Follow the reluctant adventures in the life of a Welsh astrophysicist sent around the world for some reason, wherein I photograph potatoes and destroy galaxies in the name of science. And don't forget about my website, www.rhysy.net



Monday, 25 May 2015

Oh The Humanities !

The internet is awash with excellent articles on the importance of critical thinking, of how we judge evidence, confirmation bias, and all that jazz. In an age where so much depends on science, the importance of skeptical analysis has never been greater. But very recently I realised something that probably should have been blindingly obvious, but somehow wasn't.

I didn't learn critical thinking in University physics courses. I learned it in high school English.

That's perhaps quite a bold statement, so let me break it down a bit.

(First a note for international readers. In British parlance, "high school" generally means up to age 16, the limit of compulsory education (GCSEs). It can also overlap with "college", which is a term not often used but usually refers to education between the ages of 16 and 18 (A levels). Degree courses are almost exclusively taken at universities. Since college is such a rarely used term, I shall be referring to high school, A levels, and university.)


Science Education

I'd like to point out that I was the kid who accidentally lit the gas tap instead of the Bunsen burner. No, not the one who did it deliberately and claimed it was an accident. The one who actually did it accidentally and got the shock of his life.
Of course, I did learn about the scientific method in pretty much all science education, from primary school upwards. You can't have a science class that doesn't include the idea of formulating a hypothesis and testing it. But critical thinking was largely limited to being an implicit part of science education. In English, and to a lessor extent history, it's very much more explicit.

I want to make it quite clear that I don't want to belittle high school science education, which was totally solid. It certainly never forgot to emphasise the importance of having evidence to reach a conclusion or the importance of control experiments. But what it was lacking was the idea of critical, skeptical inquiry. This is perfectly sensible when you're dealing with things like equations of constant acceleration. Questioning them doesn't make any sense - it's far more important, and at that stage difficult, to understand the mathematics and work out how to use them correctly.

Things got a bit more unsteady during A levels, when you go from the idea of the atom as a miniature solar system to a much weirder notion of probability clouds of electrons which don't really exist. At that point you start to become aware that much of what you've been taught in science is a lie to children, a simplified version of the truth that's much more pedagogical* than it is literal. You can't teach 10 year olds quantum theory, you have to build up to it.

* No, I don't know how to pronounce it either.

Going into university, however, there's not all that much more development in terms of teaching skeptical inquiry. I'm not saying there was none - certainly the concept of a paradigm was explained, and there was a lot of explaining the evidence for contemporary ideas. Some courses did, very explicitly, get us to consider very alternative, non-mainstream ideas like panspermia, the Orion drive, and modified gravity. Most critically of all, we learned about statistics and selection effects. But generally, the focus remained on understanding equations and ideas.

Is that a good thing ? Generally, yes, though it really depends what you want to do with your degree afterwards.

At a PhD level things are different. You're compelled to think critically - though no-one actually teaches you - because you've got to test your own results to destruction. If you don't, if your analysis has a flaw then someone else is sure to spot it. And, hopefully, by experiencing the problems that occur and the imperfect solutions that sometimes have to be used, you come away with a much greater level of skepticism for everyone else's results too. Which does not mean you think everyone else is utterly gormless, only that you have a much better understanding of which bits of their results to trust and which bits you might want to question them about a bit more.




Oh, the Humanities !

Education in English (particularly literature), history, and PSE is an altogether different kettle of fish. I want to make it quite clear that I do want to belittle high school PSE and history education, which was, quite simply, utterly shite. To give an example : the existence of the British Empire was not mentioned. There's only one valid reaction to that.


I could wax lyrical on the horrors of British high school history education c1995-1999, but I'm not going to. Anyway while the attempt to actually teach us history - the story of how we came to be - was an omnishambles, it did do one thing very well. It taught us about the nature of proof and (primary and secondary) evidence. It taught us how to interpret evidence and how to critically assess it, how to form a conclusion based on data and (more implicitly) to be aware of the limits of the evidence.

Unfortunately it did so in the most ridiculous way possible, by randomly giving us assignments that had absolutely no connection whatsoever with what we'd previously learning about (e.g., the murder of Thomas Becket after several weeks of studying native American culture).

But, for all its many, many faults, history education did quite explicitly teach the importance of assessing evidence. PSE education was also dreadful, but in that case simply because the standard of teaching was abysmal. What they were trying to teach - morality, why we think some things are moral and some are not - was commendable, but PSE was treated very much as a "meh, who cares" subject by those in charge. Which was a shame, because when it was done well it taught us to examine our own beliefs and biases far more than any other course.

Fortunately, English lessons had none of the faults of history or PSE. We didn't spend a lot of time learning about nouns and pronouns and verbs and all that gubbins. Instead, we analysed things. We sought to understand what in the world Shakespeare was on about and why A Midsummer Night's Dream would have been oh-so-achingly-funny back in the day. We read contemporary poetry and tried to interpret it. Most pertinently of all, we analysed adverts and tried to assess how they were attempting to manipulate us. We were marked not so much on what our conclusion was, but in how well we were able to explain it and what evidence we had to support it.

English education covered something that science (at that level) simply could not : understanding what articles really mean, and what their intended effect is. When hearing someone expound the latest scientific theory, understanding if and how you're being manipulated is every bit as critical as understanding what the evidence itself suggests. That's something science classes never cover.

The humanities classes, then, form an essential part of teaching the scientific method - when they're done correctly. Being able to analyse a poem isn't the point - the point is you're taught to analyse meaning and assess implication. Or, in its simplest form, not to take things at face value.


Bad Astronomy


Or rather, bad science journalism. Given how good English lessons were at teaching critical thinking, the obvious question is : why are there so many bad science articles ? How come all these journalists seem to do such a dreadful job at explaining things to the public ?

One particular example really stands out. Without going into details, the acceleration of the Universe is thought to be increasing. An alternative idea has it that we're actually in a large void, which can mimic the effect of this acceleration. A few years ago a press release claimed that the void idea had been disproved*. On the very same day, another website used that same press release to pronounce that we do live in a void so there's no acceleration !

*I don't know if this has stood the test of time or not but it's not relevant here.

A more recent example : one press release claiming that dark matter is even darker than we thought, followed just two weeks later by one claiming that dark matter is not so dark after all. Ho hum. Neither of these is accurate. Nor is the one about a tidal wave in space, which is taking enormous liberties with what is already a highly ambiguous phrase.

If you read press releases quite often you're sure to recognize the following stock phrases :
- "Scientists baffled"
- "Mystery solved"
- "... than was previously thought".
"Now, researchers think they have the answer"
The last two are merely uninspiring. But from the first two, according to the media, scientists are either perpetually baffled or continually solving ever more complicated mysteries.

There are times when these phrases are appropriate. In astronomy the last really startling - baffling, if you will - discovery was that the Universe appears to be expanding faster and faster. That was seventeen years ago. Of course, less outrageous unexplained phenomena do come up all the time in science - because that's what it's there for. Any scientist who is in a continuous state of genuine bafflement is probably in the wrong profession, because not knowing the answer is the whole point of doing the job. You've got to be curious, but if you're going to just throw up your hands in bewilderment and say, "I just can't even..." then science isn't for you. Consider becoming an accountant instead, or take up golf.

Although why you'd want to do that is pretty baffling.
OK, "boffins baffled" is probably no more than a newspaper stock-phrase, much as politicians have "robust conversations". Much worse is the idea that scientists are continuously solving mysterious mysteries. Nothing could be further from the truth. Even disproving ideas is an extremely rare event, let alone proving what's actually going on.

Take, for instance, this recent article about galaxies being "strangled" (an accepted bit of jargon meaning removing their outer gas reservoirs) to death. It has the wonderful headline, "Murder Mystery Solved". Even from the press release it's clear that it's nothing of the sort :

"The scientists found that dead galaxies had much higher amounts of metals than live galaxies did. This finding is consistent with how strangulation would lead galaxies to evolve over time, Peng said."

Consistency isn't proof. It's consistency. That's why there are two completely different words that mean completely different things. Nothing in the article suggests they've ruled out any other ideas, yet the article also does nothing to clarify that the headline is, in fact, completely wrong.

Furthermore, reading most articles, one gets the impression that "scientists" are some sort of huge homogeneous group, and whenever a mystery is "solved" everyone is instantly content and moves on to something else (apart, presumably, from those unfortunate enough to be perpetually baffled). Of course outside this media fantasy land, proof almost never turns up, and trying to convince everyone that any one idea is better than another is a bit like trying to teach cats synchronised swimming.


Calling something "solved" when it's merely "more likely" isn't something I'd have been allowed to get away with in GCSE English, but it's de rigueur is mainstream science journalism.

The source of this sensationalism is hard to track down, and probably has a wide variety of causes. Most fundamentally, a lot of non-scientific problems are relatively easy to solve. Who was the killer ? Did a politician take a bribe ? Was the weather forecast accurate ? Will the construction project be on time and on budget ? "Real world"* problems like these at least can have decisive, clear-cut answers.

* A nonsense term considering that vastly more than 99% of the Universe is utterly uninhabitable to us. "Petty human world" would be better.

But it isn't like that in science, particular in astronomy where we can't fly off to distant galaxies to really check our answers. All we can do is make the best guess we can with the evidence we've got at the time. And that's not something you're really taught (in science or the humanities) until you study science beyond high school level. One would have hoped, though, that this is something science journalists would be aware of.

There's another, far more prosaic reason for sensationalism : it sells. Or more accurately, since not all news sites make a profit, it draws an audience (and yes, sometimes it's simply the scientists themselves clamouring for attention). Which naturally leads to clickbaiting : giving an article a title designed to elicit an emotional reaction strong enough that you're likely to click on a link. E.g., "These Ten Snuggly Kittens Will Restore Your Faith In Humanity", or "This Snuggly Kitten Went Outside And You Won't Believe What Happened Next"*. Being taught to recognize how you're being manipulated is a hair's breadth from understanding how to manipulate others**. Critical thinking is a double-edged sword.

* I have a sudden urge to write a post entitled, "Learn This One Weird Trick That Will Make Any Snuggly Kitten Teach You Astronomy".
** Also worth mentioning : even an article composed of nothing but facts can be manipulative. If I write an article comprised of nothing but anecdotes about reformed prisoners, you might come away thinking that the prison system is a model institution. If, however, I give you the larger statistics...

One final point : there seems to be a tremendous lack of interest in the journalistic world into actually bothering to check the press releases and get more details. While the sandwich-eating abilities of politicians are microscopically scrutinised by every news agency in existence, most science articles are little more than carbon copies of the press release. Which doesn't make a lot of sense because whenever anyone bothers to ask, it's very hard indeed to get most scientists to shut up about their research.

"I just get so lonely !"

Conclusion

Science education is great. English education is great too, though history education is dreadful. The humanities (when taught correctly) are at least as important in developing a rational, inquiring mind as science education is. School-level science has to be primarily about knowing facts and mathematical techniques; it's the humanities which provide a much better vehicle for teaching critical analysis at that stage.

But somewhere along the line something has gone badly wrong. Understanding what makes a good emotional article doesn't make for a good science article. Getting a lot of hits doesn't mean you've written a good article if your article is full of - literally - schoolboy errors. It just means you've written an article that got a lot of hits.

All too often, for a variety of reasons, science articles just aren't treated with the same level of respect or rigour that other stories are. Even mainstream media often simply regurgitate the information provided and stick the science article at the end of the programme : "... and that's how George the tortoise overcame his fear of toenail clippings. In other news, scientists announced a revolutionary breakthrough in solar power....". It's a weird phenomenon indeed when science is simultaneously trivialised and, paradoxically, sensationalised. There can be no clearer indication that science is not really understood.

Afterwards, George became a star on late-night SyFy channel movies.
Worse than this, even the official press releases - written by scientists in concert with a professional press officer - are sometimes able to use ridiculous terms like "tidal waves in space". When it gets to this stage, we've really got a problem. (Well, OK, it's not quite that bad - the press release was only using that as an analogy. To be fair the problem is almost entirely with secondary sources, e.g. the periodic reports about whether the Universe is a hologram - hint : it isn't.)

Some level of sensationalism is healthy. It's fun to speculate about the latest development in physics and where technology could take us. But we seem to have a culture of nothing but sensationalism, with some of the most popular (and high quality) science blogs being heavily devoted to debunking such nonsense.

A teacher once told me that the summer students we got at Arecibo were freaks of nature - meaning that they were the few for whom long tedious lectures were interesting. His point being that current teaching methods for science aren't a natural way for humans to learn. Perhaps we need to reconsider what we class as "dumbing down" and use more interesting, playful techniques to teach science, because clearly people are being lost along the way. Maybe.

For now, and for whatever it's worth, here is my advice to science journalists that may help improve at least the accuracy of their articles. It could equally be used as advice to readers.
  • Anyone claiming proof is probably lying. If they don't make this claim, don't make it for them. Don't imply a solution with "mystery solved" - no, not even by using "quotation marks". And if they do claim this, then try as hard as you can to get them to admit their level of confidence.
  • Always get a second opinion. Even if the scientists doing the research don't back down, chances are you can find another expert who will most likely not entirely agree with them. If necessary, ask the scientists for people to ask for a more skeptical opinion. It's your job to decide how many levels of counter-responses you want.
  • Ask what it would take to get real proof. There is usually some "wiggle room" for alternative ideas with most theories - try and find out what those are. In some cases proof is impossible.
  • Remember the unknown unknowns. It wouldn't be research if you knew what you were doing (Pratchett, Science of Discworld). Science is hard, and sometimes entirely new ideas or discoveries render previous theories irrelevant. But don't go nuts. There are facts in science, it's not all probabilities. No amount of quackery will ever disprove that the Earth is round.
  • Extraordinary claims require extraordinary evidence, generally speaking. Or rather, be extra vigilant if scientists are claiming a major breakthrough. So NASA are building a warp drive, are they ? Which bit of NASA ? How much thrust is their engine producing ? Has anyone else had a look at it ?
  • Think through the implications of the research. You may find it "odd" that it may be possible to produce meat or cheese without a cow, but potentially that means the elimination of huge herds of methane-producing cattle. "Odd" scarcely does it justice - if it pans out. 
  • Avoid sensationalism. Just because a discovery could one day revolutionise energy production doesn't mean it will, or will anytime soon. Speculation is healthy; implying immediate massive effects makes everyone look pretty stupid.
  • Avoid trivialisation. Chances are that any science story is more important than anything Kim Kardashian will ever or can ever do.
  • Be careful with analogies. They're great for explaining complicated issues, but make it clear that they're only analogies (and if necessary state what their limits are).
  • In short, remember your high school English lessons. Don't sensationalise. Don't trivialise. Be critical, be skeptical, be uncertain, be inquiring, but above all be reasonable. There's no reason - no reason at all - that being moderate has to be boring.

Saturday, 23 May 2015

Substitute Sondy

This was my first outreach-to-camera activity. Fraser Cain said I was a natural. #ChuffedToBits #MassiveEgoBoost ... oh wait, I'm not on twitter, hashtags don't work. No matter. Expect to hear my incredibly annoying voice on future Weekly Space Hangouts when time permits. For now, cringe with horror (horror makes you do that, right ?) as I attempt to explain why radio telescopes are awesome, why dark matter is pretty neat, and why I think we may as well try and talk to aliens for lack of anything better to do.

Oh, and someone asked about the lonely little smurf, which I was totally not expecting. Nice to know that people are paying such close attention. Or maybe it's worrying to know that people are stalking me....

Tuesday, 12 May 2015

Lessons Of The Elections

Substance isn't everything.



Many fellow Labour supporters have bemoaned that Ed Milliband suffered unfairly from a poor public image. Shouldn't it be about substance, not style ? No, it shouldn't - not exclusively. Style matters. A political leader has to be able to inspire people, to not merely motivate but actually make them enthusiastic about things they may have been opposed to - not just to win votes in the first place, but also to maintain support afterwards. That is simply impossible to do with pure rational argument.

I'm a lefty. In fact, I'd have liked even more left-wing policies than Miliband's. But he never inspired me, or persuaded me that he was competent enough to actually make his ideas work, or overcome resistance to them. And if you can't even do that, then no, you're not a good leader. It's a similar problem to Gordon Brown - a tremendously moral man, highly intelligent but a terrible, dreadful manager. He was chronically unable to work well with other people.

Perhaps in a ideal world, everyone would be persuaded entirely by logical argument. But we aren't Vulcans, and failure to acknowledge that is a catastrophic error. Having good ideas is essential, but that doesn't mean anything in a leadership role if you can't persuade people that they're good ideas.


The voting system isn't broken.



Well, not necessarily. The huge disparity between the number of seats won by the Scottish National party (56 - a gain of 50 !) and UKIP (1 - a loss of 1) despite UKIP actually gaining a much higher share of the vote (12% compared to 5%) reveals a very interesting aspect of the first-past-the-post system. Clearly, it is possible for smaller parties to make major breakthroughs. A party which wins a large percentage of the vote but few actual seats is, I submit, not failing because of the system, but failing to understand how to campaign correctly within the system.

Perhaps other voting systems are better or fairer. But the SNP's sweeping victory disproves any idea that a different system is necessary for the success of smaller parties. And, seriously, we recently had a referendum on a different voting system and we rejected it decisively, a fact conveniently forgotten by UKIP. Anyone seeking to change that is going to have a very difficult uphill struggle.

While substance isn't everything, having a single allegedly charismatic leader is only useful if you have other people to back them up - you can't rely exclusively on them to win votes for the other party members.


The voting system is broken.



Or rather, while the system can be fair if you play it correctly, it's not intrinsically a system of proportional representation. It's broken in the sense that currently there are large differences between the share of the vote and the share of the seats that parties win. Even leaving aside the issue of how you play the system, I don't think this is actually such a bad thing. Allow me to explain why I think that if you want to fix the system, you have to be extremely careful about how you do it.

The first-past-the-post system doesn't prevent hung parliaments, but it does make them rare events. It's pretty good at delivering decisive results in favour of one party. Consequently, that's how our politicians campaign and that's how we vote - with the expectation that the party we select will hold office and enact the policies they've put forward. Usually, one party gets a majority and then tries to implement its pledges. Thus, we the people are (in large part) responsible for both choosing the government and its major policies, if not for deciding any specific details.

Where this all goes horribly wrong is when a hung parliament does occur. In that case the system sucks. We don't even get to choose which government is formed (although last time there was really only one practical possibility, a much more even split is possible), let alone which policies we want enacted (this is much worse because the politicians are campaigning in a system where they don't expect to be in a coalition so they don't tell us how flexible they are on most issues). Essentially this gives an unelected government a free hand to choose whatever policies it wants, making the fact that people voted virtually meaningless. No wonder people don't like coalition governments.

The question then becomes : do we want a (more) proportional system of representation, which inevitably means more coalition governments, or do we prefer to occasionally suffer bouts of madness but most of the time get more decisive governments ? While, as I said, political groups do have to work within the established framework of democracy, we also have to recognize that huge numbers of people voted for parties like UKIP which got barely any representation in Parliament at all.

If we do want more proportional representation / coalitions (and I'm not saying I think we do), it's abundantly clear that our voting system is not fit for purpose. We have no way to tell politicians at the ballot box which alliance we prefer, let alone which policies we're voting for. A system where people have a much more direct say in which policies are enacted, rather than which party is elected, might or might not work (that's another issue) but this is simply impossible in the system we have now.

So, to my mind, if you're campaigning for a more proportional system then you should also be campaigning for a better system to ensure that voters get the government and policies that they actually want. Otherwise, we almost lose the "democracy" from "representative democracy" completely - we the people will have little say in which government is formed or what policies it brings forward. Personally I don't want to vote for people simply so they can negotiate policies on my behalf - I want to have a say in how the country is run. Our current system does that since votes for parties and policies are one and the same. By increasing the number of coalition governments, which must necessarily make compromises in ways the voters can't control, proportional representation (without other reforms to the system) could end up making the system more representative but actually less democratic.

In short, voting reform in order to make a fairer system is more complicated than is usually stated. Right now the system is not so broken that this is necessary. Caution is needed.


The left isn't doomed. 


It was an awful election for Labour, but a majority of just five seats hardly makes the Conservative victory any kind of landslide. Labour have recovered from similar defeats before. Moreover, the real disaster area for Labour was not England but Scotland - where they were replaced with a more left-wing party. The political right are currently in the lead, but only just. Left-wing politics is very much alive and well.

Here's the tricky paradox Labour have to very carefully avoid. Scotland voted against austerity and if Labour are to make a comeback there they're going to have to appeal to that ideology. That's widely seen as very left-wing. But simultaneously Labour failed in England by not being pro-middle class enough. Somehow, they need to be more centrist in England and more left in Scotland - or rather, show that anti-austerity measures aren't just about social justice, but fundamentally good for the middle classes. Or, if they don't want to go down the anti-austerity route, then they've got to fight very much harder to convince the Scots that they will make life better for the ordinary voters.

Labour face a major challenge to regain voters at the next election. But, while the SNP are jubilant at the scale of their victory, it should also sound them a note of caution : fortune's wheel is ever turning. Sometimes defeat can be snatched from the jaws of victory.

My own opinion is that to recover from this, Labour needs to get over their moral disappointment in the man who led them to three successive victories, Tony Blair. No, he was not a moral man, but he was a consummate politician. He knew how to win. Better, in my view, to be (seen as) a centre-left winner than a far-left loser.


TV debates aren't all that important, and the parties aren't all the same.



One thing that struck me about the whole campaign was that both sides were struggling to appear as much like their opponents as possible. If you restricted your attention only to the televised "debates", you'd have seen Cameron promoting the most socialist of his welfare policies and Miliband yapping on about the importance of wealth creation. You could easily be forgiven for thinking that both of the main parties are the same.

But the voters weren't fooled. Listening to the questions posed during the debate, it's clear that people had been paying close attention throughout the government's term of office. Cameron was perceived as threatening welfare, Miliband as threatening jobs. Consequently in the debates they both attempted to appear as centrist as possible. Strangely, that Cameron behaved like a child when he consistently refused to turn up for the debates doesn't seem to have done him the slightest damage.

For the second election running, the debates appear to have changed the fortunes of the minor parties not one jot. Last time, the Liberal Democrats saw a huge surge in popularity after their first debate, which completely and utterly failed to translate into winning any votes - indeed they lost seats. This time Clegg cataclysmically failed to undo the damage done by the tuition fee scandal. The Greens, Plaid Cymru, and UKIP all saw no benefit from the debates whatsoever.

Certainly the debates have their place. But it looks to me like it's parliamentary actions over the course of the term that are the real vote-winners. Appearing to be a centre party on a debate isn't enough - if you want to win that coveted centre ground, you have to actually be central. And not go back on your tuition fee promise, of course.


You can't abandon your principles and get away with it.



Some political commentators have said that whenever a smaller political party goes into coalition with a larger one, the result is that it inevitably gets squashed. In this case, I don't agree. I also think Clegg is an idiot if he really believes that losing almost all Liberal Democrat influence was a price worth paying for their being in government, given the appallingly stupid manner in which they shot themselves in the kneecaps. They could still have done pretty much everything they did without committing political suicide.

The Liberal policy of reducing or scrapping tuition fees wasn't just a policy, it was a core principle of the party. It was the reason most people voted for them. The referendum on the alternative vote was important too, but not to anywhere near the extent of tuition fees. Clegg might have been able to get away with not holding the promised referendum if he'd been suitably contrite. Given the choice between an AV referendum (or indeed almost any of the other Liberal policies) and lowering tuition fees, there was really only one option and he took the wrong one.

I liked the Liberals, and I'm disappointed they lost as many seats as they did. But they deserved it. Lowering tuition fees for students may not be the most seriously important moral issue, but going back on that promise was as if Labour decided to privatise the NHS. Politics sometimes necessitates U-turns, especially on flavour-of-the-month policies, but there are limits.

What really was surprising to me was that Clegg stayed as long as he did. I still like Liberal policies, but with Clegg at the helm I simply didn't believe that they meant anything. That total loss of trust made all of their other policies worthless. It was patently obvious to everyone that after that disaster, absolutely no-one else believed Clegg either. If they'd replaced him very soon afterwards, it's possible the blame could have been (correctly) shifted onto him and him alone. As it is, the entire party suffered. Only time will tell if people will believe what the next leader says, or if the damage is more than skin deep.

Thursday, 7 May 2015

The Light Of Other Suns

... because outreach articles should have the most pretentious titles possible, obviously...

There is a justifiably famous video comparing the sizes of various objects in the Universe, most notably, stars. If you have't seen it, I suggest you do so right now. Go ahead. I'll wait.


And that's all well and good, but... just how big are those stars, in real terms ? What would our Solar System look like if we swapped our Sun for Rigel or UY Scuti ?

Long-term readers will remember that I already did this for VY Canis Majoris, then reckoned to be the largest known star.


Since then it's been trumped by the mighty UY Scuti. With this post, I want to do something a little bit different and not just re-render the system with a different star - another wall of fire that's a bit larger than the last one isn't all that interesting. Here I'm going for variety, and animation, because animation is way cooler.

This post is in two parts. First, I'm going to skip ahead to the results because that's what most people are most interested in. The second part looks at how we know these results and some of the pitfalls to be wary of - the short version is that this is only an approximation, but it should be a reasonable one.


1) Lookit all the pretty pictures !

Without further ado, here's the video.


Ah, but maybe you prefer still images ? That's OK, I understand. Here's the first sequence in still form - with extra information added, as a bonus. You lucky people, those chumps who only watched the video don't know what they're missing. We'll get back to the accuracy of this later. Temperatures are in Kelvin; it's easy to convert if you want to. First, the stars smaller than the orbit of Mars (with Jupiter's orbit just visible at the outer edge) :








Note that the parameters don't scale in a nice linear way. A star that's twice the diameter is not necessarily eight times as massive, which is what you'd expect if density remained constant. There are all sorts of reasons for this, not least of which is that the stars themselves are variable, sometimes swelling massively in size and throwing off huge amounts of mass.

Anyway, now we need to zoom out to see the real giants. To properly compare the others, let's start with the Pistol star again.





In the video I show it ending with Voyager 1, which is very much further away again than Pluto (currently 130 AU from the Sun, or 130 times the distance between the Earth and the Sun). If you're wondering, that's only about 0.05% of the distance to the nearest star. So at the speed the camera is moving in the video it would take about 15 hours to reach it.

The advantage of stills is that I can also show you all the views at once. Here's the every star, every planet shot.



Last time, with VY Canis Majoris, people asked about the temperatures of each planet. If that's your thing, have a play with this online calculator. The bottom line is that if you replaced our Sun with a star much smaller or larger than it, we would die. A more interesting exercise for the reader is to calculate the size of the habitable zone for each star.

That about wraps it up for the visuals. If you're really interested in the accuracy, keep reading. If not, here's a short version of some things to bear in mind :
  • Large stars have very low densities, so they won't really have a nice well-defined surface.
  • Measurement errors in the numbers can be considerable, sometimes as much as a factor of a few. Certainly we know that some stars are very much larger than the Sun, but don't go thinking that VY Canis Majoris is exactly 1420 times larger.
  • Stars themselves vary over time ! Most stars go through several distinct phases during their lifetimes, but even within these different stages their size can vary dramatically.
  • I only tried to render the size of the stars accurately in the video/image. Everything else - colours, brightnesses, appearance of the planets - is approximate. These aspects are technically much more difficult to depict accurately than size, and that wasn't the goal of the project.
  • Orbits of the planets are approximated as circles, which is certainly good enough here. To see more accurate depictions, have a look at this.
Finally, this set of imagery is only an attempt to compare different stars, not examine how they change over time. Stellar evolution is another topic entirely. Stars are born, expand, explode or collapse... some of them a bright, some dim, some will live for trillions of years while a few will last less than a million. But that's for another post, sometime. Maybe.


2) How do we know what the stars look like ?

One thing I was particular keen to stress in my original VY Canis Majoris post was that giant stars do not have a well-defined surface. The density is something like a thousand times less than ordinary air (whereas the average density of our Sun is about the same as honey), the gravity in its outer regions less than that of Earth, and the temperature about 3,000 K. Such stars have been described as a "hot vacuum". The extremely low density, high temperature and low gravity mean that they cannot possibly have anything resembling a surface like our own Sun does.

Mmm, that's a seriously hot vacuum alright.
Unfortunately, animating the Solar System with various different stars necessitates a bit of a drop in image quality. Rendering a diffuse object is computationally expensive - about 30 minutes for a single image of VY Canis Majoris. Which means that if I want to animate it, I have to show a surface, because that's much easier to render*. But how does one even define a surface for such a monster, and how is it measured ?

* Unless I want to wait for at least 7 weeks with my computer running at full pelt 24/7. Which I don't.

Well, firstly, it should already be obvious that since stars don't even have a precise surface, depicting one is going to be subject to errors. Lots and lots of errors. This is only ever going to be approximate. The main take-home message - that stars come in very different sizes - is, however, absolutely correct.

You might think that a useful working definition of the star's radius is the point at which it becomes opaque - trouble is, defining "opaque" is tricky. For mathematical reasons, this is usually taken to be the point at which less than 36% of the light passes through unhindered. Exactly how this transmittance varies with radius is complicated and I've no intention of examining this in any detail. This simple definition will have to do.

Anyway, we've got a definition of our "surface", so how do we go about measuring it ? Carefully, that's how. Stars are absolutely tiny compared to the distances between them. Shrink our Sun to the size of an aspirin and Alpha Centauri would be around 300 km away. Even so, it is possible to directly measure the size of a few nearby stars.

Another, cleverer approach is to watch how a star dims when it passes behind the Moon, or how the brightness changes when two stars move past one another in our line of sight. Not easy, but possible.

But the easiest method is to measure the brightness of the star and use a simple relation between brightness per unit area and temperature (which we get from colour) to get the total area and thus convert it into a diameter. Now, this certainly isn't as good as a direct measurement. But deciding what physics to use is like choosing a car : most people would choose the insanely expensive high-performance option if they could, even if they don't actually need it.


Which is fine, I guess, if you're a professional car reviewer or a racing driver or Batman, or something. But if you just need to go to the shops once a week, simpler, cheaper options are available.


The Fiat Panda is no better or worse at getting to the shops and back than a Bugatti Veyron. Similarly, the Stefan-Boltzman law, combined with distance and brightness measurements, allows us to find a good approximation for the stellar diameter. It might not do the job as well as a direct measurement, but it will do. It won't be orders of magnitude wrong, unless we've screwed up the observations somehow. None of our estimates of size will be perfect*, but they will be good enough.

*Another, larger source of error is that some stars vary in size by huge amounts. Betelgeuse, for example, varies in size by as much as a factor of two.

So, we've got our working definition of size and some decent approximations of diameter. OK, we had to compromise on the whole "surface" thing, but now we should try and get the colours and brightnesses as realistic as possible, right ?

Wrong. Sticking with the car analogy, too much realism is like custom-modding a Veyron : very ill-advised. Specifically, it's like adding an extra wheel, filling its tyres with explosives and trying to strap a Shetland pony to the roof - it will make things worse, not better. The result has to be something people are going to want to look at, otherwise everything else is a waste of time.

OK, it's a cow, not a pony. Close enough.
For example, brightness. I've read many sci-fi novels in which the intrepid/hapless explorers find themselves near a red giant star and can see through its outer layers. Perhaps the authors base this on the very low density of giant stars and/or their varying opacity. What they're forgetting is the gargantuan energy output of such beasts. A star which is ten times the mass of the Sun might have a diameter a thousand times that of the Sun but an energy output one hundred thousand times greater*. Which means that the energy output per square metre will be only one-tenth that of the Sun.

* In a few cases, millions. Stars are complicated things.

I say "only" in the sense of "not drastically lower". One-tenth of very very bright is still very very bright. So no, you're not going to be able to see other stars through a red giant. Staring directly at such a star - if you should ever find yourself exploring a distant star system - is a stupid as staring directly at the sun. You is gonna go blind.

Does an object really have colour if it's so bright that you can't look at it... wait, is this some sort of zen ? Can we solve this through meditation and contemplation of the oneness of all things ?

Answer : no.
Anyway, as I said, knowing a star's temperature, it's possible to calculate its "true" colour, or vice-versa. But this is nearly useless since whatever we're supposed to be using to view this blindingly-powerful star will need some kind of filter, which will also change the perceived colour. And then there are temperature variations which will cause strong deviations from the average, which makes calculating the predicted colour very much harder. Never mind that stars don't -  in practise - follow the predicted temperature-colour correlation all that well, or that technically it is not at all straightforward to convert a star's brightness into a format the 3D modelling software can understand, or that getting a camera setting where both planetary and stellar surface features are visible* is not at all simple.

* CGI buffs will notice that I put a little backlighting on the planets, which is not realistic in space. However I wanted the audience to be able to see clear differences in the planets and not just slightly different silhouettes, and this seemed like a good approach.

Basically, there are two solutions : 1) Spend weeks, if not months or years, doing a proper analysis of stellar atmospheres; 2) Make it up.

I went for option 2. It's enough to know that cooler stars look red and hotter stars look blue. Even the most expert viewers will have a tough time saying whether each star has the correct colour, because of the arbitrary, unknown filter choice of the visualisation. So there's really just no point at all in option 1, or even calculating the average colours in a simple way based on temperature. What I've gone for, then, is something which depicts the size of the stars as accurately as is possible, but rendered in such a way as to look engaging for the viewer.

Finally, obtaining the figures. This was done by searching a variety of sources, usually starting with Wikipedia. Estimates in some cases (especially for luminosities and masses) varied considerably for each star, so for these I chose the most common value. Where available figures were limited, I opted for reputable astronomy sites (especially Universe Today and Bad Astronomy) over Wiki every time.