Social and anti-social astronomers

June 7, 2011

Its exam time. Don’t we love it. Students and Staff alike. We do ours a little earlier than most, so my marking is all done and we are in the middle of exam boards. Its a multi-stage process these days, with separate special circumstances committees, pre-boards, and stage-1 course boards, before the official final exam board. The latter then largely homologates the recommendations of these earlier committees. Probably more efficient than it used to be, but even more bureaucratic. So we all look forward to the small amount of socialisation that goes with the process – the annual exam board dinner !

So there we were last night, at Blonde. By the way, I recommend you don’t Google “Blonde, Edinburgh” unless you have safe search switched on. Or on the other hand… anyway. It was a fairly usual mix. Gossiping about George and Carlos and the Gruber Prize, bitching about absent members of staff, and as the wine flowed on, bitching about present members of staff. But there was also an interesting conversation about Blogs and Twitter.

Nearly everybody present was a Luddite and thought blogs and tweeting were onanistic and time wasting. A polite exception was made for my blog, and Peter’s, on account of they were (at least sometimes) a useful community conversation forum. Myself and @wikimir and @paula_wilkie were the only Tweeters. To everybody else, Twitter seemed even more clearly bizarrely pointless. People thought the idea of @WETI was funny, but that was seen as a joke on Tweeting. I was challenged to describe a real use of Twitter. About the best I could come up with was that Paul Crowther knew everything first, and that if you followed him on Twitter, you would know everything second. The response to this was “whats the hurry ?”

Then this morning I became aware of an interesting new attempt to make Twitter useful – the Astronomy Journal Club, set up by Emma Rigby, Matt Burleigh, and Emily Baldwin. I learned about it first in Sarah Kendrew’s blog post here. Its all brand new, so who knows if its going to work, but why not give it a go ?


A dim glimmer

March 3, 2011

As I write this, I am sitting in Sheffield’s fine Victorian railway station, on my way home from visiting the astronomers here. Yesterday I sang for my supper, giving a double bill seminar on the radio background and on the big blue bump. Supper duly followed, and was exceeding pleasant. The Sheffield group is a small but lively one. As normal, the postdocs were worried about job prospects and the academics were moaning about writing exam questions. To quote P.C. : “I love my job but I hate writing exam questions.” With you there, Professor C.

The Crowther mentioned my recent blog post about how the Universe is almost empty. He said he likes to set his classes ballpark estimate exercises. He tried one out on me. You can have a go too. Its quite good to start by using your instinct to make a guess, before gathering a few facts to do the quick mental calculation. That way you can get your frisson of surprise. Suppose, said Paul, you take the material of the Earth and stretch it out from here to the Sun – how wide would that rope be ? His students guess a wide range of answers, but usually around a mm. Give it a go.

Here is another one, for which I will give you the answer – how powerful is a one kg accreting black hole ? As we all know, quasars are immensely luminous because they have supermassive black holes at their hearts – those accreting black holes are the most efficient energy sources we know. We are talking big numbers. At the Eddington limit, that billion solar mass black hole can be radiating up to 10^47 erg/s. When I first came to giving an undergraduate course with some of this stuff in, I felt duty bound to do things in SI units. So I got a formula for the Eddington limit : L_Edd=6.37M. Wuh ? A one kg black hole gives me 6 Watts ? My electric fire can do better than that ! My electric fire is only a few kg,  but it gives me 2 kW.

Then comes the epiphany. You realise that accretion is not the slightest bit efficient per unit of mass of accretor ; what is impressive is the energy per unit mass of the accretee. To get 2kW out and so heat your bedsit, you need a black hole of at least 314 kg – about as big as two motorbikes. However, once you have it, the rate you have to burn fuel as it were, i.e. the rate at which you need to drop matter into the black hole, is about 2 x 10^-13 kg/s; one kg of fuel would last you roughly 140,000 years… I now leave it as an exercise for the reader how long a kg of coal would give that same 2kW. Scaling up to the most luminous quasars, you need to eat about 20 solar masses a year. Peanuts.

Then it made me think again about that electric bar fire. Its not really producing 2kW all by itself. It is plugged in and sucking that energy out of a giant power station miles away. Its really a similar story. First you need a vast power factory, and all the surrounding infrastructure. Only once you have it can you burn some fuel and give the illusion of that tiny fire producing energy. Likewise, before you can get that accretion energy goodness, you somehow have to assemble those billion solar masses. But thats another story…


Cosmology/Glasgow exam technique

April 15, 2010

Along with a large fraction of the UK astronomical community, I am at the National Astronomy Meeting (NAM2010) in Glasgow. Just imagine a well placed bomb. Could be like the Manchester United Plane Crash all over again.

Two fabulous plenary talks this morning from George Esthathiou and Rosie Wyse. Plack has completed its first survey, but George is not allowed to show us the CMB maps yet. We have to wait until October 2012. (Southwood was in the audience, so he had to behave…) But he did give us a taster – Galactic cold dust map, made by combining Planck and IRAS.  Rosie Wyse showed us all sorts of fascinating stellar population data reflecting the merger history of the Milky Way and other nearby galaxies, as expected in the standard CDM cosmology. But she also showed two worrying things. The thick disc is thought to be made by mergers stirring up an older thin disc. But the stars in the thick disc are really old, suggesting the thick disc of the Milky Way has not been affected by mergers since about redshift two. The second niggle was that the distribution of abundances is consistent with the stellar initial mass function being constant through cosmic history – whereas the galaxy formation simulators desperately want early star formation to be high-mass biased. Hmmm.

Brain spinning, I wandered across the corridor to the Hunterian Museum. This has one of my favourite pieces of Glasgow History – the Blackstone Chair. From mediaeval times until the 19th century, this is how Glasgow students were examined. When you were ready, you sat on a special chair surrounded by Profs. They fired questions at you for twenty minutes, with the sand running out just behind your head. Then some flunky stamped a pole on the ground and you were done.

We gotta bring this back.


Exams, browsers, and the Outernet

March 12, 2010

Going slightly stir crazy, trying to write exam questions. I can never understand why it’s so hard … it ought to be easy, but it ain’t. There is a real motivational barrier. Every so often yer hasster take a break.

So what does an astrogeek do for relaxation ? Why, of course, roam the Internut and find free software to try out. Recently I have been systematically test driving web browsers. At the end of the day, I stick with Firefox because its the only thing that works with Zotero and (reliably) with Tiddlywiki, both of which I use every day, but I have checked out Safari, SeamonkeyCamino, Chrome, Opera, Flock, and Konqueror (on my Ubuntu VM). They are all pretty much of a muchness. Flock is trendy and slightly different because it has built in social networking stuff, but hey, I will leave that to the kids, like Eric. Amaya is also somewhat different – its a web authoring tool, but you can use it as a browser.

But at last I found something different, and fun : Outernet Explorer. This is a web browser written by an artist called Gregor Wright. No need to think. Just press Go. The app generates a random search phrase, bungs it into Bing, and you get what you get. Surprises await. Hours of random fun. Love it.

Possibly even better is the Dream Generator. Last night you dreamed that … you were vomiting on an ambulance in a zoo. Last night you dreamed that … a drunk architect was biting you. Last night you dreamed that … a zebra was running away from you in an empty warehouse. Last night you dreamed that … a gang of angry astronomers evaporated.

Nearly as good as Weirdsville. Regular readers may also remember Tom Collins’ stochastic music website, which Steve Serjeant put us on to. Further aleatoric contributions welcome, short of whole novels. I did try to read The Naked Lunch, but I think I concluded random is best in short bursts.


Astro Bloopers

May 28, 2007

Ah, ’tis May time and exams are here ! I hear the distant scratching of a thousand pens in echoing sports halls and I know that all is right with the academic world. The future hangs in the balance; careers are won and lost; the glittering prizes brighten and fade, as inspiration approaches and recedes. But, thanks to Statistics, there are certainties in this contingent world. We just know that most students will do kinda ok; a handful will stun us; and a handful will turn in utter gibberish. Here are some of my favourites, collected from a few years worth of astronomy exams.

Most are from first year Astronomy courses for a wide range of students – what I believe our American chums call “Astronomy for Poets” or “Scopes for Dopes”. But some are from junior and senior honours students .. see if you can tell which..

All real folks.


  • Doppler shift is an effect which doesn’t take place on the poles of the earth, but it does everywhere else.
  • Black bodies do not emit any light, as they are a box with a tiny hole in. Light enters the hole, bounces around the box, and cannot get out again.
  • IR observations tend to be used for trying to find new plants, which at 300K fit neatly in the IR spectrum.
  • Physics is terrestrial whereas astronomy is conducted on an astral plane.
  • IR astronomy is carried out with an instrument called a bola meter, which is made of geranium.
  • Interferometry works because when the dishes are a certain distance apart the radio waves are syncopated.
  • We know there is dark matter in galaxies as they rotate faster than they ought to, so dark matter must be absorbing some of the light…
  • X-ray astronomy must be carried out from space otherwise the radiation would have a damaging effect on Earth, causing cancer and so on.
  • For spiral galaxies, the linewidth technique is known as Tully-Fisher, whereas for elliptical galaxies it is the Fabry Perot method.
  • part of answer to “describe the universe as seen at different wavelengths”….. The infrared universe is a great deal more colourful, although the colour is often false and generated by a computer.
  • Black-body radiation requires dark matter.
  • The spectral shape of the radiation from black-bodies is determined by the allocation of nearby bodies, as the gravitational attraction from these can “stretch” the radiation and make it more elliptical.
  • The rotation curves of galaxies are the wrong shape. This is because dark matter is concentrated towards the centre, absorbing the light and preventing us from obtaining accurate velocities for this part of the galaxy.
  • Astronomy can be seen as applied physics, and indeed most great astronomers have also been great physicians.
  • In astronomy, all experiments conducted are out of our control.
  • We now know of two black holes, Cygnus I and the one at the centre of the Kerr galaxy.
  • A dynamically relaxed system obeys the viral theorem.
  • If it weren’t for Physics, Astronomy would only be the observation of the pretty bright specs we can see in the sky.
  • Answer to “how would Earth’s orbital velocity change if sixteen times closer to the Sun ?”… If the Earth were sixteen times closer to the Sun, it would vaporise and so its orbital velocity would be zero.
  • X-rays from around black holes are produced by accension belts.
  • The radio emission from quasars is not blackbody emission because that is a theoretical concept and does not actually exist in the universe.
  • White dwarfs are white because they are mostly made of carbon and oxygen i.e. CO, which is a white solid.
  • There is no spheroidal component in the Milky Way, as at night we can see that all the stars are in a thin line.
  • When forced closer together, the electrons buss about more violently.
  • A Type II supernova is the death of a star resulting in a big explosion. This only happens once per star.
  • A pulsar is a neutron star that emits ultra-violent radiation.
  • The Sun is a main sequence star. This is the most common type of star in the solar system.
  • The denser the body the less radiation they emit. The most extreme case being “black body” radiation where no detectable radiation is emitted.
  • The mass of the solar system is 10**12 solar masses. When divided by all the stars we estimate, that comes out at 30 solar masses per star.
  • We calculate the distance to the Sun by bouncing radar signals off Venice at six monthly intervals.