Science Can’t Explain Everything

Hello, friends!

As you know, I love science.  I’m a little obsessed.  But there are people who get annoyed or even offended by my obsession with science, and every once in a while one of these people will remind me, sternly, that science can’t explain everything.  And you know what?  I generally agree with that sentiment.  But then people start declaring that science will never know this specific thing or that specific thing, and I immediately think of a certain 19th Century French philosopher named Auguste Comte.

Comte was not some scientifically illiterate buffoon.  He wasn’t one of those 19th Century evolution deniers, or one of those latter-day opponents to the heliocentric model of the Solar System.  In fact, Comte is regarded today as the very first philosopher of science, in the modern sense of that term, and he gets credit for coining the word “sociology” and for laying the philosophical foundation for that entire branch of science.  There’s also a wonderful quote from Comte about the mutual dependence of scientific theory and scientific observation.  Basically, you can’t formulate a theory without observation, but you also can’t make an observation without the guidance of a theory.

But that is not the Comte quote I think of whenever somebody starts lecturing me about the things science will never know.  It’s this quote about the stars: “[…] we shall never be able by any means to study their chemical composition or their mineralogical structure…”  Comte also declared that: “I regard any notion concerning the true mean temperature of the various stars as forever denied to us.”

Comte wrote this in 1835, and if you can put yourself into an 1835 mindset you can see where he was coming from.  There’s no such thing as rocketry.  We don’t even have airplanes yet.  And even if you could fly up to a star (or the Sun), how would you measure its temperature?  What kind of thermometer would you use?  And how would you go about collecting stellar material, in order to determine the star’s chemical composition?

According to Comte—a highly intelligent and very pro-science person—this sort of knowledge was utterly impossible to obtain.  And yet only a few decades later, thanks to the invention of the spectroscope, scientists started obtaining some of this unobtainable knowledge.  For those of you who don’t know, spectroscopes separate light into a spectrum.  Some parts of the spectrum may appear brighter or darker than you might otherwise expect, depending on which chemical substances emitted or absorbed the light before it reached the spectroscope.  And so by comparing the spectral lines of chemicals we have here on Earth to the spectrum obtained from the light of a star, you can determine the chemical composition of that star.

You can also measure a star’s temperature thanks to a concept known as black body radiation.  Basically, black body radiation refers to the fact that things glow as they got hotter.  If no other light sources are involved, then the color of a glowing object will be directly related to that object’s temperature.  Ergo, if you know what color a star is, then you can work out a pretty accurate estimate of what temperature that star must be.

Auguste Comte didn’t foresee any of this.  It is certainly true that science does not know everything, and there are surely things that science will never know.  But if you think you know, specifically, what science can never know, I question that.  Someday, some new invention (like the spectroscope) or some breakthrough discovery (like black body radiation) may turn an utterly unknowable thing into a matter of trivial measurements and calculations.

Maybe the one thing science truly can never know is what science’s own limitations are.


Here’s a very brief post about Auguste Comte, what he said about stars, and how epically wrong he was with that one prediction.

Also, here’s a short article about some genuine limitations that science has, like aesthetics, moral judgements, etc.

Sciency Words: P-P Chain

Hello, friends!  Welcome to Sciency Words, a special series here on Planet Pailly where we discuss the definitions and etymologies of scientific terminology.  In today’s post, we’ll be discussing the scientific term:


I have, in the past, been accused of covering scientific terms on the basis of how silly they sound, rather than on the basis of pure scientific merit.  But I would never do such a thing.  I have far too much respect for both science and linguistics.  Now with that unambiguously established, let’s talk about the p-p chain.

Definition of the p-p chain: In the field of nuclear physics, the p-p chain refers to a series of nuclear fusion reactions, starting with the fusion of two protons and leading, ultimately, to the creation of a helium-4 nucleus.  The p-p chain is by far the most common fusion process occurring in the core of the Sun, as well as other stars of similar or smaller sizes.

Etymology of the p-p chain: The p’s in p-p chain refer to the two individual protons that fuse together in the very first step of the process.  English astronomer Sir Arthur Eddington first proposed that proton-proton fusion might be occurring inside stars, writing about it in a 1926 article titled “The Internal Constitution of the Stars.”  German-American theoretical physicist Hans Bethe worked out the step by step details of the process in a 1939 paper called “Energy Production in Stars.”  Sadly, I cannot give credit to either Eddington or Bethe for coining this term.  They came up with the idea and worked out the details, but I have not been able to determine who, exactly, first introduced the term “p-p chain” into the scientific literature.

There are at least three versions of the p-p chain, each with different intermediate steps between the individual protons at the start and the helium-4 nuclei at the end (a fourth version is possible in theory, but has yet to be verified in reality).

Recently, scientists at the National Ignition Facility (NIF) in California made significant progress in nuclear fusion research.  That recent experiment has been described as recreating the power of the Sun here on Earth, which is true enough.  But NIF did not recreate the entire p-p chain from start to finish; they did something loosely equivalent to the very last step only.  It seems that reproducing the whole chain is still beyond our current scientific abilities.

So the next time you notice the Sun, shining yellow-gold in the sky, just remember that she can still do p-p chains in ways we humans cannot.


If you’re looking for a more detailed and technical explanation of the p-p chain (and the three or four variations thereof), check out this article from  That article was my main source of information while writing this post.

You can also find Arthur Eddington’s “The Internal Constitution of the Stars” by clicking here and Hans Bethe’s “Energy Production in Stars” by clicking here.

And if you’re looking for a fun way to try nuclear fusion for yourself, check out the game Fe[26].  You slide around tiles marked with the names of different atomic nuclei, trying to combine them to make bigger and bigger elements.  Which nuclear combinations work and which ones don’t?  Play and find out for yourself!

Sciency Words: Barycenter

Hello, friends!  Welcome to Sciency Words, a special series here on Planet Pailly where we talk about those super weird (but super cool) words scientists like to use.  Today’s Sciency Word is:


Tell me if you’ve heard this one: every action has an equal and opposite reaction.  This is true even for moons orbiting planets, or planets orbiting stars.  Whenever a star exerts gravitational force on a planet, that planet exerts an equal and opposite gravitational force on the star.  As a result of this ongoing gravitational tug-of-war, we end up with a planet and a star spinning round and round their common center of mass, a point which scientists call a barycenter.

Definition of barycenter: In astronomy, a barycenter is the center of mass of two or more objects in space that are gravitationally bound together.  

Etymology of barycenter: The word barycenter traces back to a Greek word meaning “weighty” or “heavy.”  The word barometer has a related etymology (barometers measure atmospheric pressure—the “weight” of the atmosphere, in other words).

Sometimes a barycenter will be located deep inside the more massive of two celestial bodies, in which case the more massive body will appear to wobble in place.  This is the case for the Earth and the Moon.  The Earth-Moon barycenter is approximately 1700 km beneath Earth’s surface.  Other times, the barycenter will be somewhere in the empty space between objects.  For an example, look at Pluto and its largest moon, Charon.  The Pluto-Charon barycenter is more than 900 km above the surface of Pluto.

The concept of a barycenter dates back to Isaac Newton (though I can’t find any sources saying he coined the word, nor could I find any evidence that he ever used the word himself).  Newton’s Principia Mathematica, originally published in 1687, briefly discusses the Sun-Jupiter barycenter, saying, “[…] the common centre of gravity of Jupiter and the sun will fall upon a point a little without the surface of the sun.”  Newton also discusses the Sun-Saturn barycenter, which he describes as “[…] a point a little within the surface of the sun.”

And then there’s the barycenter of the Solar System as a whole: the “common centre of gravity of all the planets,” as Newton calls it.  Due to the combined gravitational forces of all the planets (most especially that of the giant planets: Jupiter, Saturn, Uranus, and Neptune), the Sun is constantly being pulled in multiple directions at once.

As a result, the Sun does not sit still in the middle of our Solar System.  It is “agitated by perpetual motion,” to quote Newton one last time.  Sometimes, as the Sun moves about, it happens to pass through the Solar System’s barycenter. Other times, it loops and spirals around the barycenter, as if performing an elaborate dance.


Here are a few articles that go into a little more detail about barycenters:

And here’s a link to the translation of Newton’s Principia Mathematica that I quoted in this post.  The relevant section is titled “Proposition XII.  Theorem XII.”

Now Open: The Planet Pailly Store!!!

Hello, friends!

If you’ve ever looked at my artwork and thought it would look good on a T-shirt or a notebook cover or a tote bag, well… I have good news for you!  The Planet Pailly store is now open on!!!

You can get my artwork printed on shirts or coffee mugs or throw blankets… there’s a shockingly wide selection of stuff you can buy.  You can also get stickers in various sizes, so feel free to slap my artwork on anything and everything you want!

Now I was initially concerned about quality.  Redbubble is a print-on-demand service, and I’ve had some bad experiences with print-on-demand services in the past.  But I can assure you that Redbubble stuff is top quality.  I am really, really happy with the way this T-shirt turned out.

This spiral notebook is also really cool.

My only complaint is that Redbubble doesn’t offer free shipping.  They do, however, offer bundle discounts if you order multiple items at once.  So if you buy a T-shirt from me, and maybe a shower curtain from another artist, and a set of coasters from somebody else, your discounts should start stacking up nicely.

The Planet Pailly store currently has three “highly technical diagrams” that have previously appeared on this blog: the Sun, Jupiter, and Pluto.  More astronomical objects will be added soon (if you have requests, let me know in the comments).  Also coming soon: the cover art from Tomorrow News Network.

So if you’re looking for the perfect gift for your sciency friend, or the perfect gift for your sciency self, please check out my Redbubble store.  And be sure to check out some of the other artist stores on Redbubble too!  There’s cool stuff for everybody, and your money will help independent artists (like me) keep doing what we do.

Sciency Words: Syzygy

Hello, friends!  Welcome to Sciency Words, a special series here on Planet Pailly where we take a closer look at the definitions and etymologies of scientific terms.  Today on Sciency Words, we’re talking about the word:


We’ve all seen pictures like this, with all eight planets lined up in a row:

And sometimes, on extra special occasions, the planets really do line up like that, or at least they come very close to it.  When this happens, we call it a grand syzygy.

The word syzygy traces back to ancient Greek.  It originally meant “yoked together,” as in: “The farmer yoked together his oxen before plowing the field.”  According to my trusty dictionary of classical Greek, the word could also mean “pair” or “union.”

Some closely related words in Greek referred to balance, teamwork, sexy times, etc.  And our modern English words synergy and synchronized have similar etymologies.  Basically, what all these words have in common is a sense of people or things coming together, in one manner or another.

For modern astronomers, syzygy means three or more celestial bodies coming together to form a straight line.  The most commonly cited example of this is the alignment of the Sun, Earth, and Moon that occurs during either a new moon or full moon, as observed here on Earth.

But an alignment doesn’t have to be perfectly straight to be called a syzygy, especially when we’re dealing with more than three objects.  According to this article from The New York Times, a syzygy of the Sun, Venus, Earth, Mars, Jupiter, and Saturn occured between March 25 and April 7, 1981.  The Sun and five planets came “within 2 degree of arc from a perfect straight line.”  Apparently that’s close enough.

But while that 1981 syzygy was pretty grand, it was not the grandest of grand syzygies.  The planets Mercury, Uranus, and Neptune were left out.  According to another article from The News York Times, a truly grand syzygy will happen on May 19, 2161, “[…] when eight planets (excluding Pluto) will be found within 69 degrees of each other […].”

So mark your calendars, friends!  You don’t want to miss the grand syzygy of 2161!

P.S.: And if you’re a Star Trek fan, you may recall that 2161 will be an auspicious year for another reason.  That’s the year when the United Federation of Planets will be founded—a political syzygy, one might say, occurring at the same time as an astronomical syzygy.

A Rainy Day on the Sun

Hello, friends!

I was recently introduced to a new song by Jean Grae entitled “Stop Drawing Sunglasses on the Sun” (click here).  The song raises some valid points.  As an artist who frequently draws sunglasses on the Sun, I guess I have some soul-searching to do.

In the meantime, I recently saw a report on that said it was raining on the Sun.  So naturally, I drew this:

Pretty much everything associated with the Sun it extremely big, extremely hot, and relates somehow to the Sun’s extremely powerful magnetic field.  The Sun’s coronal rain (no relation to the coronavirus) is no exception.

First, let’s talk about the role of the magnetic field.  Ionized gas (a.k.a. plasma) rides up the Sun’s magnetic field lines to form solar prominences: those arch-like or loop-like structures that are often seen suspended above the Sun’s surface.

These prominences are extremely hot, at least by Earth standards, but they’re not quite as hot as the Sun’s surface.  According to this paper from Astrophysical Journal Letters, there are at least two possible explanations for how solar prominences loose their heat.  Whatever the cause of the heat loss, the result is that the cooling plasma begins to condense, much as cooling water vapor condenses in Earth’s atmosphere.  And then rain drops start to form.

But of course, these rain drops are extremely big, more like “rain blobs.”  Due to the technical limitations of Earth-based and space-based solar observatories, we can’t say for sure how big these rain blobs get, but some appear to be “on the order of 5000 km in radius,” according to that same paper from Astrophysical Journal Letters.

So in summation, it rains on the Sun.  Seriously, it rains a lot!  And like pretty much everything else relating to the Sun, this coronal rain is extremely big, extremely hot (by Earth standards), and is associated with the Sun’s extremely powerful magnetic field.  So maybe the Sun doesn’t need sunglasses, but an umbrella seems appropriate.

Next time on Planet Pailly, what is so super about a supermoon?

Sciency Words: Solar Wind

Hello, friends, and welcome to another episode of Sciency Words.  Each week, we take a closer look at some science or science-related term so we can expand our scientific vocabularies together!  Today on Sciency Words, we’re talking about:


The stars twinkle in our sky because Earth’s atmosphere scatters starlight.  The Sun has an atmosphere too, so it shouldn’t surprise you to learn that when astronomers observe stars that happen to be near the Sun (as viewed from Earth), they can see that the Sun’s atmosphere also scatters starlight.

What might surprise you—and what did surprise astronomers in the 1950’s—is that this scattering effect can extend very, very far into the space around the Sun.  The Sun’s atmosphere must be huge!  As reported in this 1959 article from Scientific American, the Sun’s atmosphere might be so big that it encompasses Earth!

Pursuing this and other lines of evidence (such as the apparent correlation between flare activity on the Sun and aurorae here on Earth, as well as apparent 11 year fluctuations in cosmic radiation levels), American astrophysicist Eugene Parker wrote this paper in 1958, introducing a concept now known as the solar wind.

As you might imagine, the Sun’s atmosphere is hot.  Absurdly hot.  Remember that temperature is really just a measure of the average velocity of atoms, and you’ll soon realize (as Parker did) that atoms in the Sun’s atmosphere must have enough velocity to escape the Sun’s gravity.  And since those atoms would also be ionized, these streams of ionized particles coming from the Sun would serve as extensions of the Sun’s magnetic field.

The term solar wind doesn’t appear in that 1958 paper.  Parker first introduces that term in this 1959 paper, in which he defends his idea and responds to critiques from other astrophysicists.  As Parker explains:

In view of the simple hydrodynamic origin of the expansion, it seems appropriate to term the stream a solar wind.

Also in 1959, the Soviet Union’s Luna 1 space probe gathered the first empirical evidence that the solar wind really does exist, leading to confirmation that Eugene Parker’s solar wind hypothesis was correct.

And today, a NASA spacecraft named in Parker’s honor is spiraling closer and closer to the Sun, gathering more data about the solar wind and other mysterious phenomena associated with the Sun.

Next time on Planet Pailly, now that we’ve talked about the solar wind in our own Solar System, we’ll check out the space weather forecast for the solar system next door.

Sciency Words: Barycenter

Hello, friends!  Welcome to Sciency Words, a special series here on Planet Pailly where we talk about those big, complicated words scientists use.  Today’s Sciency Word is:


Excuse me, but I’m going to do that “um, actually” thing that people who think they’re really smart like to do.  Now you may think the Earth orbits around the Sun.  Um, actually… the Earth and Sun both orbit something called the barycenter.

The word barycenter comes from two Greek words meaning “heavy” and “center,” and it refers to the common center of mass for two or more celestial bodies.  Based on sources I found via Google Ngrams, the term started appearing frequently in astronomical journals during the early 20th Century, and it may have been in use as early as the 1880’s.

Let’s say you have two celestial bodies.  One is really massive, the other is much less massive.  In that case, the barycenter will probably be located somewhere inside the more massive object.  This is the case for the Earth and her Moon.  Based on numbers I got from Wikipedia, the Earth-Moon barycenter is about 1000 miles (1700 km) beneath Earth’s surface.  Or to measure that a different way, the barycenter is about 3000 miles (4600 km) away from the center of the Earth.

Now let’s say you have two celestial bodies of roughly equal mass.  In that case, the barycenter will be located somewhere between them.  Something like this has happened with Pluto and his giant moon, Charon.  Once more using numbers from Wikipedia, it looks like the Pluto-Charon barycenter is about 500 miles (960 km) ABOVE the surface of Pluto.

As for the Earth-Sun barycenter, it’s located deep inside the Sun.  So if you say Earth orbits the Sun, you’re not too far from the truth.  But of course Earth is not the only planet in the Solar System, and when you consider the Solar System as a whole, you’ll find the Sun wibbles and wobbles about in weird, loopy patterns.  As you can see in the highly technical diagram below, the Sun wibbles and wobbles so much it can wobble into a totally new position in just a few years.

Click here for an actual diagram of the Sun’s movement relative to the Solar System’s barycenter.

As explained in this paper, this is mainly due to the gravitational influences of Jupiter and Saturn. Over longer time scales (centuries rather than decades), the subtler influences of Uranus and Neptune also have a noticeable effect.

So the next time someone tells you the Earth orbits the Sun, you can do the “um, actually” thing and explain what a barycenter is.  Trust me, it’s a great way to sound smart and make lots of new friends!

Next time on Planet Pailly, what did people in 1962 think we’d find on other planets?

Sciency Words: Nominal Solar Radius

Sciency Words: (proper noun) a special series here on Planet Pailly focusing on the definitions and etymologies of science or science-related terms.  Today’s Sciency Word is:


Last week, I told you about the classification system in use for main sequence stars. Today we’re going to talk specifically about G-type stars.  Or rather, we’re going to talk about one G-type star in particular: the Sun.

I was recently clued in on a controversy about the Sun.  After reading up on the issue, though, I don’t think this is a real controversy.  It’s more like an Internet controversy.

If you’ve ever wondered how big the Sun is, a quick Google search will get you an answer.  But it won’t get you the correct answer.  That’s because we apparently do not know precisely how big the Sun is.  As this paper from 2018 states: “[…] measuring with high accuracy the diameter of the Sun is a challenge at the cutting edge of modern techniques.”

Part of the problem is that we’ve tried using multiple methods for either measuring the Sun’s radius by direct observation or by calculating the radius based on other kinds of measurements.  And we keep getting different answers.  I take it we’re not getting wildly different answers, but there’s enough variation there to create a problem for scientists who study the Sun.

So here’s where the alleged controversy comes in.  Our friends at the I.A.U.—the International Astronomy Union, the same organization that decided Pluto is not a planet—decided a few years ago what the Sun’s radius should be.  They said it equals 695,700 km.  No more, no less.  I mean, who are these people to decide what is or is not a planet?  Who are these people to decide now how big the Sun is?

Except that’s not actually what the I.A.U. did. Regardless of how I may feel about the whole Pluto thing, I do agree with the I.A.U. about their definition of the solar radius.  Or to speak more precisely, I agree with their definition of the nominal solar radius.  As explained in the I.A.U. resolution on this matter:

These nominal values should be understood as conversion factors only—chosen to be close to the current commonly accepted estimate […] not as the true solar properties.  Their consistent use in all relevant formulas and/or model calculations will guarantee a uniform conversion to SI units.

So I don’t think the controversy, such as it is, really exists.  If we’re going to use the nominal solar radius as a unit of measure, we all have to agree about what that unit of measure is equal to—especially because we still don’t know what the actual solar radius is.

Feel free to bash the I.A.U. about Pluto, if you want, but when it comes to their nominal solar radius definition, I think the way they handled it makes a lot of sense.

Art in the Wild: Mr. Sun

Of late, I’ve felt that I need to push myself a little harder with my art.  I’ve been doing lots and lots of drawings, so it’s not that I’ve gotten lazy; rather, I feel like I’ve gotten complacent.  I feel like I keep doing the same kind of drawing over and over again, without really challenging myself or stretching my artistic skills.

So to shake up my routine, I decided to take some of my art supplies “out into the wild,” so to speak.  Or at least I took them out of my art studio and brought them with me to my day job.  My hope was that I could draw something based on first hand observation, rather than from photo references, mannequins and maquettes, or pure imagination.

A year or two ago, a thoughtful friend left this Mr. Sun figurine on my desk.  Given the history of this blog, that seemed like a good place for me to start.

One of the challenges of drawing from first hand observation is that your mind plays tricks on you.  You have to get past what your mind thinks you should see and draw what your eyes actually see. I had a really tough time with this drawing because my mind kept insisting there should not be highlights and cast shadows on the Sun; the Sun is supposed to be a light source!

It’s been a long time since I’ve taken my art out of the studio like this.  I think it was good practice artistically speaking, and a surprisingly difficult mental challenge as well.  I plan to do a whole lot more of this.  Let me know in the comments if you’d like to see more of the results (good, bad, or ugly).

I love drawing almost as much as I love writing.  But when you love something, there’s a real danger of settling into a comfort zone, becoming complacent, and getting bored. And then you may start to fall out of love with that thing (or maybe even that person) that you loved so much.

So whatever it is you love, I hope you’ll keep pushing yourself, take some risks, and challenge yourself to do something more with it.