The Crowd and the Cosmos: Adventures in the Zooniverse

by Lintott, Chris

  sands of galaxies, resulted in something that appeared significant.

  Lots of explanations have been proposed over the years for

  this surprising result. Perhaps it’s something to do with the fact

  that most Galaxy Zoo classifiers read from left to right. We

  should probably check by asking the same question of Hebrew

  or Arabic speakers. Perhaps it’s something to do with what’s

  known as the silhouette illusion.† An image of a pirouetting

  dancer created by Flash artist and designer Nobuyuki Kayahara,

  this figure has the power to distract an entire lecture audience

  who will be mystified by their inability to agree on the direction

  * This topological solution sounds deep and profound, but was, I suspect, a sign of desperation at explaining such a ridiculous result.

  † .

  68 The Crowd and The Cosmos

  of spin. Stare at the figure long enough, and you will see it flip

  between clockwise and anticlockwise rotation as your brain

  changes its mind about how to translate this two-dimensional

  image into three-dimensional space.

  Something similar might well be happening as we view the

  galaxy images, but as astronomers I’m afraid to say that the

  explanation wasn’t nearly as important to us as the fact that we

  could measure the bias by looking at the differences in classifica-

  tions between the real images and the mirrored ones, and get on

  with science as a result. By doing so, we found that spiral galaxies

  which are close to each other are most likely to be spinning in the

  same direction, suggesting that they inherit their spin from the

  larger-scale structure around them and discrediting an older

  idea, which suggested that they could spin each other in opposite

  directions.

  Michael Longo wasn’t hugely impressed with our results, if

  reports of people who’ve talked to him are to be believed. To give

  him credit, he went back and redid his experiment with ran-

  domly rotated images of galaxies, deriving what appears at first

  glance to be a significant result which has been published in a

  journal. I haven’t had time to dig into the details, but suffice it to say that I’d be very, very surprised if the Universe turns out to

  prefer anticlockwise to clockwise galaxies. Such quibbles aside,

  we were pretty happy. We’d managed to detect a subtle effect,

  and get decent science out of the resulting data. More to the

  point, it was clear that the volunteers taking part in Galaxy Zoo

  could contribute high-quality classifications. It was time to go

  looking for the unusual galaxies that had inspired us to build and

  launch the project in the first place—including star-forming and

  therefore blue ellipticals.

  The hunt for these systems was now reduced to writing a data-

  base query, something that took seconds and which no one out-

  The Crowd and The Cosmos 69

  Figure 12 The IRAM 30-metre telescope, near the Sierra Nevada Ski

  Station above Granada. It has the best food of any observatory I’ve been to.

  side of a science fiction film can make dramatic. The results,

  though, were eye-opening; we found plenty of ellipticals with

  star formation rates that seemed to exceed the Milky Way’s. Our

  galaxy turns one or two solar masses worth of gas and dust into

  stars each year, but some of these systems were reaching rates of

  fifty or more. They were less massive than the average elliptical,

  but otherwise seemed perfectly normal. Best of all, the careful

  calibration we’d been able to do with the Galaxy Zoo results

  allowed us to be sure that for most of them it wasn’t that we’d

  missed spiral arms that were too distant or faint to be seen. These

  were really star-forming ellipticals, and now we knew they were

  there we could point telescopes at them.

  The telescope of choice was the IRAM radio telescope

  (Figure 12), the pride and joy of the Institut de Radioastronomie

  Millimétrique, situated among the slopes of a ski resort in the

  Sierra Nevada. IRAM is a strange place. In winter you reach the

  70 The Crowd and The Cosmos

  observatory by taking the ski lift among holidaymakers in

  designer ski gear, but the same climatic conditions that make for

  good skiing under clear blue skies make it a pretty good site for

  observing molecules. It’s not as high up, and thus not quite as

  good for sub-millimetre astronomy as Mauna Kea, but the tele-

  scope is twice the radius of the JCMT and the food is the best of

  any observatory I’ve ever been to. Skiing plans and culinary

  delights aside, access to IRAM was exciting because it allowed us

  to measure the amount of molecular gas present in our blue

  ellipticals. Molecular gas—primarily molecular hydrogen and

  carbon monoxide, the latter of which could be detected by the

  telescope—is necessary for star formation, and so this was the

  equivalent of checking the fuel gauge in the car. If there’s plenty

  of molecular gas, then your galaxy is good to go for billions of

  years of star formation. If supplies are running low, then it’s the

  end of the road unless new supplies can be taken on board.

  Even before grabbing IRAM data, we knew that not all the blue

  ellipticals were the same. We could tell, by paying close attention

  to their colours, that activity in most was on the decline, but the

  time since the peak of recent star formation could be anything

  from a few tens of millions of years to a billion or so. What we

  found from IRAM was that the timing mattered a great deal, with

  a sudden drop in the amount of molecular gas available occur-

  ring roughly 200 million years after the peak of star formation.

  Something must be happening to switch off star formation in

  these systems at roughly that timescale, either by heating the

  molecular gas so it would no longer show up in the observations

  we were making with this telescope, sensitive only to the emis-

  sion from cold gas, or by expelling it from the galaxy entirely.

  More importantly, these galaxies are providing us with a local

  laboratory to study the formation of ellipticals, a process much

  more common in the early Universe. Similar, parallel work by

  The Crowd and The Cosmos 71

  other members of the Galaxy Zoo team, particularly Karen

  Masters in Portsmouth, teased out what red spirals can tell us;

  these galaxies, too, are undergoing a transition from a star-

  forming phase to quiescence, though perhaps a less violent one

  than the galaxies we’d been studying at IRAM.

  By measuring the colour of a galaxy, which represents its

  current state, separately from its shape, which tells us about its

  longer history, Galaxy Zoo volunteers are providing real insight

  into the Universe. Because there’s a substantial population of

  each type of galaxy at all colours, we understand their more

  complex histories. As the indefatigable and indispensable mod-

  erator of the Galaxy Zoo forum, Alice Sheppard, pithily wrote:

  ‘Ellipticals are red. Spirals are blue. Or at least so we thought until Galaxy Zoo.
’ We know things now we didn’t just a few years ago,

  all because hundreds of thousands of people clicked on a website.

  3

  NO SUCH THING AS

  A NEW IDEA

  My idea of what constitutes recent history might have become

  slightly skewed after so much time spent thinking about

  the Universe. I consider the ‘present day’ to be an epoch lasting at

  least for hundreds of millions of years, and I spend most of my

  time worrying about things that happened billions of years ago.

  I therefore haven’t spent much time recently thinking about the

  end of the Austrian war of succession, one of the many conflicts

  that rolled across the European continent in the seventeenth and

  eighteenth centuries. Part of a series of conflicts which were triggered by disputes over the succession to the Habsburg Empire, it was missing from my school history syllabus (as was any knowledge of the details of the Habsburg Empire that shaped the political map of Europe for centuries, or indeed of anything that happened over the channel between the time of the Roman

  Empire and the First World War). It must have felt more significant at the time. Indeed, so significant was it even for Britain, which one might have thought was nothing but a distant spectator, the end of eight years of war on the continent was enough to spark dramatic celebrations.

  74 No Such ThiNg aS a New ide a

  Figure 13 Green Park with ‘magnificent structure’, ready for the celebratory fireworks in 1749, which Benjamin Robins hoped to use for his study of ballistics.

  It is these celebrations, which took place in the summer of 1749

  (Figure 13), that account for what we remember of the war today,

  at least in the UK. The London festivities took place with a

  soundtrack by the composer of the age, Handel. His Music for the

  Royal Fireworks was a spectacular success then as now, with a dress rehearsal attended by more than 12,000 paying concert­goers,

  and the premiere in Green Park in the centre of London packed

  with celebrants. Green Park today is not exactly quiet, existing as

  it does primarily as a favourite spot for lunching office workers

  or for tourists who have been exhausted by their task of staring

  through the railings at Buckingham Palace, but the hubbub on

  the evening of the display must have been something else.

  Among the gathered crowds, one observer in particular would

  have had especial reason to anticipate the firework display, if not

  the music itself. His name was Benjamin Robins, and he was a

  42­year­old mathematician with a mission, informed by a taste

  No Such ThiNg aS a New ide a 75

  for tackling not obscure theorems but rather the practical problems of the age. His early work, which amounted to mathematical doodling around the foundations of Newton’s theory of gravity,

  had been published already in the Philosophical Transactions of the Royal Society, the world’s first scientific journal. He would thus have already been known to most of London’s scientific glitterati,

  and by the time of the Green Park fireworks he had been working

  on military problems for some time.

  Back in 1742 he had published a treatise on the topic of New

  Principles in Gunnery, demonstrating for the first time an apparatus, known as the ballistic pendulum, that could be used to measure

  the velocity of a bullet. The idea was simple, and the execution

  elegant. By allowing a bullet from a gun to strike a heavy pendulum, and then by observing the subsequent behaviour of the pendulum, the speed of the bullet could be calculated. Almost

  comically simple as an idea, Robins’ design remained in use as a

  matter of course until the nineteenth century, and it brought its

  inventor a certain measure of renown.

  It must have been a blow, therefore, when he failed in his application to be Professor of Artillery at the Royal Military Academy in Woolwich. A lesser man might have retreated back to the

  books, away from practical problems, but rather than simply

  give up Robins renewed his interest in the science of ballistics.

  Thanks to his pendulum, he knew how fast projectiles could

  travel, but not the other piece of information needed to predict

  their trajectories accurately—how high in the air did they get?

  The firework display of 1749, the apogee of a craze for such shows

  that had been steadily building over the previous century, provided a heaven­sent experiment for an ambitious student of ballistics. All that one needed to do was observe the same fireworks from as many far­flung places as possible; if the angle at which

  the rockets seemed to be flying and their apparent height could

  76 No Such ThiNg aS a New ide a

  be recorded at each location, Robins thought he could reconstruct their paths and understand their potential as weapons.

  The plan was simple, but Robins estimated that the rockets

  might be visible for up to forty miles away from the park. The

  accuracy of his experiment would depend on recording observations from as many places as possible, and even if that problem could be faced then the measurements would not be simple.

  Close to the launch site the rocket’s angle of attack could be estimated by eye, but more distant observers would have to record the position of the rocket as seen against the stars of the night

  sky or against the height of some distant building. The former

  method would require astronomical calculations to be completed, the latter would send observers, out after the show was over, across the fields to measure the height of their chosen landmark precisely along with the distance from their vantage point to the chosen reference point.

  Covering such a large area with trained observers was beyond

  the reach of the resources Robins had to hand, and he must have

  cursed the lack of a willing (or at least biddable) cadre of military cadets that the Woolwich position would have afforded him.

  Rather than give up he turned, as we did with Galaxy Zoo over

  250 years later, to help from a friendly public. Lacking the web,

  he used the Gentleman’s Magazine to advertise his scheme, one of a handful of early attempts to do science through what we’d now

  call crowdsourcing. The Gentleman’s Magazine was not such a bad choice; it was the first general purpose magazine to reach a large

  audience. It had already given Samuel Johnson his first regular

  paying gig, so clearly was home to an audience capable of recognizing intellectual heft and import as well as being widely distributed.

  What readers made of Robins’ instructions is uncertain. They

  were clear enough, if a little on the detailed side. Those between

  No Such ThiNg aS a New ide a 77

  fifteen and forty miles of London were instructed as follows (take

  a deep breath):

  Observing the angle which a rocket, when highest, makes with

  the horizon, is not difficult. For if it be a star­light night, it is easy to mark the last position of the rocket among the stars:

  whence, if the time of the night be known, the altitude of the

  point of the heavens corresponding thereto, may be found on a

  celestial globe. Or if this method be thought too complex, the

  same thing may be done by keeping the eye at a fixed place, and

  then observing on the side of a distant building, some known

  mark, which the rocket appears to touch when highest; for the

  altitude of that mark may be examined next day by a quadrant;

  or, if a level line be carried from the place where the eye was

  fixed to the point p
erpendicularly under the mark, a triangle

  may be formed, whose base and perpendicular will be in the

  same proportion as the distance of the observer from the fireworks, is to the perpendicular ascent of the rocket.*

  As I said, perfectly straightforward, but perhaps lacking in the

  necessary urgency and oomph to persuade the casual reader of a

  magazine many miles outside London to go and stand outside to

  get a poor view of a distant firework display. While I’m adopting

  the role of a critic and ignoring the historical distance of a couple of centuries, it seems to me unlikely that anyone would go out

  the next morning with a quadrant they happened to have handy

  in order to check the height of a building. Uncharitable, perhaps,

  but given that the pages of the Gentleman’s Magazine in subsequent months contain no reports from observers within fifty miles of

  the display, it is surely fair to call Robins’ scheme something

  other than a success.

  * Gentleman’s Magazine, v. 18, p. 488.

  78 No Such ThiNg aS a New ide a

  There was one report received, from a Welshman in Carmarthen

  who climbed a local hill having heard from the local press that

  the show from London might be spectacular. I love the idea of

  this man—identified by his signature only as Thomas ‘ap Cymra’

  (Tom the Welsh)—standing, squinting at the horizon, straining

  to pick out anything that might be a firework. His patience was,

  unbelievably, rewarded as he saw two flashes of light, which he

  estimated to be fifteen degrees above the horizon. Carmarthen is

  nearly 140 miles from London, so a successful sighting is either

  unlikely or clear evidence for profligate spending on a show that

  was intended primarily to entertain metropolitan crowds, not

  solitary Welshmen. Indeed, Thomas’ main point in his report is

  to complain about the cost of what he thought he saw. To add

  insult to injury, Robins didn’t believe him either, and when he

  published his results he used only the observations provided by a

  friend stationed in Clerkenwell, sixty times closer to the action

  than Thomas, concluding that rockets reached a height of just

  over 500 metres.

  The failure of Robins’ call for assistance led him to rely from