Mercury A to Z: Vulcan

Hello, friends!  Welcome to another posting of the A to Z Challenge.  For this year’s challenge, my theme is the planet Mercury, and in today’s post, logic dictates that V is for:


As you know, Mercury is the planet closest to the Sun, but at one time astronomers had reason to believe that there was another planet even closer to the Sun than Mercury.  This hypothetical planet was named Vulcan, after the ancient Roman god of fire—a highly logical choice.

Our story begins with Isaac Newton and his law of universal gravitation.  Thanks to Newton, it became possible to predict the motions of the planets with extraordinary precision; however, in the centuries following Newton’s death, astronomers started having trouble using the logic of Newton’s law to predict when transits of Mercury would occur.

A transit of Mercury is when Mercury passes directly in front of the Sun, as observed from Earth.  This is one of the most exciting ways to see Mercury, provided you take the necessary precautions to protect your eyesight.  But in the 18th and 19th Centuries, Mercury started transiting the Sun at seemingly illogical times.  Mathematical predictions of Mercury transits were off by minutes, hours, or even by as much as a full day!

So French astronomer and mathematician Urbian Le Verrier hypothesized that another planet (named Vulcan) might exist, orbiting the Sun within the orbital path of Mercury.  Vulcan’s gravity might perturb the orbit of Mercury enough to explain why Mercury never seemed to transit the Sun on schedule.  Le Verrier had made a similar hypothesis, based on perturbations of the orbit of Uranus, which led to the discovery of the planet Neptune.  Thus, it seemed only logical to take Le Verrier’s Vulcan hypothesis seriously.

In the following years, a few astronomers claimed to have found Vulcan, proving Le Verrier’s hypothesis, but follow up observations could never confirm these discoveries.  Most sightings of Vulcan were probably just stars that happened to be near the Sun.  Most transits of Vulcan were probably just sunspots.  Perhaps, instead of a single planet, Vulcan might be a swarm of asteroids: the vulcanoid asteroids.  But it would require an absurd number of asteroids to account for the observed perturbations of Mercury’s orbit.  Logically speaking, an asteroid swarm that large would have already been noticed.

So Mercury kept transiting the Sun at the wrong times, according to Newton’s laws, and no one could explain why.  Not until 1915, with the publication of the theory of general relativity.  Thanks to the logic of German theoretical physicist Albert Einstein, we now know that the mass of the Sun curves the fabric of space-time.  This curvature affects the orbits of all the planets, but most especially the orbit of Mercury, because Mercury is so very close to the Sun.


Today I want to recommend this video from Astrum, one of my favorite YouTube channels.  If you love space as much as I do, it would be only logical to check out what Astrum has to offer.

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.”

Sciency Words: Newtonmas

Hello, friends!  Welcome to Sciency Words, a special series here on Planet Pailly where we talk about science or science-related terms.  In today’s episode, we’re talking about:


Newtonmas is often described as a secular alternative to Christmas.  Some people see Newtonmas as an affront to Christmas and all things Christian.  Me?  I don’t believe science and religion necessarily need to be adversaries, and I don’t see any reason why we can’t celebrate two things on the same day.

Newtonmas commemorates the fact that Isaac Newton was born on Christmas Day, 1642.  Or at least that’s Newton’s birthday according to the Julian calendar.  According to the Gregorian calendar, Newton was born on January 4, 1643.

If I may wander into the calendar technicality weeds for a moment, the Gregorian calendar was first introduced in 1582, but it was not adopted by all countries right away.  Great Britain didn’t switch over until 1752.  And so at the time of Newton’s birth (1642/1643), in the place where he was born (Lincolnshire, England), the Julian calendar was still in effect, and it remained in effect for Newton’s entire lifetime.  So as far as Newton and his countrymen were concerned, he was born on December 25, 1642.

The first documented celebration of Newtonmas occurred in Japan.  In the late 1800’s, a small group of students at the Imperial University in Tokyo formed an Isaac Newton fan club.  This fan club rapidly grew in popularity and soon included a mix of undergrads, grad students, and professors.

And so on Christmas Day, 1890 (Gregorian calendar), members of this Newton fan club got together for the first ever Netwonmas party.  According to this article from the time, the party included humorous science lectures, a science-themed gift lottery, and plenty of “laughter and good cheer.”  Basically, Newtonmas started out as nerdy fun.  And as far as I’m concerned, that’s what it still is (and I do not want to hear any “war of Christmas” nonsense in the comments, thank you very much).

So merry Newtonmas, friends!  And merry Christmas, too!  There’s no reason you can’t celebrate both, if you want to.

P.S.: This will be my final blog post of 2020.  I’m taking some time off for the holidays.  I’ll see you again, friends, on January 6, 2021 (Gregorian calendar) for the first IWSG post of the New Year.

Inverted Space (Tomorrow News Network: A to Z)

Hello, friends, and welcome back to the A to Z Challenge.  For this year’s challenge, I’ve been telling you more about the universe of Tomorrow News Network, my upcoming Sci-Fi Adventure series.  In today’s post, I is for:


On ancient Earth, there were three great revolutions in physics.  First came Isaac Newton and his laws of classical mechanics.  Then came Albert Einstein with his theories of special and general relativity.  And lastly, near the end of the 21st Century, Dr. Harold Strickland published his theory of inverted space.

In the simplest possible terms, inverted space is a place where the laws of physics are reversed.  It’s a universe of anti-physics, if you will.  Dr. Strickland believed that in order for our universe to exist as it does with the laws of physics that it has, then an equal and opposite universe must also exist to create balance.

One might expect such a radical and bold theory to spark debate and controversy among the scientific community.  It did not.  Few took any notice of Strickland’s work at the time.  It wasn’t until many years after Strickland’s death that he received the recognition and credit he deserved.  What changed?  The discovery of faster-than-light technology.

You see in our universe, nothing can travel faster than the speed of light; in inverted space, nothing can travel slower than light.  Of course, jumping into inverted space is dangerous.  The laws of physics are reversed, after all.  The attractive forces that hold atoms and molecules together become repulsive forces.  Molecular and atomic decoherence can occur within seconds!

But a quick jump in and out of inverted space is relatively safe, and a sequence of quick, carefully calculated “inversions” can allow a spacecraft to cross the vast distances of the galaxy.

It’s also worth noting that in inverted space, time runs backwards instead of forwards.  This troubled Dr. Strickland, yet it was an unavoidable consequence of his math.  If you were to jump through inverted space and then jump back to your starting location, would you not arrive before you departed?  Would this not violate causality and create a time travel paradox?

As it turned out, nature has its own ways of preventing paradoxes, even if Dr. Strickland couldn’t find them in his math.  When you push two magnets together, either positive to positive or negative to negative, the magnets resist.  They repel each other, and the harder you try to push them together, the harder they push back.

Something similar occurs in inverted space.  If you jump through inverted space and then attempt to jump back to your original location, your spacecraft will be deflected off course.  Your past and present selves seem to repel each other, like magnets, and so this is known as the chronomagnetic effect.

Nothing in the theory of inverted space predicted this chronomagnetic effect would exist, and nothing about the theory of inverted space can help explain why it occurs.  So while inversion theory is more advanced than relativity theory or classical mechanics, it still does not provide a complete picture of how the universe works.

For a complete picture of how the universe works, you’d have to learn about chronotheory, the science of time travel.  And next time on Tomorrow News Network: A to Z, we’ll talk about the people who use chronotheory to bring you tomorrow’s news today.

Sciency Words: The Anomalous Precession of the Perihelion of Mercury

If you’re anything like me, you’ve probably looked at planetary orbits and asked yourself: why does Mercury’s perihelion precess so anomalously? That simple, straightforward question is the subject of this week’s edition of Sciency Words.

Sciency Words is a special series here on Planet Pailly where we take a look at a new and interesting scientific term so we can all expand our scientific vocabularies together. Today’s term is:


I know, it’s a bit of a mouthful, but trust me… this anomalous precession thing is pretty cool.

Gravity According to Newton

Back in the 17th Century, Isaac Newton found a mathematical way to describe gravity, and his mathematical description worked for everything from falling apples to the orbits of all the planets. Well, all the planets except Mercury.

Mercury’s perihelion (the point where Mercury is as close to the Sun as it gets) moves.  That in and of itself isn’t so strange, but the perihelion moves a tiny bit faster than it should according to Newton.
Mercury’s perihelion (the point where Mercury is as close to the Sun as it gets) moves. That in and of itself isn’t so strange, but the perihelion moves a tiny bit faster than it should according to Newton.

The mystery of Mercury’s orbit (or the “anomalous precession of the perihelion of Mercury,” to use the technical lingo) baffled scientists for centuries. That is until Albert Einstein came along.

Gravity According to Einstein

Einstein’s theory of general relativity postulates that space and time are not separate entities but two aspects of what physicists now call space-time. General relativity predicts that the force of gravity causes space-time to bend or warp.

Needless to say, the Sun has a lot of gravity. Turns out that the warping of space-time around the Sun precisely explains Mercury’s weird orbit. In fact, every planet experiences some degree of this anomalous perihelion thing. It’s just that, because Mercury is so much closer to the Sun, the warping effect is significantly more noticeable.

Fe12 Time Warp

This is perhaps the planet Mercury’s greatest contribution to science. The anomalous precession of Mercury’s perihelion provided one of the earliest proofs that general relativity—and all the wibbly-wobbly, timey-wimey stuff that comes with it—is not just science fiction.

Fe12 Albert and Isaac


The 200-Year-Old Mystery of Mercury’s Orbit—Solved! from io9.

The Mysterious Orbit of Mercury from The Great Courses.

Accounting for General Relativity at Mercury from The Planetary Society.

Artsy Science: Newton’s Waste Book

Artsy ScienceToday’s post is part of a collection of posts on the artistic side of science.  Through both art and science, we humans try to make sense of the world around us, and the two fields have a lot more in common than you might expect.

* * *

It’s the 17th Century.  Paper costs a small fortune, and young Isaac Newton receives a valuable gift from his recently diseased stepfather: a notebook.  Only the first few pages have been used.  The rest are blank.  So what does young Isaac decide to do with this precious treasure?

The prudent choice would be to save it for something important.  Perhaps some groundbreaking discovery that would have changed the way we view the whole world.  Instead, the idiot named this notebook “the waste book” and wasted it on trivial nonsense.

Newton filled his waste book with information about art, music, alchemy, mathematics, theology, science, philosophy… pretty much anything.  The book’s contents were so random and disorderly that, following Newton’s death in 1727, the book was marked “not fit to be printed.”

But in that mess of scribbly handwriting, we can find the first hints of Newton’s genius and the profound discoveries he was about to make.  By not treating paper as something sacred, he allowed himself to play with new ideas.  Perhaps he named his notebook the waste book to remind himself that the pages were to be “wasted” even on thoughts that might at first seem silly.

Isaac Newton

So the next time you sit down with a blank piece of paper, waste it on some trivial nonsense.  You have no excuse not to.  Paper is a lot cheaper today than in Newton’s time.  And if you waste enough paper, maybe… just maybe… you’ll stumble upon an idea that will change the world.

P.S.: It may not be fit for printing, but the waste book is available to the public for free online.  Good luck reading Newton’s handwriting, though.