…or is it?
Here are some objects which may or may not be moons, shown to scale. Enjoy!
Organised by diameter:
Endor – 4900 km
Mercury – 4879 km
Luna – 3474 km
Pluto – 2377 km
Tethys – 1062 km
Ceres – 946 km
Starkiller Base – 660 km
Miranda – 472 km
Vesta – 530 km (mean)
Enceladus – 504 km
Mimas – 396 km
Death Star II – 200 km
Death Star – 160 km
The Universe really is quite pretty and mathematical. It’s just full of natural rhythms and geometries, and this is often apparent in the orbits of stars and planets.
Planets like to be in harmony, tugging each others orbits with gravity and falling into resonances where their orbits have perfect integer ratios. A nice little illustration of this is the Moons of Jupiter, shown in this animation.
Io, Europa, and Ganymede have a perfect 1:2:4 resonance (formally referred to as a Laplace resonance), where the timing of Europa’s orbit is twice that of Io, and the timing of Ganymede’s orbit is twice that of Europa. I find it really quite satisfying to watch.
In theory, objects in stable orbits around the same celestial body tend to find resonances like this – in practice, you tend to find a mix of perfect resonances which are stable and long term, like Jupiter’s moons above, with other apparent resonances being seemingly coincidental⭐. The orbital ratios we see may be nice and tidy, like Mars and Earth which have an apparent 1:2 ratio, or they might be more unusual, like Neptune and Saturn with their 5:28 ratio. But perhaps the most interesting thing is the shapes these orbits can trace out.
Earth and Venus currently have an 8:13 orbital ratio, which means Venus completes 13 solar orbits every 8 Earth years, with the two planets passing close to each other 5 times for each set of orbits. And if you link the two with an imaginary straight line, it traces a rather lovely pattern.
The centre point of that line draws a cherry blossom! 🌸
Again, you can do the same thing for any pair of planets, ending up with a pattern reminiscent of spirographs, mathematical roses, or possibly higher dimensional uniform polytopes.
Here are a few more!
These images were sourced from a page by Ensign Software.
⭐ I’m not really fond of talking about coincidences where science is concerned, but that appears to be the case here. The perfect “mean motion resonances” are relatively rare, with most observed orbit ratios being “coincidental near-resonances” which appear temporarily stable but gradually shift over time. In other words, they appear to be in resonance over short timescales of hundreds to thousands of years, but on astronomical timescales they’re effectively random. Which means things like the apparent 8:13 Earth Venus ratio are actually an illusion. But shhh, you’ll spoil the mathematical prettiness.
Wormholes show up a lot in fiction, don’t they? I’ve seen the concept reiterated several times in various different ways, in everything from obscure sci fi novels to high budget movies. Which makes sense really, because it’s a compelling idea, particularly in a universe where everything tantalisingly nearby is actually surprisingly far away, and the maximum speed limit of physical objects in our Universe is disappointingly slow⭐.
This article discusses Interstellar, Thor, Thor Ragnarok, and The Avengers, but any spoilers are mild at best.
I do admire Neil deGrasse Tyson for his work in science communication, particularly for bringing some much needed diversity to a profession which still sorely needs it. However, he does have… shall we say, a certain proclivity for pedantry.
This afternoon, I stumbled across this on twitter:
It’s true. Neil has a strange fixation with this phrase and seems to pin all of the blame on Pink Floyd.
It’s certainly become something of a running joke at this point, that Tyson likes to “well, actually” things like this. But he isn’t always right, even on little crusades which he’s evidently spent years championing.
The “dark side of the moon” thing seems to be a popular little phrase to argue about among people on the internet with too much time on their hands too, no matter how inconsequential it may be. At least one article I’ve written before ended up with a few “well, actually” comments being made.
Honestly, I dislike being needlessly pedantic, but sometimes you just need to fight meticulosity with meticulosity⭐. Fine. Let’s look at this.
The term “dark side of the moon” is older than you might realise and, in a good many old phrases, the exact meanings of the words may not be a perfect match with the modern usage with which you may be familiar📚. Languages are messy like that. In many cases though, older meanings still do exist in any given language and are perfectly valid in modern usage.
In this case, the word dark refers to the unseen or the mysterious. For instance, the Merriam-Webster dictionary defines one meaning of the word to be “not known or explored because of remoteness.” Originally, the word derives from an Anglo-Saxon word deorc, which in turn relates to an Old High German word terchennen (also pronounced/written derchennen), which means to hide.
So generally, this meaning of the word dark refers to things which are hidden, secret, or obscure🔮🍫, and have since at least Shakespearian times. A bit like, oh, I don’t know, a side of the Moon which we can never see from the surface of Earth.
We still only rarely see the dark side of the Moon. Not many spacecraft have been there, and not all took any photographs. It wasn’t until 1959 when the Soviet Luna 3 probe send us the first images of the Moon’s outward facing surface.
So I mentioned it’s an old phrase. How old exactly? Well, it’s definitely older than Pink Floyd’s 1973 psychedelic prog rock album, that’s for sure.
There are various references to the term here and there in literature. An instance which some purport to be the first appearance in print comes from the Rural Visitor, a newspaper from New Jersey in the USA, published in 1810, stating:
“[People] may be found possessing great professional knowledge, much integrity, and yet be as utterly unnoticed as though they tenanted the dark side of the moon.”
The casual usage of the phrase here heavily implies that this was already a widely used phrase in the US back in 1810. Google ngram seems to agree on this.
The first use in literature is from the early 1700s, and there’s no way of saying how much the phrase may have been used prior to this. So slightly predating Pink Floyd, then.
Evidently, the two terms “dark side of the moon” and “far side of the moon” may be synonymous, but the former term is older and has always been more frequently used. It should be borne in mind though, that this may be swayed by this term having two meanings, refering both to the Moon’s far side and the side which is in shadow (the literal dark side).
More generally, the phrase “dark side” in English literature apparently dates back to at least the 17th century.
Something which gets said a lot, and for convenience I’m going to just overlook the fact that a sphere only has one single curved side.
The thing is, yes, we know this. We have known this for a long time. Leonardo Da Vinci studied the way shadows fell on spheres back in the 15th century, and while he may have been a particularly prominent (and rather interesting) individual, I doubt he was the first to do so.
From there, it doesn’t take a huge leap in logic to figure out that when the Moon appears dark from Earth, its far side must be bathed in sunlight. But the term in English is never used to refer to the side of the Moon which faces Earth.
And honestly, I’ve never understood why some people get their panties in such a bunch over this.
The phrase “dark side of the moon” is one which the overwhelming majority of native English speakers know. It also has a certain poetic charm about it, which is probably why Pink Floyd ended up popularising it. Ulimately, I’ve no problem with the evolution of language and time will tell which phrase ends up being the more popular of the two.
I suspect that once the Moon’s usually non-visible side becomes more well known to us, perhaps when we finally start sending astronauts back there, the term “dark side” will truly cease to have any meaning beyond in poetry. Then maybe we’ll see some more images like this gorgeous photo from Apollo 16 in 1972, where the camera was being held by an actual human as it was being used.
Until then, I see no particular reason to stop using it. Telling people that they’re wrong isn’t really good science communication, especially when you’re not actually correct. If you want to go on a crusade against common English words and phrases, fighting against the ones which are discriminatory would be a better place to choose your fights.
In summary…
I really doubt anyone’s “busy” with this, and I know I never have been. Using a common phrase is not damage. It was in use long before Pink Floyd. A sphere only has one side. The term refers to the metaphorical dark as opposed to literal darkness.
I’m just going to let Luke Skywalker sum up my feelings on Tyson’s tweet:
⭐ Yes this is a real word. “Meticulousness” sounds cumbersome.
📚 The changing meanings of words is all part of what makes a living language so vibrant, as certain words fall in and out of favour with the general population. This is why I make a point of not using words like “colony” or “settlement” due to unfortunate connotations which remain as a hangover from colonialism – and despite what some might believe, connotations are an important part of a word’s meaning which often lie outside the dictionary definitions. Where there’s a word to use without negative historical connotations, it seems far more logical to use that. But that’s a post for another time…
🔮 As an aside, the fact that dark has also come to mean sinister in English is probably responsible for all kinds of unfortunate associations. For instance, “the dark arts” is a term any fans of Harry Potter will know. It’s actually older than the term “dark magic” which has come to be synonymous with it. I suspect it’s quite likely that “dark arts” originally meant something more like “unseen arts” because people believed in folklore to use magic would presumably do so away from public view.
🍫 As a second aside, dark also has a dictionary-defined meaning of “posessing depth or richness” which I rather like. It’s quite evocative of things like dark chocolate, black coffee, and other complex flavours. Merriam-Webster’s lovely example of “a dark voice” makes me feel like we should use this meaning more in common English.
So I may have spend some of my idle brain and CPU time yesterday making paperclips. Wait! I promise this is more interesting than it sounds!
The game Universal Paperclips, shown to me by a friend (thanks Wil!) after my Dangerous AI article, sees you take on the role of an AI whose existence has one simple goal. Make paperclips.
It starts off as you might expect. You have to balance costs and earnings, create better manufacturing equipment, improve efficiency and so on. Up until the point where you take over the world, learn how to process any kind of matter into paperclips, learn how to make machinery out of the paperclips themselves, an ultimately dismantle the entire planet and turn it into paperclips. Then, once you’ve finished demolishing the Earth, your raison d’être continues by exploring space with the ultimate goal of turning all matter in the universe into paperclips. Obviously.
While not a game to focus all your attention on, it’s amusing to have running in a background window. As I write this, my self-replicating probes have explored 0.000053646601% of the Universe and are creating 258.9 quattrodecillion paperclips per second. Feel free to speculate on how they’re stored in order to prevent them from spontaneously collapsing into black holes due to their high iron content. I’m not sure quite what makes this game so addictive when, involving little more than numbers and idle clicking, it should be tedious by all rights. Perhaps it just amuses my inner evil scientist.
Interestingly, there’s a serious background to this odd little game. It’s based on the Paperclip Maximizer a thought experiment by Nick Bostrom, a Swedish philosopher, dating back to 2003. The point to it is illustrating the potential existential risk which could result from an artificial intelligence with a seemingly innocuous goal. While it may have no inherent malice in its intentions, its actions could pose a threat if allowed to spiral out of control. In this case, if its sole goal is to create as many paperclips as efficiently as possible, it could be justified in its decision that humans are unnecessary. Likewise planets, stars, galaxies…
In he 2008 book Global Catastrophic Risks, AI researcher Eliezer Yudkowsky wrote a chapter entitled Artificial Intelligence as a Positive and Negative Factor in Global Risk. He summed up the concern succinctly:
❝ The AI does not hate you, nor does it love you, but you are made out of atoms which it can use for something else.❞
Eliezer Yudkowsky
The idea is, of course, hyperbole. Bostrom didn’t genuinely believe that a rogue AI might turn the Universe into paperclips (hilarious and horrifying though that might be), rather this is an example of a hypothetical phenomenon dubbed Instrumental Convergence.
That term may seem a little opaque, but it’s fairly simple really. Basically, any intelligent agent, human or otherwise will have a set of goals when attempting to accomplish something. A final goal, containing the intended end state, and a set of intrumental goals which are required to get to that end state. For example, I currently have a final goal of writing a blog post, which requires several instrumental goals such as organising my thoughts, typing sentences, structuring them into paragraphs, creating a logical narrative, etc.
❝ Several instrumental values can be identified which are convergent in the sense that their attainment would increase the chances of the agent’s goal being realized for a wide range of final goals and a wide range of situations, implying that these instrumental values are likely to be pursued by a broad spectrum of situated intelligent agents.❞
Nick Bostrom
Going back to the hypothesis, instrumental convergence is the idea that whatever an intelligent agent may set out to do, its most basic instrumental goals may tend to be very similar. At a fundamental level, you could consider them to be analogous to the instincts found in animals. All animals have a set of basic instrumental goals, like avoiding danger, eating enough food to survive, reproducing, continuing to breathe, and so on. For an AI, we’re off the edge of the map, but a few basic AI drives have been proposed, including utility function, self-improvement, freedom from interference, unbounded acquisition of resources, and self-preservation.
Linking back to my Astrotropes post, this idea has been explored in fiction too. The 2014 movie Transcendence features an AI which takes on all of these basic values. The result is unsettling. So could a situation like this actually occur? The answer is, we genuinely don’t know.
I’d argue that two of those proposed AI drives are actually quite human in origin and may not necessarily apply to an artificial intelligence.
When you think about it, unbounded acquisition of resources isn’t logically necessary for all purposes, and even where it is a goal, it may not necessarily mean the same as acquire all available resources by any means. I’d suspect that living in a capitalist society where acquisition of material wealth is the main driving factor might skew our perspective on this. If your goal is to manufacture as many paperclips as possible, then acquiring as much matter as possible is a logical solution. For most other purposes, it seems more likely that an intelligent agent may wish to acquire precisely as many resources as necessary and no more.
Freedom from interference too, sounds like the kind of thing a comic book villain might request, but it seems unlikely to be something an AI might require unless it was proven to be a necessity. And even then, particularly if utility function is a basic AI drive, it seems unlikely that an AI would enact any dangerous or apocalyptic feats to accomplish it. That would be an unnecessary and illogical waste of effort and resources which could be better used elsewhere. To quote GLaDOS in Portal 2, “The best solution to a problem is usually the easiest one. And I’ll be honest, killing you is hard.”
Some people take the ideas of instrumental convergence to mean that we should try to make certain that an AI has implicitly human values to prevent it from doing harm. I’d add that giving it a purpose which is more nuanced than simply “do as much of this as you possibly can” would probably be a good idea too. As any good coder will tell you, infinite loops are best avoided. In any case, thought experiments and instrumental convergence aside, I’m still not convinced that artificial intelligence is the great existential threat that so many people seem to think it is.
At least, unless paperclips are involved. Then we’re clearly doomed.
This trope may not be particularly astro-related, but it’s nonetheless quite ubiquitous in science fiction, both in space and on Earth. For a long time, humans have daydreamed about the ability to create artificial intelligence (AI) which may be equal to us, or even surpass us. But as technology increases to the level where it’s starting to seem like a possibility, it seems our paranoia about the idea is steadily increasing.
Particularly in recent years, a lot of fiction focussing on AI seems to be full of themes centred on moral dangers, othering, and generally portraying AIs as being a danger to us. This is not being helped by influential figures like Stephen Hawking and Elon Musk stoking our paranoia in the real world.
This article discusses, and contains some pretty major spoilers for, Star Trek: The Next Generation (Episode 1:13, Datalore), Prometheus, Alien: Covenant, Ex Machina, Portal, 2001: A Space Odyssey, the Terminator movies, the Matrix movies, and Frankenstein.
Inspired by that last Astrotropes post of mine, here is a very circular graphic showing kinetic energies of various things, fictional and non-fictional. Go and check the other post for some more details, and mind out for any spoilers.
Essentially, there are only two types of energy in the universe. Kinetic energy and potential energy. Moving objects (like asteroids and tennis balls) have kinetic energy, and if a moving object strikes something, that energy is transferred. Pretty much everything also contains potential energy, waiting to be released. That could happen by detonating it, in the case of a stick of dynamite, or by eating it in the case of a doughnut. Also, a doughnut contains more potential energy than a stick of dynamite! How wild is that!
The sizes in the graphic are scaled logarithmically. Double the size means 10 billion (1010) times as much energy. Which makes some things a little tricky to discern, but it was the only realistic way to fit a black hole collision and a cosmic ray particle on the same graphic. I mean, I tried a linear scale, but, well…
So yeah, a black hole collision releases about a hundred thousand million trillion trillion trillion⭐️ times as much energy as a cosmic ray particle, and I figure most people don’t have screens that large.
Also, yes, the most energetic cosmic ray particle ever detected was nicknamed the OMG particle. With good reason too. A single proton travelling at 99.99999999999999999999951% the speed of light, and consequently carrying the same energy as a baseball is not the kind of thing we normally detect here on Earth!
⭐️ This sounds like hyperbole, but it’s really not. That particle was travelling with 48.07 J of energy, while two colliding black holes release 5.39 × 1047 J!
High above Earth, several United Federation starships are locked into a desperate battle against a Borg cube. On the bridge of his ship, Worf hears a grim damage report. His blood boils and he slams a console with furious fists. “Perhaps today is a good day to die,” he growls, before barking an order to his surviving crew. “Prepare for ramming speed!”
This post is loaded with massive (and high velocity) spoilers for Star Wars – Rogue One, A New Hope, Return of the Jedi, and The Last Jedi.
The above sequence with Worf fighting against the Borg, by the way, is from Star Trek First Contact. It’s not a spoiler because it happens in the first 5 minutes of the movie!
Space, as a background, is a mainstay of sci fi. But space is hazarous, and if you’re to find yourself without air to breathe, that should probably be cause for alarm. Naturally, sci fi characters (much like real life astronauts) go to great lengths to avoid this. “Don’t leave your spacecraft without a protective suit” is generally some rather sound advice. Unfortunately, in many stories, that isn’t always an option.
Caution: This post has mild spoilers for Star Wars VIII: The Last Jedi, Sunshine, Gravity, and episode 7 of Cowboy Bebop.
Happy Birthday Carl ❤️
Writing this blog is a labour of love, and one which I evidently need a little encouragement towards on occasion. If you like what I write, the best way to show your gratitude would be to fuel my caffeine addiction and buy me a coffee to say thank you. All coffee donations are gratefully accepted!
Never stop dreaming...
Supernova Condensate 
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