I’m currently in transit to a conference in Ascona (Switzerland) so I thought I’d leave you for a while with something from the wacky and whimsical, weird and wonderful world of Ivor Cutler:
Archive for July, 2009
A chance encounter with the parent of a prospective student the other day led eventually to the question What’s the difference between Astronomy and Astrophysics? This is something I’m asked quite often so I thought I’d comment on here for those who might stumble across it. I teach a first-year course module entitled “Astrophysical Concepts”. One of the things I try to do in the first lecture is explain that difference. The Oxford English Dictionary gives the following primary definition for astronomy:
The science which treats of the constitution, relative positions, and motions of the heavenly bodies; that is, of all the bodies in the material universe outside of the earth, as well as of the earth itself in its relations to them.
Astrophysics, on the other hand, is described as
That branch of astronomy which treats of the physical or chemical properties of the celestial bodies.
So astrophysics is regarded as a subset of astronomy which is primarily concerned with understanding the properties of stars and galaxies, rather than just measuring their positions and motions. It is possible to assign a fairly precise date when astrophysics first came into use in English because, at least in the early years of the subject, it was almost exclusively associated with astronomical spectroscopy. Indeed the OED gives the following text as the first occurence of astrophysics, in 1869:
As a subject for the investigations of the astro-physicist, the examination of the luminous spectras of the heavenly bodies has proved a remarkably fruitful one
The scientific analysis of astronomical spectra began with a paper William Hyde Wollaston in the Philosophical Transactions of the Royal Society Vol. 102, p. 378, 1802. He was the first person to notice the presence of dark bands in the optical spectrum of the Sun. These bands were subsequently analysed in great detail by Joseph von Fraunhofer in a paper published in 1814 and are now usually known as Fraunhofer lines. Technical difficulties made it impossible to obtain spectra of stars other than the Sun for a considerable time, but William Huggins finally succeeded in 1864. A drawing of his pioneering spectroscope is shown below.
Meanwhile, fundamental work by Gustav Kirchoff and Robert Bunsen had been helping to establish an understanding the spectra produced by hot gases. The identification of features in the Sun’s spectrum with similar lines produced in laboratory experiments led to a breakthrough in our understanding of the Universe whose importance shouldn’t be underestimated. The Sun and stars were inaccessible to direct experimental test during the 19th Century (as they are now). But spectroscopy now made it possible to gather evidence about their chemical composition as well as physical properties. Most importantly, spectroscopy provided definitive evidence that the Sun wasn’t made of some kind of exotic unknowable celestial material, but of the same kind of stuff (mainly Hydrogen) that could be studied on Earth. This realization opened the possibility of applying the physical understanding gained from small-scale experiments to the largest scale phenomena that could be seen. The science of astrophysics was born. One of the leading journals in which professional astronomers and astrophysicists publish their research is called the Astrophysical Journal, which was founded in 1895 and is still going strong. The central importance of the (still) young field of spectroscopy can be appreciated from the subtitle given to the journal: Initially the branch of physics most important to astrophysics was atomic physics since the lines in optical spectra are produced by electrons jumping between different atomic energy levels. Spectroscopy of course remains a key weapon in the astrophysicist’s arsenal but nowadays the term is taken to mean any application of physical laws to astronomical objects. Over the years, astrophysics has gradually incorporated nuclear and particle physics as well as thermodynamics, relativity and just about every other branch of physics you can think of. I realise, however, that this isn’t really the answer to the question that potential students want to ask. What they (probably) want to know is what is the difference between undergraduate courses called Astronomy and those called Astrophysics? The answer to this one depends very much on where you want to study. Generally speaking the differences are in fact quite minimal. You probably do a bit more theory in an Astrophysics course than an Astronomy course, for example. Your final-year project might have to be observational or instrumental if you do Astronomy, but might be theoretical in Astrophysics. If you compare the complete list of modules to be taken, however, the difference will be very small.
Over the last twenty years or so, most Physics departments in the United Kingdom have acquired some form of research group in astronomy or astrophysics and have started to offer undergraduate degrees with some astronomical or astrophysical content. My only advice to prospective students wanting to find which course is for them is to look at the list of modules and projects likely to be offered. You’re unlikely to find the name of the course itself to be very helpful in making a choice. One of the things that drew me into astrophysics as a discipline (my current position is Professor of Theoretical Astrophysics) is that it involves such a wide range of techniques and applications, putting apparently esoteric things together in interesting ways to develop a theoretical understanding of a complicated phenomenon. I only had a very limited opportunity to study astrophysics during my first degree as I specialised in Theoretical Physics. This wasn’t just a feature of Cambridge. The attitude in most Universities in those days was that you had to learn all the physics before applying it to astronomy. Over the years this has changed, and most departments offer some astronomy right from Year 1. I think this change has been for the better because I think the astronomical setting provides a very exciting context to learn physics. If you want to understand, say, the structure of the Sun you have to include atomic physics, nuclear physics, gravity, thermodynamics, radiative transfer and hydrostatics all at the same time. This sort of thing makes astrophysics a good subject for developing synthetic skills while more traditional physics teaching focusses almost exclusively on analytical skills. Indeed, my first-year Astrophysical Concepts course is really a course about modelling and problem-solving in physics.Follow @telescoper
Since I’ve recently been officially awarded the title of Grumpy Old Man, I now feel I have the necessary authorization to vent my spleen about anything and everything that really irritates me.
This morning I got my regular monthly credit card statement, something likely to put me in a bad mood at the best of times. However, at the end of the itemized list of payments, I found the following:
WE ARE PHASING OUT CREDIT CARD CHEQUES. GOING FORWARD WE WILL NO LONGER ISSUE ANY CREDIT CARD CHEQUES.
I don’t actually care about the credit card cheques – they’re a ridiculously bad way of paying for things anyway – but what on Earth is the phrase going forward doing in that sentence?
I’ve taken a swipe at this monster once before, when I blogged about the Wakeham Review of Physics. The example I found then was
The STFC’s governance structure must be representative of the community it serves in order to gain stakeholders’ confidence going forward.
Going forward is one of those intensely annoying bits of office-speak that have spread like Swine ‘flu into the public domain. Pushing the envelope is another one. What does it mean? Why would anyone push an envelope?
Anyway, the worst problem with going forward is that it is now used almost universally in official documents instead of more suitable phrases, such as in future, or from now on. What particularly irritates me about it is that it is usually part of an attempt to present things in a positive light even when they clearly don’t involve any forward movement at all; often, in fact, quite the opposite. It is just one symptom of the insidious culture of spin that seems to be engulfing all aspects of public life, making it impossible to deliver even a simple message without wrapping it up in some pathetic bit of PR. Any kind of change – whether or not there’s any reason for it, and whether or not it improves anything – has to be portrayed as progress. It drives me nuts!
This sort of language is frequently lampooned by Laurie Taylor in his brilliant weekly column for the Times Higher. The Director of Corporate Affairs for the fictional Poppleton University, Mr Jamie Targett, contributes regularly to his column, always in meaningless business-oriented gibberish of this type. In fact, shortly after reading the Wakeham Review quoted above, I sent a letter to the Times Higher (which was published there) accusing Jamie Targett of moonlighting from his job at Poppleton to work on the Wakeham Report.
In the case of my credit card cheques, the implication is that the withdrawal of the service represents some sort of progress. In fact, it’s just to save money. A friend of mine who uses a local gym told me today that the gym had recently announced that
Going forward, members of the gym will no longer be supplied with free towels.
They went on to portray this as a great leap forward in caring for the environment, but in fact it is obviously just a way of saving their costs. Likewise with a sentence I found in a railway timetable recently:
Going forward the 8.15 train from Paddington will no longer call at Didcot Parkway
At least it’s still going to call at Didcot when it’s going backwards, which is the obvious implication of this sentence.
I’m glad I’m not alone in my disapproval of going forward. A year or so ago there was an article on the BBC website making much the same point. However, the amount of going forward has continued to increase. Robert Peston, the BBC business editor, once managed three going forwards in a four minute item on the Today programme.
The Science and Technology Facilities Council has obviously taken this phrase to heart. Their website is chock-a-block with going forward. Here’s an example (referring to a budget cut)
It will result in an approximately constant volume of project activity going forward ..
Obviously, once you start going forward there’s no going back, even if what lies in front of you is financial catastrophe…
PS. Feel free to add your own pet hates via the comments box going forward.
Undaunted by the ructions caused by my previous attempt (now removed) to have a bit of fun by posting a few clerihews, I’ve decided to try again but this time the target is cricketers.
Please keep them polite, unless they’re about Australians. Bonus points to anyone who manages one about Ben Hilfenhaus. Here are a few to get you started:
If you see Nathan Hauritz
Starting to glower, it’s
Because a humdinger
Hit his right index finger
Was man-of-the-match by dint of
Some excellent bowling
Well worth extolling
Went for a piddle
And when he came back
He’d quite lost the knack
Likes to go for the hook
But when it’s more full
He goes for the pull
May have raised a few doubts:
It was well worth a shout
But should have been “not out”..
Batted well in the dark
But looked like a chump
When he lost his off stump
Is not very fussy
Whether he edges or nicks
Or just wallops for six
Can never refuse
An offside dab
That the slips might just grab
Bravely marched forth
To face the England attack
But very soon marched back
Bowls like he has bunions
But let there be – please –
A bowler called Cheese
I was finishing off the draft of a paper the other day and remembered a little paper I did some time ago with a former PhD student of mine, Patrick Dineen. I thought it would be fun to put the pictures up here because it was one of those occasions when a little idea turns out much nicer than you expected…
What we had to start with was a collection of Faraday Rotation measurements of extragalactic radio sources dotted around the sky. Their distribution is fairly uniform but I hasten to add that it was not a controlled sample so it would be not possible to take the sources as representative of anything for statistical purposes.
Faraday rotation occurs because left and right-handed polarizations of electromagnetic radiation travel at different speeds along a magnetic field line. The effect of this is for the polarization vector to be rotated as light waves travel and the net rotation angle (which can be either positive or negative) is related to the line integral of the component of the magnetic field along the line of sight travelled by the waves. The picture below shows the distribution of sources, plotted in Galactic coordinates and coded black for negative and white for positive.
Some radio galaxies have enormously large Faraday rotation measures because light reaches us through regions of the source that have strong magnetic fields. However, for most sources in our sample the rotation measures are smaller and are thought to be determined largely by the propagation of light not through the emitting galaxy, near the start of its journey towards us, but through our own Galaxy, the Milky Way, which is near the end of its path.
If this is true then the distribution of rotation measures across the sky should contain information about the magnetic field distribution inside our own Galaxy. Looking at the above picture doesn’t give much of a hint of what this structure might be, however.
What Patrick and I decided to do was to try to make a map of the rotation measure distribution across the sky based only on the information given at the positions where we had radio sources. This is like looking at the sky through a mask full of little holes at the source positions. Using a nifty (but actually rather simple) trick of decomposing into spherical harmonics and transforming to a new set of functions that are orthogonal on the masked sky we obtained the following map:
(The technical details are in the paper, if you’re interested.) You probably think it looks a bit ropey but, as far as I’m concerned, this turned out stunningly well. The most obvious features are a big blue blob to the left and a big red blob to the right, both in the Galactic plane. What you’re seeing in those regions is almost certainly the local spur (sometimes called the Orion Spur; see below), which is a small piece of spiral arm in which the local Galactic magnetic field is confined. The blobs show the field coming towards the observer on one side and receding on the other. The structure seen is relatively local, i.e. within a kiloparsec or so of the observer.
I was very pleased to see this come out so clearly from an apparently unpromising data set, although we had to confine ourselves to large-scale features because of instabilities in the reconstruction of high-frequency components.
Following on from my previous posts (here and here) about the First Ashes Test in Cardiff, I can’t help adding a quick post about my visit to Lord’s yesterday (Saturday) to see the third day’s play at the Second Ashes Test.
The circumstances of the day’s play were a bit different to those at Cardiff, to say the least. On the first day England had batted first, starting in great style but then surrending some silly wickets. At the end of day 1 England were 364-6 with Strauss unbeaten on 161, the total score not being dissimilar to that on the first day at Cardiff. On day 2 Strauss was out almost immediately and it looked like it was going to be a disappointing day for England. But the last pair added 47 runs and England got to 425 all out. When the Austalians batted, however, England took control of the game, reducing them to 156-8 by the end of Day 2. I don’t know what got into the Ozzies on Friday but most of them lost their wickets to daft shots rather than good bowling. Perhaps it was nerves.
I arrived at Lord’s on Saturday morning, about 9.15. I have been to Lord’s a few times before but not recently and never as the guest of a member of the MCC (Anton). I joined the lengthy queue for member’s guests but made it into the ground in good time to find seats in the Warner Stand (next to the Pavilion) and then have a look around the cricket museum (where the Ashes themselves are on display).
It was a considerably posher occasion than Cardiff, with MCC ties, blazers and other paraphernalia on display. Picnic hampers were in evidence around the enclosure and champagne corks popped at regularly intervals. I contented myself, however, with lager and a bacon butty from the bar behind the stand.
Before the start of play the talk around the crowd was all about knocking over the last two Australian batsmen quickly and then enforcing the follow on. (If the team batting second doesn’t get within 200 runs of the team batting first then they can be required to bat again by the captain of the other team, which is called “following on”.) As it happened the tailenders clung on doggedly and it looked for a while they would close in on the 225 runs needed to avoid the follow-on. However, the last two wickets did eventually fall for a total of 215, leaving a deficit of 210 runs. England could have asked Australia to bat again but, to the consternation of most of the crowd, the England captain Andrew Strauss declined to enforce the follow-on.
There are pros and cons making a team follow on. One of the pros is that it maintains the momentum of the bowling performance. One of the cons is that the bowlers have already bowled an entire innings and have to do the same again almost immediately. They might be a bit tired, which could hand the advantage to the batting side if they can avoid losing early wickets. If the Australian batsmen had scored well after following on then England might also have needed to bat last on a pitch that may have started to break up. Batting last in a Test match is usually quite difficult.
I think Strauss is quite a cautious man and I think he decided that Australia’s strong batting display at Cardiff was enough evidence of ability for him not to want to risk them posting a huge second-innings score. England’s brittle second-innings batting performance at Cardiff provided further reason for not wanting to get into a run chase.
Strauss obviously wants to win the game but he also won’t want to lose it from this position. Test cricket isn’t just win-or-lose: there is also a third possibility, a draw (like at Cardiff). Often the biggest chance of winning a game is to give the side batting last a target that they might try to chase in risky fashion and get bowled out. However, if the batting side are good they might actually get the runs. Too big a target and they won’t be tempted to go for it, too small and they might well reach it. Maximizing the probability of winning does not miminize the probability of losing in this situation. If England simply didn’t want to lose they would bat out time, accumulate a huge total and give Australia insufficient time to make the runs. England might still win in such a strategy but a draw becomes much more probable.
It was clearly Strauss’ judgement was that England needed more runs but he wanted to get them quickly enough to declare and try to force a result in the two remaining days. The England batsmen came out just before lunch to try to push on to a huge lead. They started very brightly but unfortunately both openers Strauss and Cook were out shortly after lunch. There then followed a very turgid couple of hours when Pietersen and Bopara struggled to score runs. Pietersen, usually a prolific hitter, apeared to be struggling with his Achilles injury while Bopara is clearly out of touch at this level. Both batsmen scratched around unconvincingly for most of the session and then got themselves out.
At 174-4 it was looking like another collapse might be on the cards and the Australians might have to chase a total under about 400, which appeared to me to be eminently achievable with two full days play available after Saturday. However, Collingwood and (especially) Prior batted superbly well together taking the score to 260-5 and then Flintoff and Collingwood carried it onto 311 before Collingwood was out.
Many members of the crowd were screaming for a declaration now, but the weather intervened. It had been getting very dark for some time and finally started raining about 6.30. The umpires called off play for the day with England at 311-6, a lead of 521 with two days left to play, a good position to be in by any standards.
Unless the weather turns very bad over the next two days then it seems to me a draw is a very unlikely possibility now. If England declare overnight and Australia can bat for two days they will score enough runs to win the game, but in doing so they will have to surpass by some margin the highest ever total reached in the last innings to win a Test match. Frankly, if they can do that they deserve to win! On the other hand, England have plenty of time to bowl them out even if a bit is lost to the weather. I actually think Strauss’ decision to bat again was probably a good one and I think he should carry on batting tomorrow to get another 100 runs or so. There will still be time to bowl out the Ozzies, but the chance of them scoring enough to win the game is smaller.
I left the ground and walked to Paddington to get the train back to Cardiff and was home by 10pm. A very satisfactory day.
Postscript. I just looked at the scorecard of today’s play (Sunday) before posting this. England declared their innings closed on 311-6 and Australia went into bat this morning. At lunch they were 76-2. The odds are in favour of England winning, but Ponting is still in. It’s nicely poised.
Since the media have been banging on about it all week, as have various other bloggers, I suppose I should at least mention that today (16th July 2009) is the fortieth anniversary of the launch of NASA’s Apollo 11 mission which put the first man on the Moon. I’m reliably informed that the picture on the left shows the second man on the Moon, Buzz Aldrin, although I don’t think the costume gives much clue to the identity of the wearer.
My response to the media furore is muted because I’m decidedly ambivalent about the whole business of manned space exploration. I’m not going to be churlish and say that all the Apollo missions did was provide America with a much-needed propaganda victory during the Cold War. I think it’s true that putting a man on the Moon was a great achievement in terms of ingenuity and organization. It’s probably also true that it inspired many people to go into science who otherwise wouldn’t have done so. I’d even say that the sight of Earth from the Moon marked the beginning of a new age of awareness of the fragility of our own existence on our home planet and, perhaps even a step towards our coming-of-age as a species.
The reason I am ambivalent, however, is that the scientific returns from the Apollo missions were entirely negligible, at least in terms of value for money, partly because the Apollo missions weren’t really designed to do science in the first place and partly because the Moon just isn’t very interesting…
Mankind hasn’t returned to the Moon since the Apollo series came to an end. That’s not a matter for regret, just a reflection of the fact that there isn’t much to be found there. In those forty years astronomy and space science have moved on immeasurably through spaceborne observatories and unmanned probes. We have learned far more about the Universe those ways than could ever be achieved by sending a few people to collect rocks from a dull piece of rubble in our backyard. In the process, the Universe has grown in size relative to the scale possible to reach by human engineering projects. The last forty years has shown us that, in retrospect, going to the Moon wasn’t really all that impressive compared to what we can find out by remote means.
Unfortunately there appears to be an increasingly vocal lobby in favour of diverting funds from fundamental science into manned space exploration, much of it aimed at the goal of putting a person on Mars. This has not yet resulted in a commitment by the United Kingdom government to join in manned space exploration, but it is worrying that the Chief Executive of the Science & Technology Facilities Council is a failed astronaut who I fear sees this as an attractive option. Even more worryingly, Science Minister Lord Drayson seems to be keen too. It’s up to scientists to present the case to government for maintaining investment in fundamental science and against having the budget plundered to play Star Trek.
The European Space Agency‘s Aurora programme is intended to culminate with a manned trip to Mars, at an overall cost of over £30 billion. One of the arguments I hear over and over again in favour of this programme is that it will inspire young people to take up science, especially physics. Well, maybe. But people can’t become scientists unless they have the opportunity to learn science at School and there is a drastic shortage of physics teachers these days. What’s the point of being inspired if you can’t get the education anyway? You could train an awful lot of school teachers for a small fraction of the Aurora budget. And what’s the point of inspiring people to take up astronomy and space science when you’re also busy slashing the budget for research and ending the careers of those excellent scientists we’ve already got?
So by all means let’s celebrate the marvellous achievements of 1969, but let’s move on and not pretend that there is any good scientific reason for repeating them.