Carte du Ciel
Encyclopedia
The Carte du Ciel and the Astrographic Catalogue (or Astrographic Chart) were two distinct but connected components of a massive international astronomical project, initiated in the late 19th century, to catalogue and map the positions of millions of star
s as faint as 11th or 12th magnitude. Twenty observatories from around the world participated in exposing and measuring more than 22,000 (glass) photographic plates in an enormous observing programme extending over several decades. Despite, or because of, its vast scale, the project was only ever partially successful – the Carte du Ciel component was never completed, and for almost half a century the Astrographic Catalogue part was largely ignored. However, the appearance of the Hipparcos Catalogue in 1997 has led to an important development in the use of this historical plate material.
director Amédée Mouchez
, who
realized the potential of the new technology of photography to revolutionize the process of making maps of the stars. As a result of the Astrographic Congress of more than 50 astronomers held in Paris in April 1887, 20 observatories from around the world agreed to participate in the project, and two goals were established:
For the first, the Astrographic Catalogue, the entire sky was to be photographed to 11 mag to provide a reference catalogue of star positions that would fill the magnitude gap between those previously observed by transit and meridian circle instrument observations down to 8 mag – this would provide the positions of a reasonably dense network of star positions which could in turn be used as a reference system for the fainter survey component (the Carte du Ciel). Different observatories around the world were charged with surveying specific declination zones (see table). The Astrographic Catalogue plates, of typically 6 minutes exposure, were in due course photographed, measured, and published in their entirety. They yielded a catalogue of positions and magnitudes down to about 11.5 mag, and the programme was largely completed during the first quarter of the 20th century.
For the second goal, a second set of plates, with longer exposures but minimal overlap, was to photograph all stars to 14 mag. These plates were to be reproduced and distributed as a set of charts, the Carte du Ciel, in contrast to previous sky charts which had been constructed from the celestial coordinates of stars observed by transit instruments. Most of the Carte du Ciel plates used three exposures of 20 minutes duration, displaced to form an equilateral triangle with sides of 10 arcsec, making it easy to distinguish stars from plate flaws, and asteroids from stars.
A fascinating contemporary account of this vast international astronomical collaboration, published in 1912, is given by H.H. Turner, then Savilian Professor of Astronomy at Oxford University. Other aspects are covered in various papers in the Proceedings of IAU Symposium Number 133 held in 1988.
in France, with others coming from the factory of Howard Grubb of Dublin
. These telescopes were termed normal astrograph
s with an aperture of around 13 inches (330 mm) and a focal length of 11 feet (3.4 m) designed to create images with a uniform scale on the photographic plate of approximately 60 arcsecs/mm wile covering a 2° × 2° field of view. Each observatory was assigned a specific declination zone to photograph. The first such plate was taken in August 1891 at the Vatican Observatory
(where the exposures took more than 27 years to complete), and the last in December 1950 at the Uccle Observatory (Bruxelles), with most observations being made between 1895 and 1920. To compensate for plate defects, each area of the sky was photographed twice, using a two-fold, corner-to-centre overlap pattern, extended at the zone boundaries, such that each observatory's plates would overlap with those of the adjacent zones. The participating observatories agreed to use a standardized telescope so that all plates had a similar scale of approximately 60 arcsec/mm. The measurable areas of the plates were 2.1°×2.1° (13 cm×13 cm), so the overlap pattern consisted of plates that were centred on every degree band in declination, but offset in right ascension by two degrees. Many factors, such as reference catalogue, reduction technique and print formats were left up to the individual institutions. The positional accuracy goal was 0.5 arcsec per image.
Plate measurement was a protracted affair, with measuring done by eye and recorded by hand. The plates were turned over to a large number of semi-skilled "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
. The original goal of 11 mag for the limiting magnitude was generally surpassed, however, with some observatories routinely measuring stars as faint as 13 mag. In total, some 4.6 million stars (8.6 million images) were observed. The brightest stars were over-exposed on the plates, not measured, and therefore missing in the resulting catalogues. The plate measurements (as rectangular coordinates), as well as the formulae to transform them to equatorial coordinates, were published in the original volumes of the Astrographic Catalogue, although the accompanying equatorial coordinates are now of only historical interest. Publication of the measurements proceeded from 1902 to 1964, and resulted in 254 printed volumes of raw data.
For decades the Astrographic Catalogue was largely ignored. The data were difficult to work with because they were available neither in machine-readable form nor in equatorial coordinates. Decades of labour were expended internationally before the project was superseded by modern astronomical techniques. One problem was that the work took much longer than expected. As originally envisaged, the project was meant to have taken only 10 to 15 years. A more serious problem was that while many European astronomers were preoccupied with this project, which required steady, methodical labor rather than creativity, in other parts of the world notably the United States astrophysics
was becoming far more important than astrometry
. As a result, French astronomy in particular fell behind and lagged for decades.
), and many zones were either not completed or properly published. The plates which were taken generally still exist, but cover only half of the sky. They are typically archived at their original observatories. A very few plates have recently been re-measured and re-analysed with the availability of the Hipparcos Catalogue data (see below).
space astrometry satellite, allowing high accuracy proper motions to be derived for 2.5 million stars. Specifically, the Astrographic Catalogue positions were transferred from the decades-old printed catalogues into machine readable form (undertaken at the Sternberg Astronomical Institute
in Moscow under the leadership of A. Kuzmin) between 1987–94. The data were then reduced anew (at the US Naval Observatory in Washington under the leadership of Sean Urban), using the reference stars measured by the Hipparcos
astrometry satellite. The 120,000 highest accuracy stars from the Hipparcos Catalogue were used to establish a detailed reference framework at the various epochs of the Astrographic Catalogue plates, while the 2.5 million stars in the Tycho-2 Catalogue provided a dense reference framework to allow the plate distortions to be accurately calibrated and corrected. The proper motions of all the Tycho Catalogue stars could then be derived especially thanks to the Astrographic Catalogue, but additionally using star positions from more than 140 other ground-based catalogues. Aside from the 120,000 stars of the Hipparcos Catalogue itself, the resulting Tycho-2 Catalogue (compiled at the Copenhagen University Observatory
under the leadership of Erik Høg) is now the largest, most accurate and most complete, star catalogue of the brightest stars on the sky. It is currently the basis for deriving positions for all fainter stars on the sky. Sean Urban of the US Naval Observatory wrote in 1998:
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
s as faint as 11th or 12th magnitude. Twenty observatories from around the world participated in exposing and measuring more than 22,000 (glass) photographic plates in an enormous observing programme extending over several decades. Despite, or because of, its vast scale, the project was only ever partially successful – the Carte du Ciel component was never completed, and for almost half a century the Astrographic Catalogue part was largely ignored. However, the appearance of the Hipparcos Catalogue in 1997 has led to an important development in the use of this historical plate material.
| Observatory | Declination Declination In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and... | Greenwich Royal Observatory, Greenwich The Royal Observatory, Greenwich , in London, England played a major role in the history of astronomy and navigation, and is best known as the location of the prime meridian... | +90° | +65° | 1892–1905 | 179,000 | |
|---|---|---|---|---|---|---|---|
| Vatican | +64° | +55° | 1895–1922 | 256,000 | |||
| Catania | +54° | +47° | 1894–1932 | 163,000 | |||
| Helsingfors | +46° | +40° | 1892–1910 | 159,000 | |||
| Potsdam | +39° | +32° | 1893–1900 | 108,000 | |||
| Hyderabad north | +39° | +36° | 1928–1938 | 149,000 | |||
| Uccle | +35° | +34° | 1939–1950 | 117,000 | |||
| Oxford 2 | +33° | +32° | 1930–1936 | 117,000 | |||
| Oxford 1 | +31° | +25° | 1892–1910 | 277,000 | |||
| Paris Paris Observatory The Paris Observatory is the foremost astronomical observatory of France, and one of the largest astronomical centres in the world... |
+24° | +18° | 1891–1927 | 253,000 | |||
| Bordeaux | +17° | +11° | 1893–1925 | 224,000 | |||
| Toulouse | +10° | +05° | 1893–1935 | 270,000 | |||
| Algiers Algiers Observatory The Algiers Observatory was built in the late nineteenth century in the Algiers suburb of Bouzaréah. It participated in the Astrographic Catalogue project, taking the zone between -2 and +4 degrees to expose 1,260 plates between the years 1891 and 1911... |
+04° | −02° | 1891–1911 | 200,000 | |||
| San Fernando | −03° | −09° | 1891–1917 | 225,000 | |||
| Tacuba | −10° | −16° | 1900–1939 | 312,000 | |||
| Hyderabad south | −17° | −23° | 1914–1929 | 293,000 | |||
| Córdoba Argentine National Observatory The Argentine National Observatory, today The Astronomical Observatory of Córdoba, was founded on 24 October 1871, by Argentine president Domingo F. Sarmiento and the North American astronomer Benjamin Apthorp Gould.... |
−24° | −31° | 1909–1914 | 309,000 | |||
| Perth | −32° | −37° | 1902–1919 | 229,000 | |||
| Perth/Edinburgh | −38° | −40° | 1903–1914 | 139,000 | |||
| Cape Town | −41° | −51° | 1897–1912 | 540,000 | |||
| Sydney Sydney Observatory Sydney Observatory is located on a hill now known as 'Observatory Hill' in an area in the centre of Sydney. The site evolved from a fort built on 'Windmill Hill' in the early 19th century to an astronomical observatory during the nineteenth century... |
−52° | −64° | 1892–1948 | 430,000 | |||
| Melbourne Melbourne Observatory Melbourne Observatory was founded in 1862 to serve as a scientific research institution for the rapidly growing city of Melbourne, the capital of the colony of Victoria. The observatory was tasked by the Victorian government with maintaining an accurate time reference for the colony through... |
−65° | −90° | 1892–1940 | 218,000 | |||
Origins and Goals
A vast and unprecedented international star-mapping project was initiated in 1887 by Paris ObservatoryParis Observatory
The Paris Observatory is the foremost astronomical observatory of France, and one of the largest astronomical centres in the world...
director Amédée Mouchez
Amédée Mouchez
Amédée Ernest Barthélemy Mouchez was a French naval officer who became director of the Paris Observatory and launched the ill-fated Carte du Ciel project in 1887.-Life:...
, who
realized the potential of the new technology of photography to revolutionize the process of making maps of the stars. As a result of the Astrographic Congress of more than 50 astronomers held in Paris in April 1887, 20 observatories from around the world agreed to participate in the project, and two goals were established:
For the first, the Astrographic Catalogue, the entire sky was to be photographed to 11 mag to provide a reference catalogue of star positions that would fill the magnitude gap between those previously observed by transit and meridian circle instrument observations down to 8 mag – this would provide the positions of a reasonably dense network of star positions which could in turn be used as a reference system for the fainter survey component (the Carte du Ciel). Different observatories around the world were charged with surveying specific declination zones (see table). The Astrographic Catalogue plates, of typically 6 minutes exposure, were in due course photographed, measured, and published in their entirety. They yielded a catalogue of positions and magnitudes down to about 11.5 mag, and the programme was largely completed during the first quarter of the 20th century.
For the second goal, a second set of plates, with longer exposures but minimal overlap, was to photograph all stars to 14 mag. These plates were to be reproduced and distributed as a set of charts, the Carte du Ciel, in contrast to previous sky charts which had been constructed from the celestial coordinates of stars observed by transit instruments. Most of the Carte du Ciel plates used three exposures of 20 minutes duration, displaced to form an equilateral triangle with sides of 10 arcsec, making it easy to distinguish stars from plate flaws, and asteroids from stars.
A fascinating contemporary account of this vast international astronomical collaboration, published in 1912, is given by H.H. Turner, then Savilian Professor of Astronomy at Oxford University. Other aspects are covered in various papers in the Proceedings of IAU Symposium Number 133 held in 1988.
The Astrographic Catalogue
For the Astrographic Catalogue, 20 observatories from around the world participated in exposing and measuring more than 22,000 glass plates (see table). Around half of the observatories ordered telescopes from the Henry brothers (Paul and Prosper)Paul Henry and Prosper Henry
Paul-Pierre Henry and his brother Mathieu-Prosper Henry were French opticians and astronomers....
in France, with others coming from the factory of Howard Grubb of Dublin
Sir Howard Grubb, Parsons and Co. Ltd.
Sir Howard Grubb, Parsons and Co. Ltd. was a telescope manufacturer, more commonly known as Grubb Parsons based in Newcastle upon Tyne.-History:...
. These telescopes were termed normal astrograph
Astrograph
An astrograph is a telescope designed for the sole purpose of astrophotography. Astrographs are usually used in wide field surveys of the night sky as well as detection of objects such as asteroids, meteors, and comets.-Design:...
s with an aperture of around 13 inches (330 mm) and a focal length of 11 feet (3.4 m) designed to create images with a uniform scale on the photographic plate of approximately 60 arcsecs/mm wile covering a 2° × 2° field of view. Each observatory was assigned a specific declination zone to photograph. The first such plate was taken in August 1891 at the Vatican Observatory
Vatican Observatory
The Vatican Observatory is an astronomical research and educational institution supported by the Holy See. Originally based in Rome, it now has headquarters and laboratory at the summer residence of the Pope in Castel Gandolfo, Italy, and an observatory at the Mount Graham International...
(where the exposures took more than 27 years to complete), and the last in December 1950 at the Uccle Observatory (Bruxelles), with most observations being made between 1895 and 1920. To compensate for plate defects, each area of the sky was photographed twice, using a two-fold, corner-to-centre overlap pattern, extended at the zone boundaries, such that each observatory's plates would overlap with those of the adjacent zones. The participating observatories agreed to use a standardized telescope so that all plates had a similar scale of approximately 60 arcsec/mm. The measurable areas of the plates were 2.1°×2.1° (13 cm×13 cm), so the overlap pattern consisted of plates that were centred on every degree band in declination, but offset in right ascension by two degrees. Many factors, such as reference catalogue, reduction technique and print formats were left up to the individual institutions. The positional accuracy goal was 0.5 arcsec per image.
Plate measurement was a protracted affair, with measuring done by eye and recorded by hand. The plates were turned over to a large number of semi-skilled "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
Right ascension
Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...
and declination
Declination
In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...
. The original goal of 11 mag for the limiting magnitude was generally surpassed, however, with some observatories routinely measuring stars as faint as 13 mag. In total, some 4.6 million stars (8.6 million images) were observed. The brightest stars were over-exposed on the plates, not measured, and therefore missing in the resulting catalogues. The plate measurements (as rectangular coordinates), as well as the formulae to transform them to equatorial coordinates, were published in the original volumes of the Astrographic Catalogue, although the accompanying equatorial coordinates are now of only historical interest. Publication of the measurements proceeded from 1902 to 1964, and resulted in 254 printed volumes of raw data.
For decades the Astrographic Catalogue was largely ignored. The data were difficult to work with because they were available neither in machine-readable form nor in equatorial coordinates. Decades of labour were expended internationally before the project was superseded by modern astronomical techniques. One problem was that the work took much longer than expected. As originally envisaged, the project was meant to have taken only 10 to 15 years. A more serious problem was that while many European astronomers were preoccupied with this project, which required steady, methodical labor rather than creativity, in other parts of the world notably the United States astrophysics
Astrophysics
Astrophysics is the branch of astronomy that deals with the physics of the universe, including the physical properties of celestial objects, as well as their interactions and behavior...
was becoming far more important than astrometry
Astrometry
Astrometry is the branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. The information obtained by astrometric measurements provides information on the kinematics and physical origin of our Solar System and our Galaxy, the Milky...
. As a result, French astronomy in particular fell behind and lagged for decades.
The Carte du Ciel
The still-more-ambitious Carte du Ciel component of the programme was undertaken by some of the participating observatories, but neither completed nor even started by others. The charts proved to be excessively expensive to photograph and reproduce, generally via engraved copper plates (photogravurePhotogravure
Photogravure is an intaglio printmaking or photo-mechanical process whereby a copper plate is coated with a light-sensitive gelatin tissue which had been exposed to a film positive, and then etched, resulting in a high quality intaglio print that can reproduce the detail and continuous tones of a...
), and many zones were either not completed or properly published. The plates which were taken generally still exist, but cover only half of the sky. They are typically archived at their original observatories. A very few plates have recently been re-measured and re-analysed with the availability of the Hipparcos Catalogue data (see below).
Combination of the Astrographic Catalogue with Hipparcos
The vast amount of work invested in the Astrographic Catalogue, taking plates, measuring, and publishing, looked for a long time as giving only a marginal scientific profit. But today, astronomers are very much indebted to this great effort because of the possibility of combining these century-old star positions with the results from ESA's HipparcosHipparcos
Hipparcos was a scientific mission of the European Space Agency , launched in 1989 and operated between 1989 and 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial objects on the sky...
space astrometry satellite, allowing high accuracy proper motions to be derived for 2.5 million stars. Specifically, the Astrographic Catalogue positions were transferred from the decades-old printed catalogues into machine readable form (undertaken at the Sternberg Astronomical Institute
Sternberg Astronomical Institute
The Sternberg Astronomical Institute , also known as GAISh , is a research institution in Moscow, Russia, a division of Moscow State University. The institute is named after astronomer Pavel Karlovich Shternberg.The asteroid 14789 GAISH was named in its honour.-External links:*...
in Moscow under the leadership of A. Kuzmin) between 1987–94. The data were then reduced anew (at the US Naval Observatory in Washington under the leadership of Sean Urban), using the reference stars measured by the Hipparcos
Hipparcos
Hipparcos was a scientific mission of the European Space Agency , launched in 1989 and operated between 1989 and 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial objects on the sky...
astrometry satellite. The 120,000 highest accuracy stars from the Hipparcos Catalogue were used to establish a detailed reference framework at the various epochs of the Astrographic Catalogue plates, while the 2.5 million stars in the Tycho-2 Catalogue provided a dense reference framework to allow the plate distortions to be accurately calibrated and corrected. The proper motions of all the Tycho Catalogue stars could then be derived especially thanks to the Astrographic Catalogue, but additionally using star positions from more than 140 other ground-based catalogues. Aside from the 120,000 stars of the Hipparcos Catalogue itself, the resulting Tycho-2 Catalogue (compiled at the Copenhagen University Observatory
Copenhagen University Observatory
Københavns Universitet Astronomisk Observatorium on Østervold is an astronomical observatory owned and operated by Copenhagen University . It is located in Copenhagen, Denmark, and has been in operation since 1861. It has IAU code 035.*Alt 10 m asl-External links:**...
under the leadership of Erik Høg) is now the largest, most accurate and most complete, star catalogue of the brightest stars on the sky. It is currently the basis for deriving positions for all fainter stars on the sky. Sean Urban of the US Naval Observatory wrote in 1998:
The history of the Astrographic Catalogue endeavour is one of dedicated individuals devoting tedious decades of their careers to a single goal. Some believe it is also the story of how the best European observatories of the 19th century lost their leadership in astronomical research by committing so many resources to this one undertaking. Long portrayed as an object lesson in overambition, the Astrographic Catalogue has more recently turned into a lesson in the way that old data can find new uses.
Other Links
- Henry Chamberlain RussellHenry Chamberlain RussellHenry Chamberlain Russell, CMG, FRS, was an Australian astronomer and meteorologist.-Early life:Russell was born at West Maitland, New South Wales, the fourth son of the Hon. Bourn Russell and his wife Jane, née Mackreth...
for further details of the Australian contribution - http://www.to.astro.it/astrometry/AC_CdC/ IAU Commission 8 Working Group, includes a photograph of nuns measuring the Vatican plate collection (1910–1921)
- http://www.imcce.fr/fr/ephemerides/astronomie/Promenade/pages5/549.html Histoire de l'Observatoire de Toulouse (with a section on the Carte du Ciel)
- http://www.astropa.unipa.it/Library/CarteduCiel/index.htm A compilation of historical material by the Torino Observatory