The publication of the second Gaia catalogue is an appropriate moment to review the history of astrometry, as it was done at the Paris Observatory. Click on the various tabs how the instruments and results of astrometry has evolved.
Picard’s sector
This 38 inch (103 cm) radius sector was invented by the abbot Picard. It was the first instrument to be equipped with a sighting telescope and an adjustable wire micrometer.
The Pleiades seen by La Hire, 1693
Observation made at the Royal Observatory of the transit of the Moon over the Pléiades, March 12th 1693. La Hire a created a map o f the cluster including 64 stars.
++++The 18th century
The six foot sextant, 1750
This six foot (194cm) sextant, made by Langlois in 1750, was used by abbot La Caille to map the southern sky from 1751 to 1752.
La Caille’s map of the southern sky, 1752
Map of the southern sky, with the new constellations invented by abbot La Caille, following two years of observations at the Cape of Good Hope.
Catalogue of stars in the southern sky, 1752
Abbot La Caille, in spite of isolation and the difficult conditions, measured the positions of 10 000 stars in the southern sky, and reduced the 1942 observations to make a preliminary catalogue which survived as a standard reference for a century.
J. Bird’s mural quandrant, 1774
Lalande and his students used this large 2.45m radius quadrant for a huge observational program involving stars down to the 11th magnitude.
Observations made at the Ecole Militaire, 1790
It was mainly Lalande’s nephew, Michel Delalande, who made the 1790 measurements for the very ambitious 50 000 star catalogue.
Catalogue of 50 000 stars, 1801
After 11 years of work, the observations of 50 000 stars were published by Lalande. However, this monumental work is virtually unusable, since the observations have not been reduced.
++++The Carte du Ciel photographique
The Pleiades photographed by the Henry brothers, 1885
This map is the fruit of the first photograph of the cluster usable for astrometric purposes. It was used to count 1421 stars down to the 16th magnitude.
The Carte du Ciel equatorial
Prototype built by Gautier in 1885 of almost all the equatorials used for the worldwide Carte du Ciel enterprise.
Negative of a photograph of the Pleiades, 1906
This negative, from the Carte Photographique du Ciel collection, shows 2340 stars. One can distinguish the nebulosities surrounding the stars Maïa and Mérope.
Measurement of the Carte du Ciel plates in 1890
In 1890, women are enrolled for these measurements. This had two advantages, in tune with the spirit of the time: lower salaries coupled to the care associated with women!
++++19th - 20th centuries
Hall of the meridian instruments at the Paris Observatory
This hall houses three instruments: a large Secrétan-Eichans meridian, a Gambey meridian refractor and a Gambey mural circle.
Catalogue of the des Astronomischen Gesellschaft 1890-1902
This catalogue (AGK) was destined to cover the northern hemisphere with a network of 150 000 stars. 13 observatories, including that of Paris, participated in this international enterprise.
Bischhoffshein’s meridian instrument in its original state (1877)
This so-called « garden » meridian instrument is a generous gift by the Bischofschein banker who donated it to the Paris Observatory during Le Verrier’s era. It was used to observe again the stars in Lalande’s 50000 stellar catalogue, and subsequently in various international programs including that of the latest AGK3 catalogue.
Danjon’s impersonal astrolabe, 1951
André Danjon perfected the prism astrolabe, thus reducing considerably the measurement.
++++20th - 21th centuries
Hipparcos, the first astrometric satellite
The satellite was launched on the 8th of August 1989 and, in spite of a defective orbit, it has observed the 118 000 stars foreseen in its program up to March 1993. The accuracy of its measurement of distances and proper motions in the sky has l to a considerable research effort on the physics of stars and on the Galaxy.
The Pleiades in the Millenium Star Atlas
A map created by Hipparcos, the first astrometric satellite, with observations covering the years 1989 to 1993; one obtained the distances of the closest, and the dimmer stars than those known till then.
The Paris Observatory Gaia team on the day of the launch
The satellite was launched on December 19th 2013 and reached its working orbit around the Lagrange 2 point. It really began to operate on August 24th 2014. And its
Artist view of Gaia satellite
crédits : ESA/ATG medialab; background: ESO/S. Brunier