A-ha. Got it.”

“Where the triangle line goes down you’ve got a negative slope, minus‑one.”

“What about where the triangles got points?”

“Just draw a vertical line to connect the slope segments. What’s the completed second line look like?”

“A zig-zag bunch of square boxes. Hey, wait, we made the second line be the slopes for all the pieces, right? Lemme go check the picture in the ‘Curve‘ post. So what you’re saying is … the red line is all the slopes along the blue line … OK, can I say that the red line is how fast stuff is coming at me and the blue line is the backlog?”

“Half-right. For what we’re talking about, ‘slope‘ is whatevers per time‑unit. The blue line shows how much total has come at you so far. Backlog is a little more complicated.”

“I gotta go back and read those posts again. Now I see why they’re saying ‘flattening the curve‘ — they want the blue line to not climb so fast.”

“That’s part of it.. Flattening that red-line curve as much as we can is important. That’s what the masks and social distancing are about. Maybe as many people get sick, total, but if they trickle in instead of flooding in then they don’t overload the system. Here, I’ll send a sketch to your phone.”

“Got it, but there’s lots of lines there.”

“The red line is your completion rate — pizza orders per hour, patients per day, whatever. The red line goes flat because having only one oven limits your throughput. The gray part above it is pizzas per hour you couldn’t bake or patients your hospital couldn’t take that day. The green line is doable business; the black line shows how more capacity would have improved things.”

“Reduce the incoming, raise the capacity or lose the people. Whoa.”

~~ Rich Olcott

Flattening The Curve

<chirp chirp> My phone’s non-business ring-tone. “Moire here.”

“Hi, Mr Moire, it’s me, Jeremy, again. Sorry for the hold-up. My phone’s on the charger now so we can keep going about the Logistics Curve and all.”

“Logistic Curve, Jeremy, singular. Logistics plural has to do with managing the details of a military or business operation. That’s quite different from population growth which is what the Logistic Curve is about. Though come to think of it, these days we’re seeing a tie‑in. So where were we?”

“We had that S-shaped Logistic Curve with exponential growth at the beginning but then it plateaus and you showed me a humpy curve that’s the slope of the other one and you said the humpy curve is like R = K*S*(N‑S) if N is everybody and S is how many are susceptible to the virus. But you kind of skipped over K.”

“True and I’ll get to K, but that ‘humpy’ curve is important. In the context of the pandemic, it’s people per day — how many catch the virus, how many show up for medical care, how many need ventilators or even mortuary care — there’s a different K for each question. The hump is what we’re trying to get control of. The K factors summarize a whole pipeline of ifs and maybes. Some of them are knobs that we may be able to use to flatten the hump.”

“We can do that? How?”

“Good question. Here, let me send your phone another image. Let me know when you receive it.”

“It’s here, Mr Moire. Looks like you’ve got three Logistic Curves but they’re stretched out different amounts.”

“Stretched out on the time axis, and that’s crucial. I generated those three plots by using different values for K. Sooner or later in all three models everyone catches the bug. In the blue-line case, though, that happens over a much longer time interval than in the red-line case. If you’re a public health official or hospital administrator you pray for the blue-line case — the slow initial rise gives you a heads-up and more time to get ready for future incoming cases. Better yet, because the cases-per-day peak is flatter you don’t need as many masks and ventilators to take of the patients and your front-line people are less likely to be over‑extended. Assuming you’ve hired enough in the first place.”

“So the government wants to reduce the K numbers to get to the blue-line case.”

“Absolutely. Keep in mind, K is such a complicated summary of things that realistic models are complex. Experienced modelers know that the more factors you put into a model, the riskier the predictions become. Anyway some of the things that go into K we can’t control, we can only measure or estimate them and try to account for what’d happen if something changes.”

“Like what?”

“Suppose you’re exposed to the virus. What’s the probability that you’ll come down with symptoms bad enough to need medical care? Current data suggests those odds depend a lot on uncontrollable things like your age and medical history. A model for a retirement community almost certainly needs a different set of K-values then a model for a college town full of teens and twenty-somethings. But that gets into a different cluster of factors.”

“That’s for sure. My grandparents are a lot more careful about their health than my crew is.”

“Which gets us into the K-factors we can at least try to manage. Simple example — you can’t catch the virus if you’re not exposed to it. That’s what Social Distancing is all about and that’s why you’re staying at home, thank you very much. Typically, models gauge that piece by surveying what fraction of the population is complying with the stay-at-home, masking and 6-feet-away rules. We need to get to 70% or better to keep the patients-per-day rate down to what the hospitals can cope with. A vaccine, when we get one, will have the same effect but that’s a year away.”

“Yeah, and if someone invents a good treatment so people don’t have to go on ventilators, that’d help the K for that end of the pipeline.”

“Get to work on it, Jeremy.”

~~ Rich Olcott

The Curve To Be Flattened

<chirp chirp> My phone’s ring-tone for an non-business call. “Moire here.”

“Mr Moire, it’s Jeremy.”

“I hope so, Jeremy, my phone shows your caller-ID. I’m glad you called instead of trying to drop by, the city being under lockdown orders and all. What’s your question?”

“Oh, no question, sir, I just called to chat. It’s lonely over here. If you’ve got the time, anything you’d like to talk about would be fine.”

“Mm… Well, I am working on a project but maybe talking it out will help get my thoughts in order. Have you seen that ‘Flatten the curve‘ chart?”

“Sure, it’s been hard to escape. They use it to tell us why we shouldn’t do group stuff while this virus is going around. Are you writing about where the chart comes from?”

“That’s my project, all right. There’re two ways to get to that chart and I’m trying to decide which will work better. I could start from ecology studies of invading organisms taking over a new territory. At first the organisms multiply rapidly, doubling then doubling again —”

“That’s exponential growth, Mr Moire. We talked about that!”

“Just sent you an image. When researchers plot invasions they usually look like the black line, the Logistic Curve. Its height represents the organism’s population as time increases left-to-right. At the beginning there’s that exponential rise. Over on the right the growth rate slows as the plants or animals or bugs use up increasingly scarce resources. The part in the middle’s almost linear. All that’s a familiar story by now, right?”

The Logistic Curve (black) and its slope (red)

“Uh-huh. We talked a lot about ecology back in kid school except we hadn’t learned graphs yet. What’s the red curve?”

“That’s the interesting part I’m trying to write about. One way to look at it is that it’s simply the slope of the Logistic curve. See how where the Logistic is rising, the slope is rising, too? That’s the way exponentials work — ‘the higher the faster‘ as they say. The slope switches direction just where the Logistic switches from growth to slow-down. The Logistic Curve approaches its limit when the organism’s population approaches the carrying capacity of the territory. That’s also where the slope gets shallowest. Very few resources, very little expansion.”

“What’s the other way to look at it?”

“We start with the slope curve itself. It has its own straight-forward interpretation, especially if the organism is a a bacterium or virus that causes disease. Consider the population under attack as the resource. How fast will the disease spread?”

“Uh… what I keep hearing is that if more people get sick, other people will get infected faster.”

“But what happens when nearly everyone’s caught it and they’ve either recovered or left us?”

“Oh, there’ll be fewer people left to catch it so the disease spreads more slowly.”

“Let me put that into algebra. I’ll write N for the total number of people and that’ll be a constant, we hope. At any given time we’ve got S as the current number of people who are susceptible. Then (N‑S) tells us how many people are NOT susceptible. Are you with me?”

“Fine so far.”

“So from what we’ve just said, the rate of infection is low when S is low and also low when (N‑S) is low. One way to make that into an equation is to write the rate as R = K*S*(N‑S). K is just a number we can adjust to account for things like virulence and Social Distance effectiveness. If we plot R against time what shape will it have?”

“Mmm… S is nearly the same as N at the start so (N‑S) is nearly zero then. At the finish, S is nearly zero. Exactly in the middle S equals (N‑S). They each have to be higher than near-zero there. That makes R be low at each end and high in the middle. Ah, that’s sort-of the shape of the slope curve!”

“It’s exactly the shape of the slope curve. So how do we flatten it?”

<click-click, click-click> “Oops, Mr Moire, my phone battery’s about dead. Gotta go get the charger. I’ll be right back.”

“I’ll be here, Jeremy.”

~~ Rich Olcott

Sisyphus on A Sand Dune

I’m walking the park’s paths on a lovely early Spring day when, “There you are, Moire. I got a question!”

“As you always do, Mr Feder. What’s your question this time?”

“OK, this guy’s saying that life is all about fighting entropy but entropy always increases anyway. I seen nothing in the news about us fighting entropy so where’s he get that? Why even bother if we’re gonna lose anyway? Where’s it coming from? Can we plug the holes?”

“That’s 4½ questions with a lot of other stuff hiding behind them. You’re going to owe me pizza at Eddie’s AND a double-dip gelato.”

“You drive a hard bargain, Moire, but you’re on.”

“Deal. Let’s start by clearing away some underbrush. You seem to have the idea that entropy’s a thing, like water, that it flows around and somehow seeps into our Universe. None of that’s true.”

“That makes no sense. How can what we’ve got here increase if it doesn’t come from somewhere?”

“Ah, I see the problem — conservation. Physicists say there are two kinds of quantities in the Universe — conserved and non‑conserved. The number of cards in a deck is is a conserved quantity because it’s always 52, right?”

“Unless you’re in a game with Eddie.”

“You’ve learned that lesson, too, eh? With Eddie the system’s not closed because he occasionally adds or removes a card. Unless we catch him at it and that’s when the shouting starts. So — cards are non-conserved if Eddie’s in the game. Anyway, energy’s a conserved quantity. We can change energy from one form to another but we can’t create or extinguish energy, OK?”

“I heard about that. Sure would be nice if we could, though — electricity outta nothing would save the planet.”

“It would certainly help, and so would making discarded plastic just disappear. Unfortunately, mass is another conserved quantity unless you’re doing subatomic stuff. Physicists have searched for other conserved quantities because they make calculations simpler. Momentum‘s one, if you’re careful how you define it. There’s about a dozen more. The mass of water coming out of a pipe exactly matches the mass that went in.”

“What if the pipe leaks?”

“Doesn’t matter where the water comes out. If you measure the leaked mass and the mass at the pipe’s designed exit point the total outflow equals the inflow. But that gets me to the next bit of underbrush. Energy’s conserved, that’s one of our bedrock rules, but energy always leaks and that’s another bedrock rule. The same rule also says that matter always breaks into smaller pieces if you give it a chance though that’s harder to calculate. We measure both leakages as entropy. Wherever you look, any process that converts energy or matter from one form to another diverts some fraction into bits of matter in random motion and that’s an increase of entropy. One kind of entropy, anyway.”

“Fine, but what’s all this got to do with life?”

“It’s all to get us to where we can talk about entropy in context. You’re alive, right?”

“Last I looked.”

“Ever break a bone?”

<taps his arm> “Sure, hasn’t everybody one time or another?”

“Healed up pretty well, I see. Congratulations. Right after the break that arm could have gone in lots of directions it’s not supposed to — a high entropy situation. So you wore a cast while your bone cells worked hard to knit you together again and lower that entropy. Meanwhile, the rest of your body kept those cells supplied with energy and swept away waste products. You see my point?”

“So what you’re saying is that mending a broken part uses up energy and creates entropy somewhere even though the broken part is less random. I got that.”

“Oh, it goes deeper than that. If you could tag one molecule inside a living cell you’d see it bouncing all over the place until it happens to move where something grabs it to do something useful. Entropy pushes towards chaos, but the cell’s pattern of organized activity keeps chaos in check. Like picnicking on a windy day — only constant vigilance maintains order. That’s the battle.”

“Hey, lookit, Eddie’s ain’t open. I’ll owe you.”

“Pizza AND double-dip gelato.”

~~ Rich Olcott

Presbyopic Astronomy

Her phone call done, Cathleen returns to the Spitzer Memorial Symposium microphone with her face all happiness. “Good news! Jim, the grant came through. Your computer time and telescope access are funded. Woo-hoo!!”

<applause across the audience and Jim grins and blushes>

Cathleen still owns the mic. “So I need to finish up this overview of Spitzer highlights. Where was I?”

Maybe-an-Art-major tries to help. “The middle ground of our Universe.”

“Ah yes, thanks. So we’ve looked at close-by stars but Spitzer showed us a few more surprises lurking in the Milky Way. This, for instance — most of the image is colorized from the infra‑red, but if you look close you can see Chandra‘s X‑ray view, colorized purple to highlight young stars.”

The Cepheus-B molecular cloud
X-ray: NASA/CXC/PSU/K. Getman et al.; IRL NASA/JPL-Caltech/CfA/J. Wang et al

<hushed general “oooo” from the audience>

“Giant molecular clouds like this are scattered throughout the Milky Way, mostly in the galaxy’s spiral arms. As you see, this cloud’s not uniform, it has clumps and voids. By Earth standards the cloud is still a pretty good vacuum. The clumps are about 10-15 of our atmosphere’s density, but that’s still a million times more dense than our Solar System’s interplanetary space. The clumps appear to be where new stars are born. The photons and other particles from a newly-lit star drive the surrounding dust away. My arrow points to one star with a particularly nice example of that — see the C-shape around the star?”

The maybe-an-Art-major pipes up. “How about that one just a little below center?”

“Uh-huh. There’s so much activity in that dense region that the separate shockwaves collide to create hot spots that’ll generate even more stars in the future. The clouds are mostly held together by their own gravity. They last for tens of millions of years, so we think of them as huge roiling stellar nurseries.”

“Like my kid’s day care center but bigger.”

“Mm-mm, but let’s turn to the Milky Way’s center, home of that famous black hole with the mass of four million Suns and this remarkable structure, a double-helix of warm dust.”

False-color infra-red image of the Double-Helix Nebula
The double helix nebula.
Credit: NASA/JPL-Caltech/M. Morris (UCLA)

Vinnie blurts out, “That’s a jet from a black hole! One of Newt’s babies.”

Newt can’t resist breaking into Cathleen’s pitch. “Maybe it’s a jet, Vinnie. Yes, it’s above the central galactic plane and perpendicular to it, but the helix doesn’t quite point to the central black hole.”

“So take another picture that follows it down.”

“We’d love to, but we can’t. Yet. That image came from a long-wavelength instrument that only operated during Spitzer‘s initial 5-year cold period. Believe me, there are bunches of astronomers who can’t wait for the James Webb Space Telescope‘s far-IR instruments to get into position and start doing science. Meanwhile, we’ve got just the one image and a few earlier ones from an even less-capable spacecraft. This thing may be a lit-up part of a longer structure that twists down to the black hole or at least its accretion disk. We just don’t know.”

Cathleen takes control again. “The next image comes from outside our galaxy — far outside.”

Spitzer visualization of Galaxy MACS 1149-JD1
Credit: NASA/ESA/STScI/W. Zheng (JHU), and the CLASH team

The maybe-an-Art-major snorts, “Pointillism derivative!”

“No, it’s pixels from a starfield image with a very low signal-to-noise ratio. That red blotch in the center is one of the most distant objects ever observed, gracefully named MACS 1149-JD1. It’s a galaxy 13.2 billion lightyears away. That’s so far away that the expansion of the Universe has stretched the galaxy’s emitted photons by a factor of 10.2. Spectrum-wise, 1149-JD1’s ultra-violet light skipped right past the visible range and down into the near infra-red. Intensity-wise, that galaxy’s about 5200 times further away than the Andromeda galaxy. Assuming the two are about the same overall brightness, 1149-JD1 would be about 27 million times fainter than Andromeda.”

“How can we even see anything that dim?”

“We couldn’t, except for a fortunate coincidence. Right in line between us and 1149-JD1 there’s a massive galaxy cluster whose gravity acts like a lens to focus 1149-JD1’s light.”

The seminar’s final words, from maybe-an-Art-major — “A distant light, indeed.”

~~ Rich Olcott

Myopic Astronomy

Cathleen goes into full-on professor mode. “OK folks, settle down for the final portion of “IR, Spitzer and The Universe,” our memorial symposium for the Spitzer Space Telescope which NASA retired on January 30. Jim’s brought us up to speed about what infra-red is and how we work with it. Newt’s given us background on the Spitzer and its fellow Great Observatories. Now it’s my turn to show some of what Astronomy has learned from Spitzer. Thousands of papers have been published from Spitzer data so I’ll just skim a few highlights, from the Solar System, the Milky Way, and the cosmological distance.”

“Ah, Chinese landscape perspective,” murmurs the maybe-an-Art-major.

“Care to expand on that?” Cathleen’s a seasoned teacher, knows how to maintain audience engagement by accepting interruptions and then using them to further her her own presentation.

“You show detail views of the foreground, the middle distance and the far distance, maybe with clouds or something separating them to emphasize the in‑between gaps.”

“Yes, that’s my plan. Astronomically, the foreground would be the asteroids that come closer to the Earth than the Moon does. Typically they reflect about as much light as charcoal so our visible-light telescopes mostly can’t find them. But even though asteroids are as cold as interplanetary space that’s still above absolute zero. The objects glow with infra-red light that Spitzer was designed to see. It found hundreds of Near-Earth Objects as small as 6 meters across. That data helped spark disaster movies and even official conversations about defending us from asteroid collisions.”

<A clique in the back of the room> “Hoo-ahh, Space Force!

Some interruptions she doesn’t accept. “Pipe down back there! Right, so further out in the Solar System, Spitzer‘s ability to detect glowing dust was key to discovering a weird new ring around Saturn. Thanks to centuries of visible‑range telescope work, everyone knows the picture of Saturn and its ring system. The rings together form an annulus, an extremely thin circular disk with a big round hole in the middle. The annulus is bright because it’s mostly made of ice particles. The annulus rotates to match Saturn’s spin. The planet’s rotational axis and the annulus are both tilted by about 27° relative to Saturn’s orbit. None of that applies to what Spitzer found.”

Vinnie’s voice rings out. “It’s made of dust instead of ice, right ?”

Cathleen recognizes that voice. “Good shot, Vinnie, but the differences don’t stop there. The dust ring is less a disk than a doughnut, about 200 thousand times thicker than the icy rings and about 125 times wider than the outermost ice ring. But the weirdest part is that the doughnut rotates opposite to the planet and it’s in Saturn’s orbital plane, not tilted to it. It’s like the formation’s only accidentally related to Saturn. In fact, we believe that the doughnut and its companion moon Phoebe came late to Saturn from somewhere else.”

She takes a moment for a sip of coffee. “Now for the middle distance, which for our purpose is the stars of the Milky Way. Spitzer snared a few headliners out there, like TRAPPIST-1, that star with seven planets going around it. Visible-range brightness monitoring suggested there was a solar system there but Spitzer actually detected light from individual planets. Then there’s Tabby’s Star with its weird dimming patterns. Spitzer tracked the star’s infra‑red radiance while NASA’s Swift Observatory tracked the star’s emissions in the ultra‑violet range. The dimming percentages didn’t match, which ruled out darkening due to something opaque like an alien construction project. Thanks to Spitzer we’re pretty sure the variation’s just patchy dust clouds.”

Spitzer view of the Trifid Nebula
Credit: NASA/JPL-Caltech/J. Rho (SSC/Caltech)

<from the crowd in general> “Awww.”

“I know, right? Anyway, Spitzer‘s real specialty is inspecting warm dust, so no surprise, it found lots of baby stars embedded in their dusty matrix. Here’s an example. This image contains 30 massive stars and about 120 smaller ones. Each one has grown by eating the dust in its immediate vicinity and having lit up it’s now blowing a bubble in the adjacent dust.” <suddenly her cellphone rings> “Oh, sorry, this is a call I’ve got to take. Talk among yourselves, I’ll be right back.”

~~ Rich Olcott

The Fourth Brother’s Quest

Newt Barnes is an informed and enthusiastic speaker in Cathleen’s “IR, Spitzer and the Universe” memorial symposium. Unfortunately Al interrupts him by bustling in to refresh the coffee urn.

After the noise subsides, Newt picks up his story. “As I was saying, it’s time for the Spitzer‘s inspirational life story. Mind you, Spitzer was designed to inspect very faint infra-red sources, which means that it looks at heat, which means that its telescope and all of its instruments have to be kept cold. Very cold. At lift-off time, Spitzer was loaded with 360 liters of liquid helium coolant, enough to keep it below five Kelvins for 2½ years.”

“Kelvins?”

“Absolute temperature. That’d be -268°C or -450°F. Very cold. The good news was that clever NASA engineers managed to stretch that coolant supply an extra 2½ years so Spitzer gave us more than five years of full-spectrum IR data.”

<mild applause>

“Running out of coolant would have been the end for Spitzer, except it really marked a mid-life transition. Even without the liquid helium, Spitzer is far enough from Earth’s heat that the engineers could use the craft’s solar arrays as a built-in sunshield. That kept everything down to about 30 Kelvins. Too warm for Spitzer‘s long-wavelength instruments but not too warm for its two cameras that handle near infra-red. They chugged along just fine for another eleven years and a fraction. During its 17-year life Spitzer produced pictures like this shot of a star-forming region in the constellation Aquila…”

NASA/JPL-Caltech/Milky Way Project.

The maybe-an-Art-major goes nuts, you can’t even make out the words, but Newt barrels on. “Here’s where I let you in on a secret. The image covers an area about twice as wide as the Moon so you shouldn’t need a telescope to spot it in our Summertime sky. However, even on a good night you won’t see anything like this and there are several reasons why. First, the light’s very faint. Each of those color-dense regions represents a collection of hundreds or thousands of young stars. They give off tons of visible light but nearly all of that is blocked by their dusty environment. Our nervous system’s timescale just isn’t designed for capturing really faint images. Your eye acts on photons it collects during the past tenth of a second or so. An astronomical sensor can focus on a target for minutes or hours while it accumulates enough photons for an image of this quality.”

“But you told us that Spitzer can see through dust.”

“That it can, but not in visible colors. Spitzer‘s cameras ignored the visible range. Instead, they gathered the incoming infrared light and separated it into three wavelength bands. Let’s call them long, medium and short. In effect, Spitzer gave us three separate black-and-white photos, one for each band. Back here on Earth, the post-processing team colorcoded each of those photos — red for long, green for medium and blue for short. Then they laid the three on top of each other to produce the final image. It’s what’s called ‘a falsecolor image’ and it can be very informative if you know what to look for. Most published astronomical images are in fact enhanced or colorcoded like this in some way to highlight structure or indicate chemical composition or temperature.”

“What happened after the extra extra years?”

“Problems had just built up. Spitzer doesn’t orbit the Earth, it orbits the Sun a little bit slower than Earth does. It gets further away from us every minute. It used to be able to send us its data almost real-time, but now it’s so far away a 2hour squirt-cast drains its batteries. Recharging the batteries using Spitzer‘s solar arrays tilts the craft’s antenna away from Earth — not good. Spitzer‘s about 120° behind Earth now and there’ll come a time when it’ll be behind the Sun from us, completely out of communication. Meanwhile back on Earth, the people and resources devoted to Spitzer will be needed to run the James Webb Space Telescope. NASA decided that January 30 was time to pull the plug.”

Cathleen takes the mic. “Euge, serve bone et fidélis. Well done, thou good and faithful servant.”

~~ Rich Olcott

A Tale of Four Brothers

Jim hands the mic to Cathleen, who announces, “Bio-break time. Please be back here in 15 minutes for the next speaker. Al will have fresh coffee and scones for us.” <a quarter-hour later> “Welcome back, everyone, to the next session of our ‘IR, Spitzer and the Universe‘ memorial symposium. Our next speaker will turn our focus to the Spitzer Space Telescope itself. Newt?”

“Thanks, Cathleen. Let’s start with a portrait of Spitzer. I’m putting this up because Spitzer‘s general configuration would fit all four of NASA’s Great Observatories…

A NASA artist’s impression of Spitzer against an IR view of the Milky Way’s dust

“Each of them was designed to be carried into space by one of NASA’s space shuttles so they had to fit into a shuttle’s cargo bay — a cylinder sixty feet long and fifteen feet in diameter. Knock off a foot or so each way to allow for packing materials and loading leeway.”

<voice from the crowd> “How come they had to be in space? It’d be a lot cheaper on the ground.”

“If you’re cynical you might say that NASA had built these shuttles and they needed to have some work for them to do. But the real reasons go back to Lyman Spitzer (name sound familiar?). Right after World War II he wrote a paper listing the benefits of doing Astronomy outside of our atmosphere. We think Earth’s atmosphere is transparent, but that’s only mostly true and only at certain wavelengths. Water vapor and other gases block out great swathes of the infrared range. Hydrogen and other atoms absorb in the ultraviolet and beyond. Even in the visible range we’ve got dust and clouds. And of course there’s atmospheric turbulence that makes stars twinkle and astronomers curse.”

“So he wanted to put telescopes above all that.”

“Absolutely. He leveraged his multiple high-visibility posts at Princeton, constantly promoting government support of high-altitude Astronomy. He was one of the Big Names behind getting NASA approved in the first place. He lived to see the Hubble Space Telescope go into service, but unfortunately he died just a couple of years before its IR companion was put into orbit.”

“So they named it after him?”

“They did, indeed. The Spitzer was the fourth and final product of NASA’s ‘Great Observatories’ program designed to investigate the Universe from beyond Earth’s atmosphere. The Hubble Space Telescope was first. It was built to observe visible light but it also gave NASA experience doing unexpected inflight satellite repairs. <scattered chuckles in the audience. The maybe-an-Art-major nudges a neighbor for a whispered explanation.> The Atlantis shuttle put Hubble into orbit in 1990. Thirty years later it’s still producing great science for us.”

<The maybe-an-Art-major yells out> “And beautiful pictures!”

“Yes, indeed. OK, a year later Atlantis put Compton Gamma Ray Observatory into orbit. Its sensors covered a huge range of the spectrum, about twenty octaves as Jim would put it, from hard X-rays on upward. In its nine years of life it found nearly 300 sources for those high-energy photons that we still don’t understand. It also detected some 2700 gamma ray bursts and that’s something else we don’t understand other than that they’re way outside our intergalactic neighborhood.”

“Only nine years?”

“Sad, right? Yeah, one of its gyroscopes gave out and NASA had to bring it down. Some people fussed, ‘It’ll come down on our heads and we’re all gonna die!‘ but the descent stayed under control. Most of the satellite burned up on re-entry and the rest splashed harmlessly into the Indian Ocean.”

<quiet snuffle>

“Cheer up, it gets better. A month and a half after Compton‘s end, the Columbia shuttle put Chandra X-Ray Observatory into orbit. Like Hubble, Chandra‘s still going strong and uncovering secrets for us. Chandra was first to record X-rays coming from the huge black hole at the Milky Way’s core. Chandra data from the Bullet Cluster helped confirm the existence of dark matter. Thanks to Chandra we understand Jupiter’s X-ray emissions well enough to steer the Juno spacecraft away from them. The good stuff just keeps coming.”

“Thanks, that helps me feel better.”

“Good, because it’s time for the Spitzer‘s inspirational life story.”

~~ Rich Olcott

A Far And Dusty Traveler

Cathleen takes the mic. “Quick coffee and scone break, folks, then Jim will continue our ‘IR, Spitzer And The Universe‘ symposium.” <pause> “OK, we’re back in business. Jim?”

“Thanks, Cathleen. Well, we’ve discussed finding astronomical molecules with infra-red. Now for a couple of other IR applications. First up — looking at things that are really far away. Everyone here knows that the Universe is expanding, right?”

<general murmur of assent, although the probably-an-Art-major looks startled>

“Great. Because of the expansion, light from a far-away object gets stretched out to longer wavelengths on its way to us. Say a sodium atom shot a brilliant yellow-gold 590-nanometer photon at us, but at the time the atom was 12.5 million lightyears away. By the time that wave reaches us it’s been broadened to 3540 nanometers, comfortably into the infra-red. Distant things are redder, sometimes too red to see with an optical telescope. The Spitzer Space Telescope‘s infra-red optics let us see those reddened photons. And then there’s dust.”

<voice from the crowd> “Dust?”

Cosmic dust, pretty much all the normal matter that’s not clumped into stars and planets. Some of it is leftovers from early times in the Universe, but much of it is stellar wind. Stars continuously spew particles in their normal day-to-day operation. There’s a lot more of that when one explodes as a nova or supernova. Dust particles come in all sizes but most are smaller than the ones in tobacco smoke.”

<same voice> “If they’re so small, why do we care about them?”

“Two reasons. First, there’s a lot of them. Maybe only a thousand particles per cubic kilometer of space, but there’s a huge number of cubic kilometers in space and they add up. More important is what the dust particles are made of and where we found them. Close inspection of the dust is like doing astronomical archaeology, giving us clues about how stars and galaxies evolved.”

<Vinnie, skeptical as always> “So what’s infra-red got to do with dust?”

“Depends on what kind of astronomy you’re interested in. Dust reflects and emits IR light. Frequency patterns in the light can tell us what that dust made of. On the other hand there’s the way that dust doesn’t interact with infra-red.”

<several voices> “Wait, what?”

The Milky Way from Black Rock Desert NV
By Steve Jurvetson via Flickr, Wikimedia Commons, CC BY 2.0

“If Al’s gotten his video system working … ah, he has and it does. Look at this gorgeous shot of the Milky Way Galaxy. See all the dark areas? That’s dust blocking the visible light. The scattered stars in those areas are simply nearer to us than the clouds. We’d like to study what’s back beyond the clouds, especially near the galaxy’s core. That’s a really interesting region but the clouds block its visible light. Here’s the neat part — the clouds don’t block its infra-red light.”

<other voices> “Huh?” “Why wouldn’t they?”

“It’s the size of the waves versus the size of the particles. Take an extreme case — what’s the wavelength of Earth’s ocean tides?”

<Silence, so I speak up.> “Two high tides a day, so the wavelength is half the Earth’s circumference or about 12’500 miles.”

“Right. Now say you’re at the beach and you’re out there wading and the water’s calm. Would you notice the tide?”

“No, rise or fall would be too gentle to affect me.”

“Now let’s add a swell whose peak-to-peak wavelength is about human-height scale.”

“Whoa, I’d be dragged back and forth as each wave passes.”

“Just for grins, let’s replace that swell with waves the same height but only a millimeter apart. Oh, and you’re wearing SCUBA equipment.”

“Have mercy! Well, I should be able to stand in place because I wouldn’t even feel the peaks and troughs as separate waves, just a foamy massage. Thanks for the breathing assistance, though.”

“You’re welcome, and thanks for helping with the thought experiment. Most cosmic dust particles are less than 100 nanometers across. Infra-red wavelengths run 100 to 1000 times longer than that. Infra-red light from those cloud-hidden stars just curves around particles that can stop visible lightwaves cold. Spitzer Space Telescope and its IR-sensitive kin provide deeper and further views than visible light allows.”

~~ Rich Olcott