From Wikipedia, the free encyclopedia

Carte du Ciel ("Map of the Sky") was an international project to map the positions of millions of stars — that is to say, of all stars to the 11th or 12th magnitude. In English, the project was sometimes known as the Astrographic Chart.

It was begun in 1887 by Paris Observatory director Amédée Mouchez, who realized the potential of the new technology of photography to revolutionize the process of making maps of the stars. He conceived of a project that would take 22,000 photographic plates of the entire sky, each 2°×2°, and enlisted the aid of numerous observatories around the world, who were each assigned a separate section of the sky to work on.

The work involved two stages. In the first stage, astronomers determined precise positions of several thousand reference stars in various parts of the sky by timing their meridian transits. In the second stage, astronomers took photographic plates, and then the plates were turned over to a large number of semi-skilled female "computers" to determine the positions of the stars on each plate (before its modern meaning, the word "computer" meant a person who performs calculations). The "computers" would manually measure each star with respect to the dozen or so reference stars within that particular plate, and then perform calculations to determine the star's right ascension and declination.

Decades of labour were expended internationally before the project was superseded by modern astronomical techniques. The project was never completed, although a catalogue was published in 1958.

One problem was that the work took much longer than expected. For instance, the Algiers Observatory, which was the most active in the project, did not finish its allotted work until 1919. As originally envisaged, the project was meant to have taken only 10 to 15 years.

A more serious problem was that while French astronomers were preoccupied with this project, which required steady, methodical labor rather than creativity, in other parts of the world like the United States astrophysics was becoming far more important than astrometry. As a result, French astronomy fell behind and lagged for decades.

Although the project did result in the discovery of some double stars and stars with high proper motion, it is a fair assessment to say that the results were not commensurate with the vast amount of time and effort expended.

The laborious work once performed by the female "computers" is today done by electronic computers. Inexpensive software packages for home computers enable any amateur astronomer to determine precise positions for every star in an image in a fraction of a second.

• Turner, Herbert Hall. The Great Star Map, Being a Brief General Account of the International Project Known as the Astrographic Chart (London: John Murray, 1912).

• Histoire de l'observatoire de Toulouse (with section on the Carte du Ciel)