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The IAP at 75: The early history of our Institute

The IAP at 75: The early history of our Institute

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A grainy black-and-white photograph. A line of men stare into the camera. In the background, bare trees are outlined against the cold winter sky. The ground is thick with dead winter leaves. Four of the men are in suits and hats; three are labourers. One heavy-set man with a pencil moustache leans nonchalantly against a tree, another is there with his hands in his pockets. Behind them, a small truck is parked at an awkward angle. On the far left, one of the well-dressed men holds a pick in his hand. This man is Henri Mineur, who would in the following year become the first director of the IAP. The date is the 6 of January 1938: the date on which construction of the IAP started. Last Friday, we celebrated the institute’s 75th anniversary with a series of talks and presentations, and in addition a short film made by my friend Mr. Jean Mouette.

PremierCoupDePiocheIAP 1938
Henri Mineur starts construction work  for the IAP

The IAP was created out of an urgent need for new structures to carry out scientific research. In the early part of the 20th century, astronomy was undergoing a radical transformation. With the arrival of new instrumentation and new telescopes it became possible for the first time to apply our knowledge of physics to understand astrophysical processes and observation: the science of “astrophysics” came into being. For centuries, astronomy had been concerned with the positions and movements of stars and other objects, but with the arrival of richly quantitative measurements such as spectroscopy, which can provide detailed information concerning the chemical make-up of very distant objects, it became clear that a new approach was possible. However, it was not clear where this kind of new astronomy could be done in France – certainly not at the Universities which were orientated uniquely towards teaching, and saw no place for research. The observatories, steeped in centuries of positional astronomy (and still labouring to accomplish immense tasks like the “Carte Du Ciel”) were not quite ready for the transition.

One man, Jean Perrin, saw the need for a new national institution to carry out astrophysical research – an institution which would not be part of any existing structures but would be independent. A left-leaning government had just arrived in Paris, le “Front populaire”, and they fully supported Perrin’s idea. Jean Zay, a minister at the time, signed a decree on the 30th of October 1936 which led to the creation of the Observatoire de Haute Provence (the OHP, in some ways the “observing station” of the IAP), and the IAP itself, initally designated as a centre of research which would analyse data arriving from OHP and devise new instruments for the telescopes. The IAP would be constructed on a patch of ground in the Jardin de L’Observatoire, which the government had requisitioned for this purpose (leading to tensions between the Observatoire and the IAP which persisted for decades). The front populaire was uniquely disposed to these ideas. In fact, Perrin’s visits to the minister Jean Zay’s office invariably resulted in him receiving all the funds he requested.

Construction of the IAP started soon afterwards, and the building’s skeleton was in place by 1940: the interior, however was unfinished, and with the arrival of the Vichy regime and the German occupation, the construction was halted. Nevertheless, as Daniel Chalonge tells us after the war, building work was carried on in secret. Certainly other concerns occupied the scientists. Some left, others remained. Neither Perrin or Zey would survive the war: Perrin left for New York, where he died in 1942. Jean Zey was arrested by the Vichy government and later assassinated. In Paris, two astronomers, Holweck and Solomon, were arrested and executed by the Nazis. Henri Mineur himself was briefly imprisoned, before being released: he spent the remainder of the war in the resistance. Even astronomers long-dead suffered: the statue of Arago on the place Ile-de-Seine, in front of the site of the observatory, was melted down for bullets and shells. But finally, in 1944, some staff moved to the IAP. The building would not be completed until 1952 (and in the 1980s a third floor would be added to create the building as we know it today).

From almost the beginning, both theoretical and observational subjects were investigated at the IAP: spectrophotometric observations of the sun, stellar atmospheres, and every aspect of physical processes in an astrophysical context. We heard how Evry Schatzmann, aided by a large number of students, investigated almost every kind of astrophysical phenomena, and contributed greatly to the international reputation of our institute (but it made life difficult for the students: as they were all working on different topics, none could help each other). At the same time, machine shops and mirror polishing facilities, together with facilities for numerical calculations has ensured that new observations from OHP and elsewhere could be fully exploited. Today at IAP there are no longer any machine shops, but the importance of computing in astrophysics at the IAP has only grown in the intervening years.

How survey astronomy really got started, part 2: Astronomers realise how much work it takes

How survey astronomy really got started, part 2: Astronomers realise how much work it takes

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(This is the second part of a two-part article. Read the first part here).

Now skip ahead once again another ten or fifteen years. I found this fascinating book “The great star chart” written by a British astronomer, H.H. Turner, about the progress of the “Carte de Ciel” survey. Turner was an astronomer at the University of Oxford, and this short book is his account of the survey and the work that had been accomplished in Oxford by 1911.

It’s interesting to consider his book from a modern perspective: in those distant days our notions of the Universe were very different; cosmology did not exist as a science, Einstein had yet to formulate his theory of General Relativity, and we didn’t know what the true nature of the nebulae — those dim smudges which were picked up on the photographic plates from time to time — really were. That meant interpreting observations on the first deep plates quite challenging. In Turner’s book there is a lot of talk about the “fog” that might exist between the stars — that this fog might be part of an explanation why the numbers of stars varies so much from plate to plate. Were clusters of stars and were there really “stellar streams”? Similar confusion would exist in the coming years when we tried to understand the distribution of the counts of “nebulae” on the plates — was this variation again because of some kind of “fog” or was the distribution of the galaxies really non-uniform?

It turns out, that like a lot of things, the answer was a bit of both: there really is dust, but the distribution of stars and galaxies on the sky really is clustered, for the former because of the shape of our own milky way galaxy, and the latter because … well, that’s a much longer story. But it’s interesting to think of the parallels between counting stars to find out about the Milky Way and counting galaxies to find out about the Universe.

But getting back to the “carte du ciel”… There is the interesting table I have reproduced below, which shows the state of survey after ten years of operations, divided by into catalogue plates (the shallower survey) and “charts published” which are reproductions of the deeper survey plates.
Here it is:

Greatstarmapbein00turn pdf
Who actually got some work done

While some progress has been made in measurement, it is already clear at this stage that printing the plates will be very expensive: based on the techniques used in Paris to reproduce their part of the survey, Turner calculates that a complete set would weight over four tonnes, if it were ever to be completed. Printing the entire set would be staggeringly expensive.

The work was very time-consuming: it had taken four or five astronomers working full time almost ten years in Oxford to complete their part of the survey. The work was mind-numbingly repetitive, involving countless calculations to produce a catalogue for a single plate. Every position of every one of the stars on the plate was measured manually. To guard against errors, the plates were rotated 180 degrees and the measurement made a second time, and the positions compared. In those days “computers” were in fact room-full of workers with slide-rules. In fact, this chronic mismatch between the data-gathering capabilities of telescopes equipped with photographic plates and our ability to process it would last until the 1960s when digital computers finally became fast enough to handle the volumes of data involved. (In fact, the first extragalactic surveys also suffered from a lack of computing power, but that is a story for another day.) Given all this, it’s hardly surprising that very few observatories, more than ten years after the survey started, had completed their quota of plates. It’s interesting to note in passing that it is also said in some quarters the reason why Europe lagged America in the new science of observational cosmology was because all the astronomers on this side of the pond were tied up measuring positions of stars on thousands of photographic plates.

Turner also talks about cost.

Greatstarmapbein00turn pdf page 86 of 178
And how much it cost…

Well, not much has changed in survey operations in the last century or so: today staff costs and maintenance remains the most expensive items in running a survey. What is interesting from a contemporary point of view is that Turner talks about the trade-off between accuracy and speed: it’s obvious that in an undertaking this size, attempting to make the measurements to infinite precision would simply take infinitely long. Better do the job well enough to get the necessary precision — but not too well, otherwise it will never get finished. Tell that to a student finishing their first paper.
How could other observatories with smaller amounts of staff hope to complete such a massive enterprise? In fact, they couldn’t. The deeper survey plates were never printed out — it was simply too expensive. The rest of the survey, the astrographic catalogue, did actually get finished sometime in the 1950s, almost half a century after it started. In the 1980s and 90s, with the arrival of cheap and fast computing power, interest in the survey returned. One group of astronomers recalculated all the positions of the stars in the astrographic catalogue and compared them to those taken a century later with the Hipparcos satellite.

Another group turned to the photographic plates. Although plate-scanning equipment had been around for a while, it was much too slow to scan the plates of the survey, machines like the PdS microdensitometer would take one day to scan a single plate. Instead, another group of astronomers used off-the-shelf photographic film scanners to digitize some of the plates (this was in the last ten years) and compare them to more recent catalogues. In both cases, the age of the old plates becomes their greatest asset, providing an enormous baseline to measure the motions of stars in our galaxy…

Today, the carte du ciel is one of the major attractions at the “journee du Patrimoine” at the observatory. In fact, here you can see interested members of the public waiting to visit the old rusting domes of the carte du ciel this year just to hear this story that I’ve been telling you…

IMG 3138
The public visits the “carte du ciel”! 

We are just getting started. The Gaia satellite will be launched in the next month or so and will provide the most precise measurements of untold numbers of stars in the Milky Way.  Euclid,  further down the line, will do the same thing for galaxies. But we had better make sure the astronomers are properly motivated and that there are enough resources in place to complete the project, and actually do science with the data !

On Perec's "La vie mode d'emploi"

On Perec's "La vie mode d'emploi"

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Last week I just finished, after a quite a few months (yes, it’s hard to concentrate on books these days with all these electronic distractions), George Perec’s massive book “La vie mode d’emploi”. Perec’s book is an encyclopaedic tome that probably is the closest thing in the French language I think to a Gaddis or a Pynchon that I’ve come across, at least in terms of scope. And certainly in terms of length (more than 600 pages long). And written in a French is which is pretty damn obscure — I did have frequent recourses to asking ML “what does that word mean”?

The book describes all the inhabitants of a Parisian apartment building situated on the fictional Rue Simon-Crubeiller. And I when I say all the inhabitants, I mean all those who lived there from the building’s construction to around the mid 1970s — everyone who has lived in each apartment of each floor of the building. The book features not only an index, but also a chronological list of all the major events of the book, as well as a list of all the many stories that Perec tells us — by story, I mean here a short history or “fait divers” in most cases lasting no more than a few pages. And usually, but always, often ending badly or surprisingly.

All classes of characters swarm through the pages of Perec’s book — artists, confidence tricksters, millionaires, accountants, doctors, scholars, scientists. Perec fills his book with spurious scholarship, made-up citations from imaginary specialists of every field of human knowledge. Many characters spend their entire lives of fruitless quests that often end in failure, pursuing impossible endeavours. He includes everything. There are endless enumerations of every object found in the cellars of certain apartments. Paintings and interior decorations are described in excruciating detail. Not only the paintings themselves, but also the stories which take place inside the paintings. At one point, all the objects found in the stairway of the building over the last few decades is listed. Many of the characters know other characters in the building, but many others live separate lives. The events described in the book cover the four corners of the Earth, although we never leave rue Simon-Crubellier.

The main story running through the book is that of English billionaire Percival Bartelbooth, whose life’s work consists of a decades-long project to travel the four corners of the world (staying away from Paris for almost twenty years I think) and paint a series of watercolours in different seaside spots; back in Paris at rue Simon-Crubeiller, artisan Gaspard Winckler, on the orders of Bartelbooth, transforms each of these painting into a complicated jigsaw puzzle. For the next twenty years, Bartelbooth devotes all his energies to solving these puzzles; as each one is solved, he returns to the place where he first painted the picture and dissolves it, leaving a blank sheet of paper. Yup: I’m reminded of Beckett: everything we do in life is a means to avoid boredom.

Reading the book I couldn’t help thinking of the building I was reading it in: our building here at Avenue Rene-Coty was built at around the same time as Perec’s fictional building at 11, Rue Simon-Crubeller. Both of them are Haussmannien structures, built during the great housing boom in Paris at the end of the 19th century. Although, unlike Perec’s building, the most of the apartments in the building here have remained in the same family since its construction — talk about a particularly astute purchase, given that most of the apartments today in this seven-floor building are now worth more than 400,000 euros. I wonder what are all the stories of all the people who have lived here over the last 150 or so years?

Linking all these chaotic stories together is impossible — there is no thread running through them all. Well, that is real life, after all, where the people in the 7th floor may not necessarily know what happens on the ground floor. Links go unmade, after all. Perec does not make any attempt to step out from behind the curtain and tell us what it means. It doesn’t mean anything — we not in a novel, after all…

Descending beneath Paris: second part, at minus 25

Descending beneath Paris: second part, at minus 25

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The first impressions deep underground are always the same: it’s damp, cold and dark. Wellington boots are an essential element of clothing. The tunnels are very close to the level of the water table, and flooding is frequent. In certain tunnels the water level can easily reach waist level, although thankfully we avoided those. The water is a silty white colour, full of limestone dust.

But passing through the hole, further into the tunnel, you should pause and look around: the surface of the walls are smooth and well-preserved. Here, we were at almost the southern limit of this particular segment of the network, and we would have several kilometers to march before we got to where we wanted to be — near Denfert Rochereau, underneath my house, near the Observatory.

The underground passageways for the most part follow faithfully the above-ground streets, as a consequence of an arcane part of French law: anyone who owns a bit of land on the surface also owns what is below. So no boring tunnels under other people’s houses: the tunnels would have to be where the streets already were. At times, this leads to some strange effects, as the tunnels in places were constructed hundreds of years ago and were given the names of above-ground streets which no longer exist, or which do exist but which changed their names.

We followed one such street, the Avenue D’Orlean, which is now the Avenue du General le Clerc at street level. Walking down the narrow tunnel of course I kept my eyes to the ground but my friend leading us was inspecting carefully every inch of tunnel and ceiling. He showed me an inscription on the wall, some ancient graffiti — someone had scrawled “la republique ou la mort” — ancient revolutionary graffiti dating back a century or two. Above ground, everything changes, but down here at minus twenty five metres below, all is frozen preserved, perhaps like astronaut footsteps on the surface of the moon.

republiqueoulamort.jpeg

We made a tour of a few of the more well known sites in the 14th — old rooms packed to the ceiling with ancient human bones, student wall murals dating back a few decades, plaques proudly announcing to a public that hasn’t been down here for a century or more the names of the engineers who built the walls and tunnels and pillars absolutely essential to keep the new Paris metro disappearing into a large hole. For almost any construction work to be carried out in Paris one of the first things one must do is find out just what is exactly beneath your feet, and build down there, too.

We emerged into the fading evening light after spending around eight hours underground. It is always strange be once more in a world with light and colour where there are trees which move in soft summer breezes and one can hear the distant sounds of the city, birds singing, people talking, cars in the street. All so different from the silent, dark, frozen parallel Paris which we left behind but which remains very close…