Sciency Words: Supermoon

Hello, friends!  Welcome to Sciency Words, a special series here on Planet Pailly where we talk about the definitions and etymologies of science or science-related terms.  Today’s Sciency Word is:

SUPERMOON

I was recently part of a comment thread over on Scott’s Sky Watch.  We were talking about the term supermoon, along with other weird moon names like wolf moon, blood moon, harvest moon, corndog moon, flower power moon, gingivitis moon… you get the idea.  After that, I thought a Sciency Words post on “supermoon” was in order.

The term supermoon was coined by American astrologer (repeat: astrologer, not astronomer) Richard Nolle.  The term first appeared in an article Nolle wrote in 1979 for Horoscope magazine.  To quote Nolle himself from this 2011 webpage article, the term supermoon describes:

[…] a new or full moon which occurs with the Moon at or near (within 90% of) its closest approach to Earth in a given orbit.  In short, Earth, Moon and Sun are in a line, with Moon in its nearest approach to Earth.

This particular alignment of the Sun, Moon, and Earth is also known as a syzygy-perigee.  Perigee means the point when as object orbiting Earth comes closest to Earth, and syzygy refers to the straight line alignment of three celestial objects.

A syzygy-perigee has a marginal effect on Earth’s tides, and if the Sun and Moon are on opposite sides of the Earth (as depicted in the highly technical diagram below), then the Moon will appear to be slightly larger and slightly brighter than normal in our night sky.  Astrologers would have more to say about supermoons, but from an astronomy perspective we’re pretty much done here.

Personally, I don’t really have a problem with the term supermoon.  When the full moon or new moon happens to be 90% closer to Earth than usual, that’s kind of neat.  Sure, the term started as an astrology thing, but there’s a long history of astrology concepts and terminology being borrowed by astronomers.  Supermoon is no different.

And supermoons do tend to get a lot of attention in the popular press.  I’ve had a lot of awesome conversations with people about the Moon and space and science in general that started because of a news report about the latest supermoon.  I think that’s great.  Anything that gets people to take an interest in science is a positive thing in my book.

On the other hand, a few of those conversations have ended with people asking me about their horoscopes, which is a bit disappointing.

Next time on Planet Pailly, please don’t hate anybody, not even the people who deserve it.

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:

BARYCENTER

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: Bunny Hopping

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:

BUNNY HOPPING

So yesterday I was reading up on the latest spacesuit design from NASA, and I came across a term that I don’t remember ever seeing or hearing before.  In this article from Space Daily, NASA Administrator Jim Bridenstine is quoted as saying: “If we remember the Apollo generation, we remember Neil Armstrong and Buzz Aldrin, they bunny hopped on the surface of the Moon.”

This left me wondering: do people really use the term “bunny hopping” to describe how Apollo astronauts moved about on the Moon?  I tried really hard to trace the etymology of this term.  I didn’t find much, but honestly, when you see clips like this one, it’s easy to figure out where the term came from.

In my previous research on this topic, I’ve seen this method of locomotion referred to as “loping-mode” or “skipping-mode.”  But sure, we can call it “bunny hopping” too.  So why did astronauts do this?

Well, there’s something about walking that most of us, in our daily lives, don’t realize: Earth’s gravity does some of the work for us.  When you take a step, first you lift your foot off the ground, then you extend your leg, and then… well, try to stop yourself at this point.  With your leg extended forward like that, you’ll find that your center of gravity has shifted, and you can feel the force of gravity trying to pull you through the remainder of your walk cycle.

So walking feels like a natural and efficient way for us humans to get around because Earth’s gravity helps us.  Take Earth’s gravity away, and walking suddenly feels awkward and cumbersome.  In lunar gravity, which is approximately ⅙ of Earth’s gravity, the Apollo astronauts found other methods of locomotion to be more comfortable, more natural.  In this clip, we hear audio chatter of astronauts disagreeing about whether “hopping” or “loping” is a better way to get around.

Personal preference seems to be important here, both in how astronauts “walked” on the Moon and in how they described the experience of this new kind of “walking.”

Getting back to the new spacesuits from NASA, the new design features a dramatically improved range of motion.  The next astronauts on the Moon will have a much easier time getting around, and according to Administrator Bridenstine there will be no need for bunny hopping.  “Now we’re going to be able to walk on the surface of the Moon, which is very different from the suits of the past.”

And that’s got me confused.  I’m really not sure what Bridenstine means by that statement because, as I just explained, it was the Moon’s gravity—more so than the spacesuits—that made Apollo era astronauts feel the need to “bunny hop” on the Moon.  The new spacesuits, with their improved range of motion, should help astronauts in the new Artemis program avoid gaffs like these…

But without altering the Moon’s gravity, I don’t see any way to avoid “bunny hopping.”

Sciency Words: The 90-Day Report

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:

THE 90-DAY REPORT

We recently celebrated the 50th anniversary of the Moon Landing. There’s been a lot of talk lately about the old Apollo Program, and also a lot of talk about the new Artemis Program, NASA’s next manned (and womanned) mission to the Moon.

But this is not a Sciency Words post about Artemis (I’m saving that for next week).  Instead, this is a post about the 90-Day Report and how it effectively killed NASA’s plans to return to the Moon in the 1990’s.  I think the story of the 90-Day Report provides some context for what may or may not happen with Artemis.

It was July 20, 1989—the 20th anniversary of the Moon Landing—when President George H.W. Bush announced America’s intention to return to the Moon and establish a permanent presence there.  This would be part of a strategy for America to push onward to Mars.  Following the President’s announcement, a special committee was formed to figure out how to make it all happen.  The committee’s findings were released in a document titled “Report on the 90-Day Study on Human Exploration of the Moon and Mars,” a.k.a. the 90-Day Report.

According to the 90-Day Report, NASA would need to build a huge amount of infrastructure in space.  If you’ve seen Stanley Kubrick’s 2001: A Space Odyssey, that’s basically what the 90-Day Report described: giant space stations, a multitude of space shuttles taxiing equipment and personnel to Earth orbit, and enormous interplanetary space cruisers to transport astronauts to the Moon or Mars.

And how much would this cost?  The 90-Day Report conspicuously didn’t say, but the most commonly cited estimate was $450 billion.  To put that in some context, NASA’s budget at the time was just over $11 billion (according to Wikipedia, numbers not adjusted for inflation).  As Robert Zubrin explains in his book The Case for Mars:

It is doubtful that any kind of program could have survived that price tag. Given its long timelines and limited set of advertised accomplishments on the road to colonizing space, which did little to arouse the enthusiasm of the space-interested public, the 90-Day Report proposal certainly could not.  Unless that $450 billion number could be radically reduced, the [Space Exploration Initiative] was as good as dead, a fact made clear in the ensuing months and years as Congress proceeded to zero out every SEI appropriation bill that crossed its desks.

A lot of people ask why we haven’t returned to the Moon since the days of the Apollo Program.  The 90-Day Report is a prime example of why.  “Too many cooks in the kitchen,” as a dear friend of mine likes to say.  Where President Kennedy set a singular, clearly defined goal for the American space program, President Bush handed the space program over to a committee, which came up with a very complicated, very costly list of ideas, which Congress was unsurprisingly unwilling in paying for.

To be fair, at least one idea from the 90-Day Report did come to fruition.  We did get a giant space station.  But that only happened as a result of an international partnership, which is (in my opinion) a model for how all future space missions should be done.

So with the memory of the 90-Day report in mind, next week we’ll talk about the Artemis Program.

We Chose to Go to the Moon

We choose to go to the Moon!  We choose to go to the Moon….  We choose to go to the Moon in this decade and do the other things, not because they are easy, but because they are hard; because the goal will serve to organize and measure the best of our energies and skills, because that challenge is one that we are willing to accept, one we are unwilling to postpone, and one we intend to win, and the others, too.

J.F.K., 1962

This weekend, we celebrated the 50th anniversary of the Moon Landing.  Much has already been written about this anniversary: about what the Apollo Program meant to the United States and to the world, about why the space program has struggled in the five decades since, about future missions that may or may not be happening.

I’m going to approach this from a different perspective, because as passionate as I am about space, there’s one thing I’m even more passionate about: writing.

I’ve blogged about this before: being a writer is a lot like running the space program.  For a writer, every small step forward feels like a giant leap.  But much like NASA scientists, writers have a tough time setting realistic budgets and deadlines for themselves.  And most significantly, there will always been doubters and naysayers who want to tell you what you’re doing isn’t pragmatic.  You’re wasting time and money.  Aren’t there other problems you should deal with first?  Writing can wait.

So today, if I may borrow the words of President Kennedy, I’d like to say this:

I choose to write my stories!  I choose to write my stories and do the other things (like marketing, blogging, etc), not because they are easy, but because they are hard; because that goal will serve to organize and measure the best of my energies and skills, because that challenge is one I am willing to accept, one I’m unwilling to postpone, and one I intend to win.

– J.S.P., 2019

Now that I’m thinking about it, you could plug just about any goal you set for yourself into J.F.K.’s Moon speech, and it’ll probably still work.  So in the spirit of President Kennedy and the Apollo Program, what do you choose to do?

P.S.: Oh, and much like the Moon Landing, there are weird conspiracy theories about writers too.

Sciency Words: Submoon

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:

SUBMOON

After my recent post about exomoons and trickster moons, a reader commented asking about moons with moons.  Honestly, I couldn’t think of any reason why that wouldn’t be possible, but I felt like it must be an extremely rare thing. Otherwise we probably would’ve found something like that in our own Solar System by now.

And according to this paper entitled “Can Moons Have Moons?” the answer is yes.  Theoretically, under certain circumstances, a moon could have a very, very tiny moon of its own.

It’s important to note, however, that for an object to truly be considered a moon, its orbit must be stable.  For example, there are multiple objects that are in temporary orbit around Jupiter, but since those objects are not expected to stick around for more than a few years, or maybe a few decades at the most, they are not included in the official count of Jupiter’s moons.

In most cases, a small object caught in orbit around a moon will have a very difficult time maintaining that orbit.  The gravitational attraction of the nearby planet will just keep tugging and tugging, stretching the orbital path into a wider and wider ellipse.  It won’t take long before the moon’s gravity can no longer hold the small object it captured.

But according to that “Can Moons Have Moons?” paper, if a moon is relatively large (like our own Moon) and orbits relatively far away from its host planet (also like our own Moon), and if there aren’t a whole lot of other moons around to make gravitational interactions complicated, then yes: that moon could have a moon in a stable orbit.  A very, very tiny moon.  Something asteroid sized.

The research paper I’m citing proposes calling the moon of a moon a submoon, but that’s not an official scientific term.  Not yet.  It probably won’t be until an actual submoon is discovered somewhere out there.  Until then, other terms have been proposed, like meta-moon, nested moon, grandmoon, and moonmoon.  Moonmoon seems to be the most popular choice on the Internet, probably because of the Internet meme.  Which means when the time comes the I.A.U. will almost certainly not pick that one.  More likely, the I.A.U. will go with “dwarf moon” and insist that no further discussion of the matter shall be permitted.

For right now, I think submoon is the term with the most scientific legitimacy.  For the purposes of Sciency Words and other sciency writings, I think that’s the term to go with.  But what do you think?  What would you call the moon of a moon?

Putting STEM into the Arts

I thought I was done talking about the whole STEM vs. STEAM debate, but then it occurred to me that there’s one point that nobody seemed to be talking about.  This debate is often framed in terms of how the arts can benefit STEM.  No one ever seems to mention how STEM can benefit the arts.

About a month ago, SpaceX announced that Japanese billionaire Yusaku Maezawa will be going on a tourist trip around the Moon. Maezawa is an art collector, and he’s decided to take six to eight artists with him on a mission called “Dear Moon.”  According to the Dear Moon website, “A painter, musician, film director, fashion designer… Some of Earth’s greatest talents will board a spacecraft and be inspired in a way they never have been before.”

Art is meant to reflect the world we live in. Therefore artists have a responsibility to understand, as best they can, our increasingly scientific and increasingly technological world.  It sounds to me like Maezawa gets this.  But aside from seeking out new sources of inspiration, there are also craft-related reasons why artists might want to be exposed to sciency stuff.

As an artist, when you’re thinking about how light and shadow play off a three-dimensional form, you’re sort of thinking about physics. When you’re mixing paints, trying to make sure they’ll adhere to your canvass, or trying to make sure the colors won’t fade over time, you’re dabbling in chemistry.  And obviously when you’re drawing a figure study (nude or otherwise), knowing a little about anatomy and biology will help you a lot.

None of the art teachers I had in school, and none of the art tutors my parents hired for me outside of school, really made this clear to me.  As I said in my post on Friday, young me came to understand that the arts and sciences were totally different, unrelated things.  There was a long period of time in my life when I felt artistically stuck. I was unable to improve, and I didn’t understand why.

It wasn’t until I attended a seminar taught by James Gurney, the author and artist behind Dinotopia, that my art began to thrive again.  Why?  Because Mr. Gurney got me to start thinking scientifically about my art. I guess you could say he got me to stop thinking of myself as a left-brain-only kind of guy.

I can’t speak for every artist out there, but I know for me personally a more interdisciplinary approach to education would have done me a world of good.  And with that, I think I’ve said my peace about STEM and STEAM.  In my next post, I’ll move on to some other topic.

P.S.: While drawing that artist in space cartoon for today’s post, I thought of several reasons why painting in space like that would not work.  For one thing, I imagine those paints would do the whole freezing-and-boiling-at-the-same-time thing that other liquids tend to do in space.  If you can think of other challenges my artist/astronaut would have to deal with, please share in the comments!

How to Walk in Hypogravity

As a science fiction writer, I really wish I knew what it’s like to walk on the Moon or Mars or any other low gravity world.  It would help a lot with that whole “writing from lived experience” thing.  Of course there are ways I could experience hypogravity for myself, but I don’t have that kind of money.  So instead, I’ve turned to medical research papers like this one from Frontiers in Physiology.

First off, let me just say this: I’ve read some really complicated stuff over the years, but I don’t think I’ve ever read anything as complicated as a scientific paper trying to describe how we humans walk.

But if we want to understand what it would really be like to walk on another planet, we have to start by understanding—in meticulous mathematical detail, apparently—how we do this walking thing here on Earth.

Gravity Makes Walking So Much Easier

The mathematical relationship between walking speed, leg length, and gravity was determined back in the 1870’s.  It was later used in what sounds like a rather whimsical research paper about the walking pace of the Lilliputians from Gulliver’s Travels.  And then it was used for more pragmatic purposes to estimate the running speeds of dinosaurs.

For those sorts of calculations, the force of gravity would have been treated as a constant, but gravity can easily be treated like a variable, and that’s when things get interesting.  You see, when you walk, your body uses energy to complete the full arc of a footstep, especially at the beginning when you’re lifting your foot off the ground.  But gravity helps you (perhaps more than you realize) when your foot comes back down to the ground.

So if you reduce the force of gravity, gravity provides you with less assistance, and you end up having to expend more energy to complete each step in your walk cycle.

Walking-Mode vs. Running-Mode

The muscle actions involved in walking and running are different enough that there’s no real grey area between “walking-mode” and “running-mode,” as that paper from Frontiers in Physiology calls them. These two “modes of locomotion” take advantage of gravity in distinctly different ways.  Walking-mode ends up being more metabolically efficient at slower speeds, and running-mode is the more metabolically efficient way to travel at higher speeds.

So what happens when you alter the force of gravity?  The transition point where running-mode becomes more efficient than walking-more changes too. Lower gravity means your body will naturally want to switch modes at a lower speed.

On the Moon, for example, walking-mode only works well when you’re moving very slowly.  To achieve what we might consider a normal walking pace, you’ll have to switch to running-mode.  And if you want to reach Earth-like running speed, you’ll probably have to try hopping-mode or jumping-mode—modes of locomotion that we don’t use often here on Earth except under certain specialized circumstances. Skipping-mode also seems to be more metabolically efficient on the Moon than it is on Earth.

Moon-Walking or Mars-Walking in Science Fiction

I’ve read plenty of Sci-Fi stories set on the Moon or Mars. For the most part, I feel like science fiction writers just mention the reduced gravity thing in passing and then move on with the story as quickly as possibly.  I don’t blame them.  It’s really hard to imagine what hypogravity must feel like, and even harder to communicate that feeling to readers.

But one of my highest ambitions as a writer is to write something that makes you feel like you’re there on the surface of a hypogravity planet like Mars.  I want to capture that experience of “running in order to walk” and “hopping in order to run.”  Hopefully this line of research will someday help me pull that off.

Sciency Words: Thiea

Today’s post is part of a special series here on Planet Pailly called Sciency Words.  Each week, we take a closer look at an interesting science or science-related term to help us expand our scientific vocabularies together. Today’s term is:

THEIA

When I wrote about the Nice model, I said it does a nice job (pun intended!) of explaining how the planets of the Outer Solar System started out, and how they ended up where they are today.  But what about the Inner Solar System?  Well, it turns out we may have started with a few more planets than we have today, and one of those hypothetical early planets has been named Theia.

Technically speaking, Theia wouldn’t have been a planet (not according to the I.A.U. definition), but it was definitely planet-sized, perhaps as large as modern day Mars.  But Theia had to share its orbit with another planet that wasn’t technically a planet (yet): Earth.

Theia got stuck near one of Earth’s Lagrange points, about 60 degrees ahead of Earth in Earth’s almost circular orbital path.  There’s some weird gravitational voodoo going on at these Lagrange points, and so this arrangement of Earth and Theia could theortically have remained stable long term.

Except Jupiter and/or Venus disrupted the gravitational balance, pulling Theia a little this way, a little that way, nudging Theia away Earth’s Lagrange point and closer to Earth itself, until one day….

I would call this the worst disaster in Earth’s history, except this collision was sort of the moment when Earth (as we know it) really began.  I gather there’s still a lot of disagreement about the details, like whether this was a head-on collision or more of a glancing blow, but the two really important things to know are:

  • Theia knocked a large amount of Earth debris into space. That debris eventually coalesced to form our Moon.
  • Most of Theia is probably still here.Theia has become part of Earth, and the bulk of Theia may have would up becoming Earth’s core.

This idea that early Earth suffered a cataclysmic collision with another planetary body has been credited to a lot of different people, but it first appeared in the scientific literature in this paper from 1975.  The name Theia wasn’t introduced until much later, in this paper from 2000.

In Greek mythology, Theia was the Titaness who gave birth to the Moon.  That checks out. The name definitely seems appropriate.  In the myth, Theia also gave birth to the Sun.  That part doesn’t match up with the science so well.

But not to worry!  In next week’s episode of Sciency Words, we’ll meet the Sun’s real mother.