The participation of Mexican astronomers in international projects dates back to the eighteenth century, when they observed the 1769 transit of Venus. More than a century later, they again participated in attempts to establish a precise value for the astronomical unit through the transits of Venus that occurred in 1874 and 1882. In 1887 Mexican astronomers were invited to join efforts to develop a multinational initiative known as the Carte du Ciel and International Astrographic Project, collaborating with 17 other observatories worldwide. Mexican astronomers obtained support from their Government, and they ordered telescopes from the Irish firm of Sir Howard Grubb and Company. An astrograph was used to photograph stars in Mexico's assigned sky zone (between declinations -10 degrees and -16 degrees) down to a limiting magnitude of 11 for the Astrographic Catalogue, and down to magnitude 14 for the Carte du Ciel. The Astrographic Catalogue photography began in February 1900, and the first of the plates for the Carte du Ciel was exposed in 1905. The Mexican astronomers had to overcome a number of serious difficulties, such as the Mexican Revolution of 1910-1920, which caused several delays and the loss of many personnel from the National Astronomical Observatory of Mexico, and then World War I, 1914-1918, which hindered the arrival of the photographic plates and interrupted communication with the Carte du Ciel Commission in Paris. Women usually were employed as 'computers' to measure the Astrographic Catalogue star positions. Between 1921 and 1962, seven volumes were published listing Mexican Astrographic Catalogue star positions. Mexican astronomers finished taking all of the Carte du Ciel plates, except for the -12 degrees declination zone, but because of financial constraints only 375 plates were printed. Afterwards, from 1941, photography of the -13 degrees zone was repeated in order to obtain stellar positions for proper motion studies. In March 1970 the mounting of the historic 33-cm Grubb astrograph and accompanying 25.4-cm guidescope was used at Miahuatlan, Oaxaca, together with a replacement tube assembly and objective to observe a total solar eclipse. Then from 1976 to 1979 three Astronomy students from the National University of Mexico reconstructed and renovated the original Grubb twin-telescope, which is now at Tonantzintla, near Puebla, and is used mainly for educational purposes.
