The insoluble pancake

Henry Joy McCracken: 1925-2014

May 31, 2014 H. J. McCracken Comments 0 Comment

Three weeks ago, after a long illness, my father, Henry Joy McCracken, died. Here are a few words for him:

What was the kind of him? He was always an old man to me. He disliked photographs. But there was one photograph in the family album I remember, two men under the burning sun: one of whom was my father. He seemed impossibly handsome and confident, smiling broadly at the camera. This was his great voyage, India. It was harder to travel then than today: a voyage was a sacrifice. He made himself an indentured man. He left for five years, came back in one: his father died, his plans were changed for him, he returned home. He never told me to come home, never told me that I should stay in Ireland, always said that I should leave, that it was essential to leave. He was proud of what Sinead and myself had done, of how we had left.

What was the kind of him? He was rigorous in his work, exacting. He took pride in the sharp edges and vertical plumb-lines. We left Cookstown to a new house for us he paid for himself with long hours hefting stone and granite under Tyrone’s low clouds. With him, I learned what real work was, passing many hours in damp graveyards. At lunch, we would eat sausage rolls from thermoses my mother had packed for us, sitting high in the lorry cabin as the rain rumbled on the roof. In his work, he was a man of habit: coffee, lunch times were regulated. Later, when we moved out to the country, I would wait uncertainly for the sound of the lorry in the driveway at the end of a sumer day: I would have to help unloading the lorry. Wheelbarrows, picks, buckets, trowels. One day I asked him: “but why doesn’t Sinead ever help?” His response, “Sinead’s a wee girl” didn’t explain anything to me.

What was the kind of him? Taciturn, quiet, but within him were bright fragments of words, there until the end, even when his illness had robbed all things around him of their meaning. Those shards of verse remained. “The moving finger writes” and having writ, it did move on. By the time I had left Ireland, I had heard these words so many times that I knew them too. “Can storied urn”, he said as the warm rain rolled across the fields, “back to its mansion”, as we hefted granite and limestone, “call the fleeting breath?”, stone and dust and gravel and concrete, “can honour’s voice” he murmured, “provoke the silent dust?” And there there were songs, too. “I’ll take you home again Kathleen” he would sing as we shifted gravel and white chips. Much later, “How can you get them back on the farm once they’ve seen Paris?” he would ask me, rhetorically, citing an old post-war song. Indeed.

What was the kind of him? The hard edges in him were dulled by illness and time. The last people that met him found him a soft-spoken charming man who liked a drink and liked, at times, to reminisce about his voyage, or the town that he lived in. Near the end, I would say to him, as he lay on his bed almost immobile, ‘It’s Henry Joy’ and his eyebrows would raise and that deep soft voice would repeat “Ah, Henry Joy” and for and instant there would be a tiny, tiny glimmer.

What was the kind of him? That was the kind of him.

The IAP at 75: The early history of our Institute

October 19, 2013 H. J. McCracken Comments 0 Comment

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.

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.

Interlude: Geneva-Paris

October 11, 2013 H. J. McCracken Comments 0 Comment

I’m on the train, gliding through mountains shrouded in mist and fog, not so far from the border between Switzerland and France. I’m returning from a short trip to Geneva and heading to Paris.

Even today, each place I visit is framed by the books I have read – too many, it seems. It’s the second time in a year I am in Geneva, but before that it was more than twenty years since I last visited. I am reminded of that short story by Borges where the older Borges meets himself, much younger, on a park bench overlooking the lake. What would I have said if I had met the younger H. J. McCracken in the streets of Geneva? Well, I know what he would have said to me: “Hey, what happened to the hair”? He might have also remarked on the wedding ring. But he would have probably been relieved to learn that I was now a astronomer and living in Paris and that I had actually managed to find someone like Marie-Laure. All that would probably have seemed incredible to him then, in that distant summer of 1991 when I first travelled to “continental Europe” as I sometimes called it back then. I don’t think I would have had any useful advice to offer him, other than “keep working, you’ll get there, and along the way you’ll find out where you’re supposed to go”.

I spent three months as an assistant at a research lab in Zurich, the ETH. It was my first to the vast European continent. I was so excited at the prospect of that trip and spending so much time there that for weeks beforehand my dreams were filled with jumbled-up impressions of what I imagined that these cities I had never visited before would look like. Once I arrived, I was disorientated and charmed – I had never seen before a city that was actually pleasant to look at (my thoughts on Zurich have changed a bit in the meantime, when I returned there in 2012: that, again, is a story for another day). On the weekends, I would take the train and visit Swiss cities or wander the streets of Zurich. The last two weeks before I returned to Manchester I made a short tour of a few European cities, strangely selected in retrospect – Munich, Prague, Strasbourg and Paris. I did not visit Italy. I harboured a lingering suspicion of the debauched South at that time in my life, probably as side-effect of my isolated adolescence in rural Ireland. Back in Manchester I vainly searched for traces of the life I had seen in Switzerland, which in general meant lingering for hours over milky tea in greasy spoon cafes after I had eaten beans on toast and imagining that I was in a cafe overlooking Lake Zurich.

It’s strange the details I recall from that summer. I actually remember the first espresso I ever drank. I had somehow been given a ticket for a free drink at Zurich cafe (remember, I am a student coming from Manchester at this point). I presented my ticket, expecting a large mug of coffee I think, and then being surprised to see … what? The smallest cup of coffee I had ever seen in my life. An espresso. I didn’t understand. I didn’t appreciate it either – it probably wasn’t a very good espresso. Ah, I would have to wait a decade or so before I really appreciated espresso.

To return to the present: this afternoon at IAP we are celebrating the institute’s 75th anniversary. It’s interesting to think about how astronomy has changed in intervening years, and to imagine what will be the state of affairs will be in another 75 years. Reporting back soon…

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

October 6, 2013 H. J. McCracken Comments 0 Comment

(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:

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…

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 !