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Kathryn Harkup, Chemist and Author of V Is for Venom, Joins Big Think to Discuss Why Christie Isn’t Just a Brilliant Writer But a Unique Science communicator.

— June 27, 2025

Cover Art For Sparkling Cyanide By Agatha Christie. Art by Leslie Leonard Stead (1899 - 1966) for the 1945 UK First Edition

Key Takeaways:

Agatha Christie’s background as a pharmacist’s assistant gave her a deep understanding of the poisons she skillfully weaved into her detective stories.

Harkup highlights how Christie subtly educates readers on the history and toxicology of various poisons without sacrificing narrative intrigue.

Christie’s use of poison not only advances plot and character but also reflects her meticulous attention to accuracy and good writing.

Dame Agatha Christie stacked up quite the body count during her long and esteemed career. The “Duchess of Death” wrote 66 detective novels, 14 short story collections, and 20 plays. Across those tales, her many victims were shot, bludgeoned, stabbed, electrocuted, strangled, run over, drowned, axed, and pushed off all manner of precipitous edges — from stairs to cliff sides — to let gravity sort out the messier details.

Christie has probably envisioned more creative ways to murder someone than Hannibal Lecter, Dexter Morgan, and Freddy Krueger combined, and readers have enjoyed solving her puzzle-box stories for a century — making her one of, if not the bestselling author of all time.

I’m one such reader. I’ve adored Christie’s stories since I picked up a well-worn Pocket Books edition of Murder on the Orient Express in a used bookstore my freshman year. The book is considerably older than I am yet retains a treasured perch on my bookshelf — that subtle fragrance of vanilla aged books acquire growing stronger with each reread. Value for money, it is easily the best $2 I’ve ever spent, and it kindled an enduring fondness for Christie’s characters.

But it wasn’t until I spoke with Kathryn Harkup, a chemist turned science writer, that I began to appreciate a side of Christie that I hadn’t noticed before.

“She’s a brilliant science communicator. She puts across all the science you need to know in her stories to be able to figure it out,” Harkup tells me during our conversation. “You (probably) won’t because she’s very good at disguising who’d done it. But all the science is there, and you never feel that you’re sitting through a chemistry lesson.”

Specifically, she is referring to when Christie plays the literary poisoner, a role that has delivered some of the author’s most beguiling and devious mysteries.

Harkup has dedicated two books to Christie’s poisons, the bestselling A Is for Arsenic (2017) and its sequel, V Is for Venom (2025). In each, she explores a dozen of the author’s chemical killers: their composition and toxicology, their history and traditional uses, how Christie employs them, and how their antidotes work (if they have one). She even dives into some disturbing real-life cases.

The books are part history, part scientific explainer, and part literary criticism that aren’t only fun, informative reads in their own right. They also heighten your admiration of Christie as a writer.

Christie’s goal was always to keep the readers guessing by delivering the deadly blow in an unexpected yet ultimately credible manner. When it came to her poisonous plots, she never drew attention to the science so as not to distract from the mystery. But in doing so, Harkup reveals, she leaves all the clues necessary for readers to begin learning about these noxious chemicals.

Death By Chocolate (But Mostly Poison)

When most people think of science communication in stories, their minds turn to science fiction. Makes sense — it’s right there in the name. This reputation is further cemented by the fact that many of the genre’s most respected writers either worked as scientists or held positions in scientific organizations. Think Isaac Asimov, Arthur C. Clarke, and Gregory Benford.

Like those authors, Christie brings a scientific background to bear in her stories, too. During the First World War, before becoming a writer, she worked as a pharmacist’s assistant at her local hospital. Before securing the job, she had to pass the exams and undergo strenuous training to handle the many chemicals stocked on the pharmacy’s shelves.

As Harkup points out, back in Christie’s day drugs didn’t come ready in pre-packaged pills. Pharmacists and their assistants were more like chemical cooks than dispensers. They measured, weighed, mixed, and packaged all manner of medical tinctures and creams in-house. They even added flavors and colorings to make bitter or unappealing concoctions palatable.

A Metal Plaque with a Portrait of Agatha Christie and text reading “Agatha Christie Mile, Torre Abbey” at Torre Abbey in her hometown of Torquay. Credit: Violetriga, Wikimedia Commons

Medicinal mishaps could prove deadly, and further complicating matters, prescriptions weren’t yet standardized. Doctors had their preferences for treatment and dosage, and pharmacists had to be careful. A mistake could deliver an unhealthy dose or combine drugs that react poorly together. In V Is for Venom, Harkup even shares a story where Christie saved a patient from a dangerous situation by noticing a mistake in the pharmacist’s calculations.

“Christie understood the difference between the therapeutic and lethal dose as well as appreciating the dangers of not doing her job properly,” Harkup writes. She also notes how the job introduced Christie to the many “quirks and little stories” surrounding these chemicals, showing her how people used them or how they might realistically find their way into someone’s home.

This experience and knowledge proved a boon to a future writer of detective stories.

Consider her short story “The Chocolate Box” (1923). Its victim, one Monsieur Paul Déroulard, dies from sudden heart failure. Those present note how his face flushed bright red before he collapsed to the floor. The cause was an overdose of nitroglycerin secreted into his favorite chocolates.

That may seem an odd, almost arbitrary choice. Nitroglycerin is famously the explosive ingredient in dynamite. Deadly, sure. But actually eating the stuff unawares? Hardly plausible, right?

It turns out that a small dose of nitroglycerin is also a reliable treatment for anginal chest pain because it dilates and relaxes blood vessels. A surplus, however, can drop a person’s blood pressure to fatal levels. Even so, it is generally considered safe and is still administered today in patches, sprays, and extended-release capsules. Early-20th-century pharmacology took a different route, though: chocolate.

The nitrate’s naturally sweet taste meant it paired well with cocoa. In fact, it is “the only medicine to have been officially prepared in chocolate tablets,” Harkup writes, and a book Christie likely studied for her exams, The Art of Dispensing, contains several recipes for nitroglycerin tablets. Thanks to this confectionary camouflage, the poor Déroulard never tasted the deadly additive.

In the story, this information — from the symptoms to the drug’s preparation to how they came to be in the house — is true to life. However, it isn’t presented as a lesson by some all-knowing character. It is revealed naturally as clues Poirot gathers by speaking with characters and making observations. The result feels far more engaging and dynamic than the vicarious lectures so many other stories, detective and science fiction, lean on.

Christie even one-ups her true-crime counterparts with this one. As Harkup points out, plenty of attempted assassinations have gone the death-by-poisoned-sweets route. In one famous case, someone tried to lace a walnut whip with strychnine (read: rat poison). The intended victim never ingested a lethal dose though. The reason: The foul taste led them to put down the chocolate.

“It was surprising where [Christie] found her inspiration,” Harkup says. “She was certainly a reader of true crime and fictional crime, but her pharmaceutical knowledge meant she could go to places where even criminals hadn’t thought of going.”

Murder Is Queasy

Another reason Christie’s poisons communicate their science so well isn’t just the nature of the tools. It’s also the nature of the crimes. As Harkup and I discuss, poison isn’t a heat-of-the-moment weapon. You don’t slip arsenic into someone’s tea because they cut in front of you at the bank.

“You really have to think about it,” she says. “You have to acquire the stuff. You have to figure out where you’re going to put it. Then you have to sort out your alibi and make sure the person doesn’t survive because some poisons are quite survivable.”

Such premeditation must be built into the story and revealed slowly through the detective’s investigation. This not only makes the clues satisfying to piece together but also allows Christie to make her poisons “characters themselves within the story” — complete with backgrounds and a kind of personality.

“The way the poisons will behave, you can sort of make predictions about it, and you can tell the characteristics of who might use them,” Harkup says.

A great example comes from the novel Murder Is Easy (1939). One of its many victims — the title is apt — is killed using oxalic acid. Oxalic acid isn’t uncommon for a poison. In fact, you probably have some in your home right now.

A low-grade corrosive, it’s found in cleaners and stain removers. It also occurs naturally in many foods. For instance, rhubarb stems are perfectly safe to eat if cooked, but the leaves should be tossed out because they store a potentially unsafe concentration of the stuff. Oxalic acid is so common that the trick isn’t acquiring the stuff; it’s finding a way to administer the poison that makes for a surprising yet satisfying mystery. And Christie doesn’t disappoint.

In Murder Is Easy, the killer swaps a bottle of cough syrup for hat paint, the latter of which contains a potent amount of oxalic acid. Back in the day, hat paint was used to change one’s on-the-town look without the expense of a new hat; however, it fell out of fashion decades before the story takes place. It’s also a poor choice of poison because it is easily treated. Had the killer not delayed medical aid by haphazardly jamming the door with a pair of pincers, the victim may well have survived.

Using the poison’s history and its characteristics, Christie subtly presents several important clues to who the killer is: their age, gender, social status, and even some elements of their personality. Slot those clues in with the others sprinkled throughout the story, and a sleuthy reader should know who the killer is well before the reveal.

A production crew films a scene of Poirot, a TV series based on Christie’s stories in which Sir David Suchet (center) plays her famous detective, Hercule Poirot. Credit: Wikimedia Commons

Pick Your Poison

I asked Harkup what her favorite Christie poison is, and she chose Christie’s use of hemlock in Five Little Pigs* (1942).

“It is brilliantly woven into the plot to the point where you need to read it twice to appreciate how good it is,” Harkup says. “When you go back, you’re like, ‘Oh God, yeah. I should have spotted that. That was damn obvious if I had paid attention to that particular bit.’ Her creativity is astonishing in that respect.”

She adds that Christie’s use of thallium poisoning in The Pale Horse (1961) is so accurate that the book is credited with saving two lives thanks to readers recognizing the symptoms from its description.

Of course, I had to know if Christie made any serious blunders or stretched the truth to the breaking point, and Harkup admits that Christie will sometimes push plausibility. For instance, she often has to concoct situations where medical aid is delayed, like in Murder Is Easy. Otherwise many of her stories would be shelved under attempted murder mysteries. She’ll also sometimes lower the deadly dose to something more manageable, like in “The Chocolate Box,” or speed up poisonings so readers don’t have to read about “hours of vomiting and diarrhea and convulsions” (which I definitely appreciate).

Even so, Harkup adds, Christie doesn’t fall back on the expedience of lazy poisoning clichés like many modern crime dramas — where someone takes one sip of wine, coughs twice, and falls down stone dead. Nor does she fabricate phony poisons like Arthur Conan Doyle did for Sherlock Holmes or Shakespeare in Hamlet.

Not that that’s a problem. “It only matters for a writer to be accurate within the world they have constructed. It’s an invented world, so they can do whatever they want as long as it obeys the rules of that world.” Even so, Harkup adds, “As a chemist, I appreciate it when people like Christie go to so much trouble to get things right.”

A Collection of Agatha Christie Novels. Credit: Kenny Louis / Wikimedia Commons

Death Comes As The End

As mentioned, Harkup also chronicles several true crimes featuring Christie’s poisons. “I was unfortunately blessed with an abundance of examples of the worst of humanity,” she says.

For instance, in 1901 a young woman was found dead with nitroglycerin residue in her stomach. Her suitor was brought to trial, where he was found to have provided the nitroglycerin under the false belief it was an abortifacient. However, the exact cause of death remains a mystery since the amount of nitroglycerin likely wasn’t enough to kill her. Alcohol, other substances, and perhaps even the morphine the doctors administered while treating her convulsions may have contributed.

Another incident Harkup recounts involves oxalic acid killing two people in 2015. The poison was found in Hokkaido tea, and given the amount, officials strongly suspected it was added deliberately. However, without concrete evidence or a strong motive pointing to a suspect, no one has been charged. The case remains unsolved.

“The Poisons Have Changed. The Manner In Which They’re Administered Has Changed, But It Still Happens,” Harkup Says.

What I found interesting about these true crimes wasn’t just the history but how they left me feeling. After reading them, a cold discomfort settled over my afternoon like a fog. That’s understandable given what these tales reveal about people, their inhibitions, and the random cruelty that can bring life to a sudden, unfair end.

But why do I find Christie’s stories so appealing then? Why, despite the murder, greed, and the worst of humanity on display, do these stories feel so warmly comfortable?

The poisons have changed. The manner in which they’re administered has changed, but it still happens.

Kathryn Harkup

I asked Harkup this question, and she answers that Christie’s fiction helps readers slake certain psychological thirsts that real life often fails to satisfy. The first is our desire for order and justice in a chaotic world.

“We want things to be fixed, sorted, and solved. I think there is a very basic need for us to have the bad guy punished and the good guys come out, if not victorious, then at least acknowledged in their rightness,” Harkup answers.

And what about the poisons themselves? As Harkup reminds me, many people are drawn to the risker side of science — the things that blow up, go boom, or move at supersonic speeds. Chemistry, she jokes, is a professional home for a bunch of “controlled pyromaniacs.” By making these dangerous chemicals the center of a fascinating puzzle, she combines that scientific desire for a solution and a safe amount of danger with a great story.

“It’s that extra layer of nastiness that fascinates us,” Harkup says. “[Stories are] a safe way of finding out about something that is so unknowable since the vast majority of us — I would hope — will never kill another human. It’s a safe trip into the darkest bits of the human psyche.”

We Understand Many Things About Our Universe, And Our Home Within it, Extremely Well. The Number of Stars In The Milky Way Isn’t Among Them.

— Ethan Siegel | Wednesday April 02, 2025

The Milky Way, as seen at La Silla observatory, is a stunning, awe-inspiring sight to anyone, and offers a spectacular view of a great many stars in our galaxy. There are approximately 6000 stars visible to the naked human eye, but the ones we can see are intrinsically brighter, bluer, and/or closer than the more typical, numerous stars of the Milky Way. We can only see the ones that are the easiest for our eyes to detect, and still don't know how many total stars are present within the Milky Way: due to large uncertainties at the low-mass end of the stellar spectrum. Credit: ESO/Håkon Dahle

It’s as simple and straightforward a question about our cosmic home as you can imagine: how many stars are in our Milky Way? While there’s an enormous amount that we know about our Universe with a significant amount of confidence — what types of matter and energy are present within it, how much of each species we have, how fast the Universe is expanding, how much time has elapsed since the hot Big Bang, how many galaxies are within it, etc. — learning some critical information about our own home within the cosmos has been exceedingly difficult. Although we live within the Milky Way, there’s a tremendous amount of information about it that we simply struggle to determine.

Our best picture of our galaxy, for example, requires an extensive amount of guesswork, as the galactic plane of the Milky Way is heavily dust-obscured, making it difficult to understand the structure of the far side of our galaxy. We know about our central bulge and bar, as well as our distance to the galactic center and its supermassive black hole, but we struggle with the shape, density, and thickness of our galaxy’s spiral arms and other properties of our galactic disk.

But perhaps the greatest, and simplest, fact that’s still unknown about the Milky Way is how many stars are present within it. While the most commonly cited figure is around 200 billion stars, some sources still cite a lower value of as little as 100 billion, while other sources prefer a higher value: perhaps as great as 400 billion. How can we know so little about our own galaxy, given our extensive knowledge of the Universe? There are major scientific reasons for our ignorance, and our uncertainty reflects the price we pay for being scientifically honest about what we have yet to figure out about our Universe.

The spiral galaxy UGC 12158, with its arms, bar, and spurs, as well as its low, quiet rate of star formation and hint of a central bulge, may be the single most analogous galaxy for our Milky Way yet discovered. It is neither gravitationally interacting nor merging with any nearby neighbor galaxies, and so the star-formation occurring inside is driven primarily by the density waves occurring within the spiral arms in the galactic disk.

Above, what you see is not the Milky Way, but rather a galaxy that shares many features in common with it: a modest central bar and bulge, two large, winding spiral arms with spurs coming off of them, a gas-rich disk, and a comparable diameter to our own of around 100,000 light-years. It’s not experiencing a major, distortive interaction with any other large neighbors, and its star-formation rate is low and quiescent: ongoing largely due to density waves occurring within its spiral arms. This galaxy, like many that are similar to it, may be an excellent candidate for the closest “twin” to our Milky Way of all the galaxies that are out there.

And yet, we don’t “know” for certain that this is at all reflective of the overall shape of the Milky Way and the large-scale features present within it. It’s sort of like being trapped in a world with no mirrors, cameras, or reflective surfaces, and being asked, “What do your own eyes look like?” It’s a mind-boggling question, because your eyes are the things you use to see: you look out from there. Although you’re able to see what everyone else’s eyes look like, and others can see your eyes, it’s impossible to see your own eyes without some sort of reflection, or some sort of externally acquired image, to inform you.

Behind the dome of a series of European Southern Observatory telescopes, the Milky Way towers in the southern skies, flanked by the Large and Small Magellanic Clouds, at right. Although there are several thousand stars and the plane of the Milky Way all visible to human eyes, there are only four galaxies beyond our own that the typical unaided human eye can detect. We did not know they were located outside of the Milky Way until the 1920s: after Einstein’s general relativity had already superseded Newtonian gravity. Credit: ESO/Z.Bardon/ProjectSoft

Fortunately, we can take all sorts of measurements that do provide us with a great wealth of information about the galaxy that we do inhabit. We can examine the plane of the Milky Way in a wide variety of wavelengths of light. Instead of being restricted to the optical part of the spectrum, where the gas, dust, and clouds of neutral matter within the galactic plane block and obscure the light sources (such as stars) that are located behind that material, we can look in a wide variety of different wavelengths of light, each one revealing a unique set of details about the Milky Way and what’s within it.

When we look at the shortest wavelengths, in the range of gamma-rays and X-rays, we see active black holes, neutron stars, and extremely hot plasmas, revealing everything from pulsars to flares at the galactic center.

When we look at optical wavelengths, we see stars in the foreground of this gas and dust, but only silhouettes of the objects behind them, as visible light is largely blocked by neutral matter.

And when we go to longer wavelengths than the human eye can see — at infrared, microwave, or even radio wavelengths — we can see the light-and-heat emitting sources, all the way down to temperatures that are only a few degrees above absolute zero, where these long-wavelength signals are transparent to the gas and dust that block visible light.

Most of our astronomical efforts, with telescopes, focus on a narrow region of the sky, as shown above for the Bok globule Barnard 68. The above animation shows the same region of sky — the same stars, the same gas, and the same dust features — viewed at a variety of wavelengths of light: from visible light at 440 nanometers (0.44 microns) all the way up to near-infrared wavelengths of 2160 nanometers (2.16 microns). For comparison, the visible light range spans from 400-700 nanometers and infrared wavelengths are longer-wavelength than that. As you can see, the gas and dust are extremely efficient at blocking optical (visible) light, but do worse and worse at blocking light the longer the wavelength we choose.

This is because the light-blocking material that the galaxy is filled with is largely composed of grains of dust of a finite size: a size comparable to the wavelength of light. In general, dust is very efficient at blocking light of wavelengths that are shorter than the size of the dust grains, and progressively less efficient at blocking light of longer wavelengths. (This is why dust-obscured regions appear redder, and dust-free regions appear bluer.) If we apply this technique — of looking at the whole sky, including the plane of the Milky Way, at longer, infrared wavelengths of light — we can do an outstanding job of “seeing through” the light-blocking gas and dust, and thereby reveal the stars that are located both within and behind those dust clouds, dust lanes, and any other shaped features that dust can produce.

By viewing the Milky Way in infrared wavelengths of light, we can see through large amounts of the galactic dust and view the distribution of stars and star-forming regions behind them. As revealed by the 2 micron all-sky survey (2MASS), the densest collections of galactic dust can be seen tracing out our spiral arms, but the center of the plane of the Milky Way is where the dust is densest. Infrared and visible light views both showcase this, but in vastly different ways. Credit: 2MASS/IPAC/Caltech & UMass

By peering through the plane of our Milky Way, including:

Into the galactic center and its surrounding regions,

Through the gas and dust and down, directly, the spiral arms within the galactic plane,

Away from the galactic center and toward the outskirts of the Milky Way,

And even clear through to the opposite side of the galaxy from the side the Sun is located within,

we can learn an enormous amount of information about the stellar extent of the Milky Way. This includes information about how large the stellar extent of the Milky Way is, whether it’s a straight disk or whether there’s a warp to it, what the stellar density is at all radii away from the galactic center, on average, as well as how the types and ages of stars present evolve as a function of distance from the galactic center.

By the mid-2010s, this led us to a profound conclusion about the total amount of mass that’s present in the form of stars within the Milky Way: about 60 billion solar masses worth of stars, with an uncertainty of around ~20% at that time. That’s an incredibly precise figure, as we had gathered enough information about the light in our Milky Way, even the light that gets blocked at optical wavelengths, to understand how much of it there was, and what the various numbers and types of stars were needed to produce them.

The (modern) Morgan–Keenan spectral classification system, with the temperature range of each star class shown above it, in kelvin. In terms of size, the smallest M-class stars are still about 12% the diameter of the Sun, but the largest main sequence stars can be dozens of times the Sun’s size, with evolved red supergiants (not shown) reaching hundreds or even 1000+ times the size of the Sun. A star’s (main sequence) lifetime, color, temperature, and luminosity are all primarily determined by a single property: mass. Credit: LucasVB/Wikimedia Commons; Annotations: E. Siegel

And yet, that small uncertainty in stellar mass still translates into a tremendously large uncertainty for the total number of stars present in the Milky Way: an uncertainty where pretty much all “guesstimates” between 100 billion and 400 billion stars were still viable.

How is this the case?

Because even a very precise, low-uncertainty figure for overall stellar mass (and stellar light) translates into a very large uncertainty for the population of the most common type of star: the faint, cool-temperature, low-mass, M-class red dwarf stars. There are the most common types of stars of all, and yet they emit far less light, even all combined, than the bigger, brighter, and rarer high-mass stars they’re born alongside.

Think about this non-intuitive fact: if you were to take a star like our Sun and either double or halve its mass, how much brighter or fainter would you expect that new star, of either 2 or 0.5 solar masses, to be? Do you think the twice-as-massive star will be twice as bright? Do you think the half-as-massive star will be only half as bright? Unsurprisingly, in order to know for sure, we have to get the relevant data directly.

Consider Sirius A: a star just 8.6 light-years away, with a mass that’s 2.063 solar masses. It’s a whopping 25 times as bright as our Sun.

Then consider Alpha Centauri B, just 4.3 light-years away also known as Toliman. It is indeed a star that’s half as luminous as our Sun, but it still has, impressively, 91% of the Sun’s mass.

If we look at a star like Lacaille 9352, 10.7 light-years away, which is half the Sun’s mass, you might be surprised to learn that it’s only ~4% as intrinsically bright as our Sun is.

This photo showcases Proxima Centauri: the closest star to our own Sun at present. Although it’s only 4.24 light-years away, Proxima Centauri is not even close to visible to the naked eye, as it’s intrinsically nearly 1000 times fainter than the Sun. Credit: Alessandro Cipolat Bares

So what happens, then, when we start thinking about the lowest-mass stars of all? What happens when we start considering stars like Proxima Centauri, shown above, which is actually the closest star to our Sun across the entire sky?

First off, despite being the closest star to the Sun, it’s not visible to the naked eye. In fact, it’s so faint that it wasn’t even discovered until 1915: just 110 years ago. At about 12% the mass of our Sun, it’s only about ⅐th the radius of the Sun, but much, much fainter than that. Intrinsically, Proxima Centauri is only 0.15% as luminous as the Sun, with nearly all of its energy being emitted in the infrared part of the spectrum. If we restricted ourselves to looking only in the visible light portion of the spectrum, we’d find that Proxima Centauri is only 0.005% as bright as the Sun, implying that it would take 20,000 stars similar to Proxima Centauri to appear as optically bright as the Sun.

This is where the greatest source of uncertainty lies: in the fact that we cannot measure the number of low-mass stars in the Universe, or in our galaxy, directly. Even the world’s most advanced, dedicated scientific collaboration to attempt to detect and find these low-mass stars, RECONS (the REsearch Consortium On Nearby Stars), has only been able to survey a tiny volume of space close to the Sun in its quest for the lowest-mass stars of all. Of the 270 star systems within 10 parsecs (33 light-years) of Earth that contain a “true star” within them, 82% of those systems are dominated by a red dwarf (M-class) star, with no brighter or more massive stellar member present at all.

This graphic compares a Sun-like star with a red dwarf, a typical brown dwarf, an ultra-cool brown dwarf, and a planet like Jupiter. Only about 5% of all stars are like the Sun or more massive; K-type stars represent 15% of all stars, while red dwarfs represent 75-80% (or more) of all stars. Brown dwarfs, although they are failed stars, may be just as common as red dwarfs are, but are cooler and lower in mass. Credit: MPIA/V. Joergens

In Other Words:

We can make a good estimate for the total amount of stellar mass, or mass in the form of stars, in the Milky Way, simply by measuring the total amount of starlight,

Which we can do directly from surveys, including all-sky surveys, including in infrared wavelengths of light,

And this tells us to a great degree of accuracy the number and abundance of Sun-like stars, more massive stars than the Sun, and cooler stars than the Sun down to about 40-50% of the Sun’s mass,

But that at the low-mass end of stars, including objects between 7.5-40% the mass of the Sun, tremendous uncertainties in the number and abundance of stars remain.

It’s the lowest-mass end of the stellar spectrum that houses the greatest uncertainty as far as their numbers go, because they contribute such a tiny, practically negligible amount of starlight (and mass) to the total stellar budget of the Milky Way.

However, all hope is not lost. One of the most powerful and compelling science missions of the last decade, in terms of how much it can teach us about our local Universe and our place within it, is the ESA’s Gaia mission. Located in space, Gaia observed the 3D positions and properties of nearly 2 billion stars within the Milky Way, determining their distance from us to better precision than any survey or catalogue before it. Gaia’s map of the stars within the Milky Way — the best one ever — has resulted in a number of new discoveries: the Milky Way’s warped disk, the full extent of its stellar disk, and superior distance determinations to a variety of features.

Gaia’s all-sky view of our Milky Way Galaxy and neighboring galaxies. The maps show the total brightness and color of stars (top), the total density of stars (middle), and the interstellar dust that fills the galaxy (bottom). Note how, on average, there are approximately ~10 million stars in each square degree, but that some regions, like the galactic plane or the galactic center, have stellar densities well above the overall average. Credit: ESA/Gaia/DPAC

One of the big advances that came along with Gaia, although it wasn’t necessarily well-publicized, was the best-ever estimate of the stellar mass of the entire Milky Way itself: about 50.4 billion solar masses worth of stars, with an uncertainty of approximately ~9-10% on that figure. This is consistent with, but a more precise and more refined version of, all previous estimates of the stellar mass of the Milky Way. This represents the best estimate of our galaxy’s stellar mass of all-time: the total amount of mass in the form of stars within the Milky Way. (Gaia also measures the Milky Way’s total mass, including dark matter.)

Interestingly, this produces a total amount of light that corresponds to about 150-180 billion Suns. How is this possible? Because the more massive, more luminous stars than the Sun dominate the light output of the stars within the Milky Way. In fact, there are several stars located within our Milky Way, including:

The Pistol Star,

Wolf-Rayet star WR 89,

The central bright star in Eta Carinae,

And star Westerhout 49-2,

are all only a few dozen to perhaps a couple of hundred times as massive as the Sun, but are millions of times as luminous as the Sun is. The more massive, bluer stars in the Milky Way dominate its light output, despite being so few in number, while the more numerous, redder, but less massive stars dominate the total “number of stars” within the Milky Way, but produce very little of the Milky Way’s total light.

Way’s stellar mass, over time, with the latest (2020) data informed by the ESA’s Gaia mission. With a stellar mass of ~50 billion Suns, but hundreds of billions of stars inside the Milky Way, it’s the red dwarf stars that create the largest uncertainties in the total number of stars within our galaxy. Credit: E. Wang & S.J. Lilly, Astrophysical Journal Accepted/arXiv:2308.02366, 2023

And that’s where we are today. We understand very well the total amount of light produced by the stars within the Milky Way: produced largely by the small percentage of stars that are greater in mass than the Sun, and augmented by Sun-like and slightly less massive stars. This understanding enables us — particularly with data acquired from the ESA’s Gaia mission about the stars in the Milky Way, directly — to draw compelling conclusions about the total amount of stellar mass, or mass in the form of stars, present in the Milky Way. Our best estimate for that is ~50 billion solar masses worth of stars, with an uncertainty of just ~10%.

However, our lack of understanding about the lowest-mass end of the stellar spectrum, and how many red dwarf stars there are of between 7.5-40% the mass of the Sun, results in tremendous uncertainties down there. With the latest data, the total number of stars in the Milky Way could reasonably be as low as ~200 billion, but not as low as the ~100 billion estimate that so many astronomers used in the late 20th century. However, it still could be as high as ~400 billion; the data remains consistent with that larger number as well.

Americans Have Gone Through Three Historic Junctures Like What We’re Witnessing Today — And They Happen On An Uncanny 80-Year Cycle.

— Wednesday April 02, 2026 | Peter Leyden

The last time America went through anything comparable to what we are going through today, it was coming off the Great Depression and World War II and about to head into the post-war economic boom, as represented in the graphic above.

America in the year 1945 and America in 2025 have many parallels that are worth contemplating today. Like today, that America faced a rare epic juncture in the nation’s history and even in world history. The technological and economic forces driving through the era were just as transformative as today’s, and the political stakes around the outcome were just as high. The systems that were about to scale up in the next 25 years for them were dramatically different from the systems that came before — just like the systems that are about to scale up for us.

America has been through this drill before, like exactly 80 years before, but what’s even more remarkable is that we have been through this kind of fundamental reinvention two other times in the history of the country — once around the Revolutionary War in the late 18th century and then again around the Civil War in the middle of the 19th century. The most uncanny thing about this cycle of reinvention is that each one happens almost exactly 80 years after the last.

The More You Understand This Pattern of The Past, The More You Will Understand What’s Really Going On Today

This essay is going to lay out the remarkable parallels between today’s America and the nation during each of its previous periods of fundamental reinvention. It will compare our pivot year of 2025 to the previous pivot year of 1945 and the end of World-War II, and then to the end of the American Civil War in 1865, exactly 80 years prior. It will then go back another 80 years to 1785, just after the Revolutionary War as the founders were gearing up for the Constitutional Convention.

In each of these periods, Americans found themselves at a juncture. The old systems that had long served them well had been breaking down over the previous 25 years and needed to be superseded. At the same time, they were facing a period of explosive growth — driven by new technologies that required widespread innovation throughout the economy and society — that would last for the next 25 years. The graphic above captures that juncture between the old world dying and the new world struggling to be born in 1945.

At each of these junctures, smack in the middle of the dying world and the new world struggling to be born, political passions run extremely high, and the country polarizes around two political options for its future. The more you understand this pattern of the past, the more you will understand what’s really going on today.

My new series, The Great Progression: 2025 to 2050, will go beyond explaining today, and explain what the next 25 years of our coming long boom could bring. The graphic above from the initial overview essay shows what’s happening now and can act as a reference point when looking at the comparable graphics for our past historical eras.

Much of the material to come in this series will be future-focused. I’ll detail our opportunity to harness the world-historic general-purpose technology of artificial intelligence to transform our economy and society in myriad ways. I’ll also explain how other transformative technologies, such as clean energies and bioengineering, could be used to bring fundamental system changes and help solve the most daunting challenges that we now face.

But to help convince you to take these future projections seriously, I’m going to walk you through the three other times America has faced a comparable historic juncture and met the moment with a fundamental reinvention that lasted roughly 25 years and created models that helped point the new way forward for the rest of the world.

The Post-World War II Boom and The Remaking of The International Order

If you have any living relatives from the GI Generation, ask them to explain what they know about the last great period of American reinvention, which is captured in the graphic at the top of this piece. (My 95-year-old mother is among the last of that generation, and I am doing just that.) This is not ancient history — this is within living memory of some Americans still with us today.

The GI Generation has been called the Greatest Generation, and that’s because its members, including John F. Kennedy (JFK), not only fought against fascism as young people in World War II, but also, just as importantly, helped build out the new America and new world order in the great boom that followed, with JFK becoming the first of seven US presidents from the generation. They were the players during this crucial juncture. What did they experience?

By the time World War II ended in 1945, the GI Generation and all Americans of that era had already lived through several major developments that have parallels today. They had watched the rapid deterioration and dysfunction of the old economic systems that worked relatively well for previous eras — until they didn’t. At the end of the Roaring Twenties, they saw the great stock market crash of 1929 and the beginning of the Great Depression, a period of widespread unemployment and hardship for the vast majority of working people not just in America but throughout the developed world.

By 1945, Americans had lived through a period of ferocious domestic politics with two sides in a titanic struggle that often flirted with violence but stopped short of outright civil war. The more conservative side was marked by the rise of the America First movement and an American version of fascism that increasingly took over the Republican Party through the 1930s. The other, more progressive side was marked by the emergence of President Franklin Delano Roosevelt (FDR) and a new kind of Democratic Party that tried out early experiments in what scaled up into the modern welfare state after WWII. (See the graphic at the top of this section.)

In the pre-war period, Americans watched the rise of the new powers of Japan and a resurgent Germany and endured a period of such ferocious geopolitical struggle that it led to an all-out world war. By 1945, the entire international order needed a wholesale reinvention — and that’s exactly what happened. In just a handful of years, the world saw the creation of the United Nations, the World Bank, the International Monetary Fund, NATO, and many other completely new international institutions.

The level of reinvention on the domestic front after the war was just as extraordinary. Americans of that era seized on the new technologies that had emerged before and during the war and dramatically scaled them up. Nuclear fission was only discovered in 1938, but after the war, the nuclear power industry exploded in growth alongside our nuclear bomb arsenals. Many of the technologies developed before the war and refined during it — such as mainframe computers, commercial aviation, and plastics — were poised to take off after its conclusion.

“The Point of Revisiting This 20th Century History Is To Help You See All The Parallels To Our American Moment.”

The post-war boom brought an incredible build-out of new public infrastructure in the form of the interstate highway system, suburbs outside of all central cities, and a huge expansion of schools and institutions of higher education to accommodate the Baby Boom.

The economy was deliberately and fundamentally restructured to avoid the mistakes of the old system, which had led to huge wealth inequalities and the financial crash and depression. The rich were taxed 90% on income in the highest tax bracket — that rate had never been contemplated before, but it stayed in place for 20 years. America built its version of a welfare state that protected average workers and citizens, and it led to a big push for the Great Society programs and the expansion of civil rights in the 1960s.

All of this happened in the space of just 25 years after the war, from 1945 to 1970. During this period, similar changes occurred throughout Europe and the West, but by the 1970s, the entire post-World War II boom, what many have called the Golden Age of Capitalism, had started to slow with oil shocks and stagflation.

The point of revisiting this 20th century history is to help you see all the parallels to our American moment. We have our own old 20th century systems that are breaking down and causing more problems than they solve. If you’re on the right, you will rail about the old bureaucratic systems of government. Fair enough. If you’re on the left, you will rail against old carbon energy systems that are causing catastrophic climate change. True too.

We also have our versions of transformative general-purpose technologies. Clean energy in the form of solar cells and electric vehicles are poised to replace carbon energies and the internal combustion engine. We have bioengineering tech that could create materials to supersede plastics. Artificial intelligence, the most transformative technology of all, is ready to reinvent pretty much everything.

We have our version of a ferocious domestic political struggle that is far from settled, too. President Donald Trump and his MAGA Administration have won the most recent battle, but that isn’t the same as winning the war. He is accelerating the dismantling of the old domestic bureaucratic state and the Pax Americana, but he seems to have no real plan for what to build in its place. The story of the next 25 years is just beginning.

But that will take another essay. Let’s go deeper into American history for now.

The 80-Year American Reinvention That Actually Went Into Civil War

Go back another 80 years from 1945, and you arrive at 1865 and the end of the Civil War, the most ferocious political battle Americans have ever gone through. By the time we finally settled that one, 750,000 Americans were dead.

This juncture is the best one to drive home the point about why political passions run so high at these historic moments: They mark fundamental system changes, and the stakes are extremely high, particularly for those on the side of the system that has to die.

In the 1850s, America started facing up to the fact that its economy was built on two fundamentally incompatible systems: one based on free labor essential to a growing manufacturing economy in the North, and one based on slave labor essential to the agricultural economy of the South. These two systems had been in tension from the founding of the country, but the contradictions had become unsustainable by the middle of the 19th century.

Freeing the slaves was framed as a human rights issue, but it also was an economic issue that was central to how the political and economic system of the Southern states worked. The political leaders and economic powers of those conservative Southern states were so threatened by the looming system change of dismantling slavery that they banded together in the Confederacy and declared a war of secession.

The war took four years to resolve the slavery issue once and for all, but once settled, America went into an explosion of reinvention that rolled out for the next 25 years. The most dramatic difference came to the South with what we call the Reconstruction, which is another way of saying the Reinvention.

“Each of These American Reinventions Is Partly Driven By New Technologies That Have Reached The Point Where They Can Start To Scale.”

The Reconstruction started out as an idealistic plan to reinvent the Southern states, primarily through integrating freed slaves into the free market economy and giving them the vote. We added the 13th, 14th, and 15th Amendments to the Constitution and kept troops stationed throughout the South to enforce myriad changes. We now look back on the Reconstruction more as a failure than a success because white powerbrokers unwound many of the reforms and undermined the voting rights of former slaves for all practical purposes when these troops were pulled out in 1877.

America as a whole after the war went through an unambiguous period of great progress from 1865 to 1890. Although President Abraham Lincoln was assassinated just days after the end of the war, during his time in office, he and the progressive Republican Party that dominated Congress passed laws that helped transform the country in the coming decades.

The Homestead Act, which gave 160 acres of free land to settlers, drove westward expansion and became a cornerstone of that era’s version of the American Dream. The Morrill Land-Grant Colleges Act dramatically expanded access to higher education for average Americans and spurred scientific advancement in many industries. Lincoln also signed the law that funded the Transcontinental Railway that eventually reached all the way to San Francisco.

The mention of trains brings up the technological side of all these historic junctures. Each of these American reinventions is partly driven by new technologies that have reached the point where they can start to scale and so more fundamentally transform the country. The discovery and early development of the new tech comes in the 25 years prior to the inflection point, but its major impact comes in the 25 years after we cross it.

America had seen trains before the Civil War, but they were small scale and centered around cities — the entire country had less than 30,000 miles of iron track. By 1890, though, the nation had about 170,000 miles of track connecting the entire continent. Thanks to the revolutionary Bessemer steel process, these tracks could be made of steel, too, which was more durable, safer, and capable of supporting heavier loads. With an ability to move freight and luxury passenger cars anywhere, America was a different nation.

“Four score and seven years ago our fathers brought forth on this continent, a new nation, conceived in Liberty, and dedicated to the proposition that all men are created equal.” That’s the opening line of Lincoln’s Gettysburg Address, which some of you can probably recite by heart.

A “score” meant 20 years, or the span of a generation, in the formal language of Lincoln’s time, so “four score and seven years ago” was his way of saying “87 years ago.” Travel 87 years back from 1863, the year Lincoln gave his speech, and you arrive at 1776, the year the Declaration of Independence was signed.

With the Gettysburg Address, Lincoln was saying that America was founded 87 years ago, and now, Americans of his era were being called upon to refound the nation on the principle that all men are created equal — for real this time. He was calling for a reinvention of America two years before the war was won.

So now let’s go back another “four score” years in American history, from the end of the Civil War in 1865 to 1785, when our founders were gearing up to invent America for the very first time at the Constitutional Convention.

The Original American Founding and Key Role In The Enlightenment

Now the story gets a bit more complicated because we need to step further back to take in an even bigger picture.

The United States in 1785 was a dinky nation of barely 4 million people scattered across 13 former British colonies stretching along the long coast of the Atlantic. The best way to understand the America of that time is to think of it as part of a much bigger Western Europe that was going through civilization-scale change in what we now call The Enlightenment.

The Enlightenment lasted from roughly 1680 to 1800, and during it, this expanded version of Western Europe created nothing short of a new civilization based on the invention of at least six new foundational systems that we are still working within today.

I’ll later do a whole essay on this, but for now, think of those core inventions as mechanical engines, carbon energies (starting with mined coal at scale), industrial production, financial capitalism, nation states, and, finally, representative democracy.

In other words, The Enlightenment invented six things with the potential to fundamentally change the world (and that did change the world with time). A couple of them had to do with foundational technologies, a couple laid the foundation for a different kind of economy, and a couple, introduced at the end of the period, laid the groundwork for a new kind of politics and government.

To give credit where credit is due, the nations of Western Europe, particularly Great Britain, invented the first five of these. But the former colonies of the United States can take credit for inventing representative democracy. (France gave it a shot around the same time but ended up devolving into a dictatorship.)

“A Very Different World Is Now Within Reach.”

The point is that what America invented from 1785 to 1810 was a civilization-scale innovation with ramifications for the entire world. The founding fathers wiped clean the proverbial whiteboard and started sketching out how a nation of free and equal people could create a true democracy — one that captured the will of the majority of people, but also protected the rights of the minority in a pluralistic society and that was built to withstand the return of tyranny. They came up with a plan that they concretized in a constitution, established a way to amend it over time, and then started the grand experiment.

The point of this essay is that America might be at another historic juncture of that magnitude. We in 2025 might be at the point of having to face up to what it would take to fundamentally invent a new kind of civilization.

Why? The shortest answer is the arrival of artificial intelligence, which signals the beginning of an age of intelligent machines. This world-historic development will increasingly allow humans to actually do a wide range of things that humans in all previous eras would only understand as magic.

Beyond AI, there’s a wave of other potentially world-changing 21st-century technologies, including tools that give us the ability to bioengineer all living things. Soon, we may be able to create abundant clean energy with the fusion process powering the stars. A very different world is now within reach.

America may be entering a time of such fundamental invention that we need to go back to the spirit of the founders, clean the proverbial whiteboard, and start sketching out how to invent new economic, societal, and governmental systems that take full advantage of 21st-century technologies and our new knowledge of how the world actually works — and how it can now be made much better.