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



Thursday, 28 March 2013

Binge Drinking vs Binge Coding

Binge drinking is a bit like wrestling a shark, it might be fun, but it's not necessarily a good idea to video your activities and post them on YouTube. Seriously, read the links.



Binge coding - that is, doing nothing but writing computer code day in, day out - can also have deleterious effects. Currently, moments after waking (usually around 6:30, which doesn't help) and overcoming the customary momentary existential crisis - a sort of mental flailing of the arms - the first thing I find myself thinking is something like, "Hmm, I wonder how I can translate the bounding box values in a postscript file into the world coordinate system of an HI data cube ?"

And yes, you're right, that is a little worrying.

I continue to be unwaveringly preoccupied with such esotericisms (no, spellchecker, I did not mean eroticisms) until very late at night. At which point, while shaking slightly and murmuring things like, "renzograms...  matplotlib...  mesh geometry all wrong..." I reluctantly surrender consciousness. And that's on a Saturday.

Alright, I'll confess. My ulterior motive for this post is that I'm really hoping to generate a Googlewhack*. It turns out that there are currently zero results returned in Google for "renzogram matplotlib." Matplotlib is a popular graph-plotting package for Python. Renzograms are a curiously unpopular (though hardly unknown) type of plot, of which more in a subsequent post, perhaps (they can be really quite pretty, especially in 3D).

* With luck, this will be the least viewed post ever !

They also look quite a lot like the time vortex in Dr Who. This may well be the first ever renzogram generated by matplotlib posted on the internet. GO ME !

Anyway, the effects of binge drinking and binge coding can be very similar. For one thing, both cause anti-social behaviour, though of radically different natures. An angry drunk may tend to hit people. A happy drunk may tend to hit on people, or possibly just sing loud obnoxious songs. Whereas the binge coder will simply refuse natural light, shun all human contact and occasionally wonder why no-one's calling any more.


The effects are also similarly dissimilar on health. In the short term, neither does very much harm except to cause an unpleasant sense of confusion and a headache. In the longer term, full-blown alcoholism leads to all kinds of problems, like death. I can't imagine that it's physically possible to code oneself to death -

if self.alive == true:
   reality.unlink(self)

- probably doesn't work, for instance, but it's certainly not going to convey much in the way of health benefits to be shut away in a darkened room gorging on all manner of snack food with nothing to drink except tea and root beer. Well.... not if this continues for a whole year, at any rate.

However, binge drinking can be (except in extreme cases) self-limiting. Eventually, you run out of money, or throw up, or pass out, or possibly all three (but not necessarily in that order). Unfortunately, there's no such in-built safety net with binge coding, In fact, binge coding will more often than not leave you with more money that when you started.

Case in point.

Granted (to pick an example ENTIRELY AT RANDOM) generating, oh, I don't know, renzograms with matplotlib is unlikely to lead to the next Angry Birds, but it's still earning a salary rather than burning one. While I suppose sheer exhaustion might cause you to pass out eventually, it's probably not possible to code oneself into puking :

if self.coding >= excessive:
   for x in self.stomach:
      remove.x

No, the only way to beat binge coding is to see it through to the bitter end. To fix ALL of the bugs so that generating renzograms with matplotlib becomes foolproof. And then eventually you find that all is done and you can resume science and write more coherent blog posts.

Tuesday, 26 March 2013

SPIKE

Thanks, reddit ! You rock !
Welcome, new followers ! May your visit be educational and your hovercraft full of eels !

Wait, what ? NEW followers ? NEW followers ??? Oh crap oh crap oh crap oh crap oh crap.... this means I have to make more content.... umm.... wasn't really prepared for this... bugger. Err, in the meantime, here are some popular articles you might enjoy, or might enjoy posting on reddit, or might not.



Deep Space Force
Galaxies are Pretty
Beginner's Guide to the Universe

Excuse me while I scramble to find something else to write about.... err.... back in a bit !

Monday, 25 March 2013

VY Canis Majoris - Or, Be Afraid. Be Very Afraid.

Recently I came across the following image :


Supposedly it depicts VY Canis Majoris, the largest known star. Not the most massive or the brightest, but the one with the largest diameter - a truly terrifying 1420 times bigger than our own Sun. It's a beautiful and inspirational image by the talented artist Facundo Diaz. But is it accurate ?

The image grabbed my attention, but the properly-cited physical characteristics on Wikipedia are what's really stunning. Other images have tried to put into perspective just how frickin' gargantuan this behemoth is, but I want to tackle this in a slightly different way. The most natural approach to me is to consider what would happen if, somehow, our Sun was magically and instantaneous swapped with VY Canis Majoris.

The result, in a word, is death. Complete and total death. Mercury, Venus, Earth, Mars, the million tiny worlds of the main asteroid belt, and even Jupiter - all gone. Jupiter, in fact, would find itself about 70 million miles below the surface of the star. It's a thought experiment to make Schrodinger's Cat look like the kindest act of animal welfare.



"Surface" in this case is a tricky concept. Although the star is staggeringly vast, it doesn't have all that much mass, considering. It may have a volume 10 billion times greater than the Sun, but its mass is only 17 times greater. That gives it an average density of next to nothing - a thousand times thinner than ordinary air (of course, the interior regions where nuclear fusion is occurring will be very much denser).

Not only is the outer part of the star a pretty good approximation to a vacuum, but the gravity would also be only about a quarter as much as on the surface of the Earth (on the surface of our own Sun, gravity is about 28 times higher than on Earth). And that means that the nice, well-defined spheres in the above images are just wrong. It might be better to think of it as a searingly hot, blinding nebula than a star. It might not even be spherical.

What it definitely would be is utterly spectacular. From the orbit of Saturn, the star would fill half the sky. It would appear less like a star and more like a stupendous flaming wall of fire.

I cannot hope to match the beauty of Diaz's render, but I shall give it a damn good try.

Actually, what it would look like to the naked eye is not much of anything, because it would cause instant blindness. The surface brightness of the star (i.e. how much energy it's putting out per square meter) is about one-sixth that of the Sun, which for all intents and purposes makes no difference. Imagine the Sun filling half the sky, and you get the idea.

In fact it's somewhat worse that that, because the amount of energy received by a luckless "observer" would be about five million Watts per square meter at Saturn - roughly 5,000 times what you get from the Sun on Earth. So there'd be no need to worry about the blindness because there wouldn't be time. The rings of Saturn - if not actually the planet itself - wouldn't last long either.

This means that whether Diaz's wonderful image is accurate or not is a moot point. It would be a sight, quite literally, of such awesome power that no human eye could ever see it.

Moving further out, things get better - slowly - but only because they can't very well get any worse. At the orbit of Uranus, the Star (it deserves a capital letter, and a better name) still absolutely dominates the view.



If we move along a planet, we come to Neptune. Now we can start to see that the Star is embedded in a nebula. This isn't surprising, given the insane amount of energy output, the low surface gravity and density - effectively, it's evaporating, wrapping itself in its own death shroud, if you will.

I cheated a little bit here. The "nebula" is actually an image of the Large Magellanic Cloud - a nearby galaxy - as seen in the infra-red.

At Pluto, the Star still appears much larger in view than the Sun does from Earth. Just in case I haven't hammered the point home yet, it's absolutely ginagorous.



The most distant man-made object is currently the Voyager 1 spacecraft. One hundred and twenty times further away from the Sun than Earth, it's somewhere that can only be described as cold, dark and incredibly lonely. Not so if our puny Sun makes way for YV Canis Majoris. Astonishingly, at this huge distance it would still span 6 degrees. The Sun as seen from Earth spans only 0.5 degrees.

Voyager model from NASA.

Oh, and I almost forgot. One day, this star is going to explode. Isn't science fun ?

Monday, 18 March 2013

Why I'm Not On Twitter And Never Will Be

I don't use Twitter. But if I did, I imagine my posts would go something like this :


I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I FOUND SOME HYDROGEN !

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I FOUND SOME HYDROGEN !

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I FOUND SOME HYDROGEN !

I am looking for hydrogen.

I am looking for hydrogen.

I FOUND SOME HYDROGEN !

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I FOUND SOME HYDROGEN !

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I FOUND SOME HYDROGEN !

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I FOUND SOME HYDROGEN !

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I FOUND SOME HYDROGEN !

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I FOUND SOME HYDROGEN !

I am looking for hydrogen.

I am looking for hydrogen.

I FOUND SOME HYDROGEN !

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I FOUND SOME HYDROGEN !

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I FOUND SOME HYDROGEN !

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I am looking for hydrogen.

I HAS FOUND ALL OF THE HYDROGEN. I HAS THE WIN.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I am downloading FITS files.

I have downloaded ALL of the FITS files. I R A WINNER !

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

I am doing photometry.

PHOTOMETRY IS DONE ! IT IS DA SHIZZLE.

I am looking for trends in data.

I am looking for trends in data.

I am looking for trends in data.

I am looking for trends in data.

I am looking for trends in data.

I am looking for trends in data.

I am looking for trends in data.

I am looking for trends in data.

I am looking for trends in data.

I am looking for trends in data.

Bored now. Writing code.

Codin'.

Still codin'.

Code is done. Took 3 days. Has just made last 6 months of work obsolete.

Sigh....

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

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I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

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I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

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I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

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I am writing a paper.

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I am writing a paper.

I am writing a paper.

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I am writing a paper.

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I am writing a paper.

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I am writing a paper.

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I am writing a paper.

I am writing a paper.

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I am writing a paper.

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I am writing a paper.

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I am writing a paper.

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I am writing a paper.

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I am writing a paper.

I am writing a paper.

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I am writing a paper.

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I am writing a paper.

I am writing a paper.

I am writing a paper.

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I am writing a paper.

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I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

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I am writing a paper.

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I am writing a paper.

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I am writing a paper.

I am writing a paper.

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I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

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I am writing a paper.

I am writing a paper.

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I am writing a paper.

I am writing a paper.

I am writing a paper.

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I am writing a paper.

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I am writing a paper.

I am writing a paper.

I am writing a paper.

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I am writing a paper.

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I am writing a paper.

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I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I am writing a paper.

I HAS SUBMITTED A PAPER. NOW I SLEEP.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

I am revising a paper.

PAPER IS ACCEPTED ! MWHAHAHAHAH !

I am looking for hydrogen.

Wednesday, 13 March 2013

Galaxies Are Pretty

EDIT : This is an old post from 2013, updated as of March 2016 to include new data.

I've always wanted to understand how the Universe works. This is proving rather difficult, so I'm prepared to settle for knowing what it looks like.


Since I already describe the technical aspects of how the video was produced on my website and in an earlier blog post, I'm not going to do it again because that would be silly. EDIT : I will just add a brief note - you might notice in the video that there's a difference in the number of galaxies detected by ALFALFA and actually shown here. That's because some of them aren't galaxies at all, and a few aren't properly identified by the SDSS automatic algorithms.

 Maybe a more interesting question to ask is : how accurate is the video ? Is this really what the Universe looks like ?

Well, no, it isn't. It's an approximation, but it's grounded in reality. Allow me to try and explain, because it's my blog and you can't stop me.


The complete, full HD video. Partially in 3D if you've got those 
old red-blue glasses. The original can be seen here.


How do we know where all the galaxies are ?

We don't. Just looking at an image isn't always enough to tell what's a galaxy and what isn't. For example... THIS


isn't a galaxy. It's just a crummy old star cluster, and therefore useless. Whereas THIS


is a genuine galaxy and no mistake.

Just like with James Spader and Michael Shanks, there's no way to tell the two apart by just ogling them. But if we measure how fast their stars are moving, we can see that all is well with the star cluster, but the stars in the galaxy are moving way too fast. Without some invisible matter to hold them all together, they should all fly apart (unless we've got something very wrong, which is possible, but in the interests of time let's not go there). So galaxies have dark matter, and star clusters don't.

Whereas distinguishing Spader / Shanks is simply hopeless.
Unfortunately we can't always get accurate measurements of how fast the galaxies are rotating. Sometimes, though, we can measure how far away they are, and that tells us if we're looking at a small bunch of stars very nearby (which would be a star cluster) or a big bunch of stars very far away (which would be a galaxy). More on that in a minute.

Still, the upshot is that identifying galaxies is tricky, and we can't be sure we've found them all. In fact, we know we haven't, because the Milky Way is big, bright, and in the way.

And very pretty.
More important is that the galaxies in the video are selected from the ALFALFA survey. This is a hydrogen gas survey, and galaxies which have hydrogen tend to be forming lots of stars and very blue. So the video is missing a lot of the reddest galaxies, even the really bright ones, because these often lack hydrogen gas. This was a deliberate choice, because I made the video to demonstrate the capabilities of Arecibo in a photogenic way, and neither Michael Shanks nor James Spader seemed to fit the bill.


How do we know how far away the galaxies are ?

We may not know exactly where all the galaxies are, but for those we do know about we generally have pretty good estimates of how far away they are - even though we can't directly measure the distances to other galaxies.

The only way we can directly measure the distances to astronomical objects outside of our own solar system is through parallax, where we see how much a star moves relative to the stars behind it. That's good for nearby stars, but for more distant objects we have to use other methods (calibrated on the ones we can get direct measurements for) to create a 'distance ladder'. And that lets us get pretty good estimates of how far away galaxies are.

Full size image here.
The most important result of this is Hubble's Law. This allows us to use measurements of how fast the galaxies are moving away from us (a relatively easy measurement) and convert it into a distance. And we think this works pretty well... most of the time. The problems start when you get two or more galaxies close together. Like two sumo wrestlers on a trampoline, the force of attraction is irresistible*  and they can't help but fall towards each other. And that screws up the conversion of velocity to distance.


* It's not really irresistible - it's relatively rare for galaxies to collide and merge**, but they do affect each other's velocity.
** Merging is even rarer - and considerably more unpleasant - for sumo wrestlers.

This is particularly bad in galaxy clusters, which are the equivalent not of sumo wrestlers, but a bunch of obese, angry rabid cats on a trampoline, possibly on fire - the Platonic ideal of chaos. Here, the velocity measurements tell us practically nothing about distance. Some galaxies are even coming toward us, which would give a meaningless, negative distance if we were silly enough to take Hubble's Law at face value. So the galaxy distances in the GIF are pretty good, but far from perfect. There's just no way around that, because better data doesn't exist.


Do the galaxies really look like that ?

No they don't. The images used are optical images from the Sloan Digital Sky Survey, but just because they were observed at similar wavelengths that we use to see with doesn't mean they look like what you'd see with your naked eye.

For starters, they're all much too bright. Think about what the Milky Way looks like on a clear, dark night. Does it really look like this ?


Hell no. The real thing looks beautiful, but nowhere near as bright or as colourful - not even in the darkest spot on the darkest night. Images like this are only possible with long exposures, or large telescopes. So out of necessity - because the video would show bugger all otherwise - the galaxies are shown much brighter than you'd really see them.

The colours aren't 'true' either. but that shouldn't bother you. Everyone perceives colour in a slightly different way - it's practically a subjective choice, rather than a measurement. And then, of course, some people are colourblind. The important point is that the colours are relatively correct - things which look bluer really are bluer than things which are redder.


EDIT : Since making the original, the Sloan Digital Sky Survey (which is where the galaxy images come from) updated their data processing techniques. The results make the galaxies look rather redder and blue features almost disappear - especially given the particular technique I'm using to display them in Blender. Fortunately, a bit of simple colour correction restored the galaxies to their former glory.

Left to right : 1) Raw image from the SDSS; 2) Galaxy as displayed in Blender without colour correction; 3) Galaxy displayed in Blender with colour correction.
This makes a very dramatic difference indeed for the whole set of galaxies. Here's what they would look like if I hadn't done the correction :


Flat, dull yellow. Drab, even. In the words of Bart Simpson, "Wow, the Universe is so boring !". Fortunately, that bit of colour adjustment brings out all the shiny details and stops it from looking a particularly unpleasant shade of beige.

A Universe rich in stars, galaxies, flying spaghetti monsters, etc.

What about the sizes of the galaxies ? Like brightness, these are exaggerated out of necessity, by about a factor of 40. That means that you can see the structures in many galaxies at once, without hoping that the viewpoint passes very close to them (otherwise you'd just see a bunch of small, uninteresting fuzzy blobs). However, as with colour, the relative differences are correct : a galaxy that looks twice as big as another really is twice its size.

One thing there was no need to compromise was the structures visible in the galaxies. Each of the 23,935 galaxies in the video is represented by an optical image of the actual galaxy seen at its location. This is pretty unusual - many of these large-scale videos often just use a few hundred template images. Here, there are unique images of every single blasted one. Don't believe me ? Here's the complete sample.

EDIT : This is from the original version of the post, which used a mere 11,710 galaxies. I can't be bothered to remake this.

View this in full, terrifying detail here.
Astute viewers may note that some of the images look strange. Unfortunately, there aren't any good estimates available for how wide the galaxies are. A large survey like this has most of the data processed automatically, and inevitably sometimes something goes wrong - especially on the large galaxies, which are often (incorrectly) broken up in the catalogue into several pieces.

I had a choice here. The first option was to carefully check all 11,710 23,935 images and make sure the galaxies were the correct size. This option was stupid, so I chose the second option, which was to ignore the problem completely.

Finally, we'll never know exactly what some galaxies really look like, because we're seeing them from a jaunty angle. We can correct for this to some extent, but only if we know the minimum and maximum dimensions of the galaxy. Which, for this sample, we don't. And if a galaxy is edge-on to us, there's nothing at all we can do except go home and cry.


In summary then, the video shows what you'd see if you had super-sensitive eyes and all the galaxies were forty times bigger than they actually are, with lots of errors. The large-scale structures of filaments and voids you see are correct, but not complete. That's a correctable problem, and one I might tackle at some point. But since downloading 11,000 images took about 8 hours, it can wait.

Tuesday, 5 March 2013

Surfing the Fiscal Glacier

For those who have been living in a swamp but have just returned to civilization desperate to catch up with Physicists of the Caribbean (there must be thousands in that situation, right ?) - the US government decided some time ago to agree to disagree. No-one could work out how to do spend all the money, so they more or less opted to just carry on as normal and try and work things out later - a multi-billion dollar, "meeeehhh", if you will.



This might, perhaps, have been a workable plan if the disagreements had been about whether the Capitol building needed an extra water cooler or not. Alas this was not the case. Firstly, for reasons that entirely escape me, the US is going for austerity measures even in a time when its economy is growing. That seems to me a good definition of shooting oneself in the foot, but since I admit to having all the financial acumen of a piece of runny cheese, I'll let it slide.

"Quick, burn it before the poor people can get it any !"
More importantly, while British politics suffers from being really quite breathtakingly dull*, American politics has the opposite problem. In Britain, the two sides will make token attacks on each other's policies, full of sound and fury but signifying nothing. Since these are often the policies they themselves were once calling for, this is rarely convincing. Differences between the parties have become almost Lilliputian.

* But see my earlier, somewhat desperate attempt to liven things up.

Not so in American politics. Here, it seems that everyone hates the other's guts and actively wants them choke to death on a live poisonous snake, or something. At least, that's the impression I get. It's as though every party member really believes that the other side broke their house and burnt their legs down, then raped their pets and murdered their family. Or something very similar.

Actually, this is much as the great Welsh politican Nye Bevan felt about the Tory party 50 years ago. The situation is probably worse here though, because the electorate are split almost exactly 50-50. On the one hand we have the Democrats, a fairly right-wing party by European standards, and on the other, the Republicans. These latter, as far as I can tell, are not so much a political party as they are pantomime villain rejects.


(that said, the Republicans may all be stark raving mad. but if you want to find some seriously messed-up politicians, look to India)

However, the these two groups of mortal enemies, who often seemed quite willing to physically throttle each other, decided that there was a way to reconcile their differences, for the good of the country. And that way was, metaphorically speaking, to lock themselves in an empty room with limited oxygen from which they could only escape by behaving equitably towards each other for several days. And remember, half of this group are bona fide insane.


The non-metaphorical, self-inflicted punishment was to be the fiscal cliff. This was a wonderful, all-inclusive, $85 billion dollar package of cuts to the economy that would hit automatically at some point if an agreement could not be reached. Absolutely no-one wanted this to happen - even the Republicans, who seem think that America deserves as many horses and bayonets as money can buy.

Well, surprise surprise, these two diametrically opposed forces just couldn't reconcile their differences, my goodness me, whoever could have foreseen this ? Still, they weren't about to risk messing with the economy, so with a mighty collective effort they decided to kick the can down the road a bit more. Thus, this is a slowly-advancing cliff : to wit, a glacier.

But not nearly as pretty, or as useful.
Unfortunately on the second or third attempt both sides called the other's bluff. Or to extend the metaphor, they both played chicken with a glacier and lost. This is a singular accomplishment, and really should win them both an IgNobel for economics, although possibly the economic equivalent of a Darwin Award might be better.

The fiscal glacier, then, has calved. For science this is particularly nasty, with the great hunk of icy funding that's crashed into the sea constituting about 8% of the mass of the whole frozen river (that link is worth clicking). So what happens next ? Do we sink, swim, or surf the impact wave to freedom ?

Look closely, and you'll realise how awesome this is.

My guess is none of the above. We'll probably tread water until we all die of hypothermia. Yay.