While watching the CD of “The Race for the Double Helix”, I noticed a scene where the brilliant X-ray diffraction expert, Rosalind Franklin (who provided the crucial observational evidence that led to the structure of DNA) is discussing her work with a French scientist. When commiserated with by her colleague about the complex and tedious “Patterson Calculation” she was undertaking to convert measurements of photographic diffraction patterns into clues to the structure of the molecule, she refers to it as “like mapping infinity’. She is speaking French, but that’s how the film dubbers translate it. I understand just enough French to hear that her actual words are “une carte du ciel”–”a map of heaven”.

The Carte du Ciel was an ambitious celestial mapping project initiated by French astronomers late in the 19th century, when it was realized photography provided a means of highly precise positional measurements of millions of very faint stars. Only a few stars had been measured up to then using mechanical-optical methods, but astronomers realized that this precise survey work was the observational basis that underlies all our astronomical inferences. A consistent, comprehensive catalog of millions of stars positionally accurate to high precision over the whole sky, would be an invaluable baseline database for parallax and proper motion studies which could be undertaken by future generations comparing new data with the old. There is an excellent Wikipedia article on the Carte du Ciel for those of you interested in the technical details.

The French lobbied observatories worldwide to get involved in this project, which involved taking thousands of narrow-field long time exposure photographs of the entire sky, a task whose sheer magnitude could only be realized as a cooperative, international effort. The French led with a set of specifications and standards for the photography and the data reduction, and coordinated everyone involved to produce uniform and consistent products: The Carte du Ciel and the Astrographic Catalogue.

Needless to say, the project was never completed. The logistics and management led to unforeseen consequences; storage of thousands of bulky glass plates quickly became a problem, and astronomers resented yielding valuable telescope time to an undertaking that might not produce results for decades, if ever. And of course, rapid advances in telescope and photographic technology quickly outpaced the original specifications. The data was obsolete before it was published. For one thing, the real sexy discoveries were now being done in astrophysics using spectroscopy, not astrometrics. The Americans, with their endless supplies of money and enormous, fast, reflector light-buckets were taking over leadership of the field. No one wanted to spend money on small aperture, expensively figured, long focus, refractors specialized for astrometry.

The project eventually bogged down. Although much useful work was done, and it was done meticulously, the original concept of an all-sky deep positional database was never realized. The data gathered was valuable, and fortunate is the astronomer today who is working in an area where he can compare his new data with archival Carte du Ciel imagery. In proper motion work, the time between exposures is the most valuable single parameter. The older a photographic plate is, the more time has elapsed to reveal minute motions or gradual changes in brightness..

But most important were the unanticipated consequences. French astronomy never recovered its leadership position, they started suffering losses in funding, technology, and expertise which were being consumed by the Carte du Ciel. The inevitable brain drain did the rest.

In a side note, in spite of her acknowledged contribution, Franklin never got to share the Nobel Prize that was eventually awarded to Wilkins, Watson and Crick for the DNA work. She died soon after of cancer, (perhaps because of her constant exposure to X-rays?) and the Nobel is not awarded posthumously. The infamous Patterson Calculation is no doubt today available as laptop software that can run in seconds.