Journal of Astronomical History and Heritage, 23(3), 601–613 (2020).

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THE MEXICAN ASTROGRAPHIC CATALOGUE AND CARTE DU CIEL PROJECT

Marco Arturo Moreno Corral and William J. Schuster

Instituto de Astronomía, Campus Ensenada, Universidad Nacional Autónoma de México, Ensenada, 22860, Baja California, México.

Emails: mam@astro.unam.mx, schuster@astro.unam.mx Abstract: 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° and –16°) 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° declination zone, but because of financial constraints only 375 plates were printed. Afterwards, from 1941, photography of the –13° 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 Miahuatlán, 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.

Keywords: Carte du Ciel, Astrographic Catalogue, astrometry, photographic astronomy, Grubb astrograph, Angel Anguiano, Joaquín Gallo, Guillermo Haro, Felipe Valle 1 INTRODUCTION

During the eighteenth and nineteenth centuries one of the most important challenges faced by astronomers was to determine the Earth-Sun distance (the ‘astronomical unit’, henceforth a.u.), and much has been written on this topic (e.g. see the references listed in Sheehan and Westfall, 2004). Astronomers in the eighteenth century made epic efforts to obtain the obser-vational data necessary to solve this problem (Woolf, 1959), in many cases making long and difficult ocean voyages (e.g., see Orchiston, 2017), that in some cases even cost them their lives.

The participation of Mexicans in important international astronomical projects began in 1769 when Joaquín Velázquez de León, Anton-io Alzate and Ignacio Bartolache observed the 3 June transit of Venus (Engstrand, 1976). The first of these astronomers observed the entire transit from a temporary camp that he estab-lished in the southern part of the Baja California Peninsula (see Figure 1 for Mexican localities mentioned in the text), while the other two ast-ronomers were based in Mexico City (see Figure 2) and could only view part of that event

(Moreno Corral, 2013; Moreno Corral and de Lara Andrade, 2013; Westfall, 1992). Their data were sent to France, where Cassini pub-lished them along with those of other observers, in order to determine the solar parallax.

Another transit of Venus occurred 105 years later, on 9 December 1874, and on that occasion it would only be visible from parts of the Pacific Ocean and in some regions of Southeast Asia. Seeking to contribute to the accurate measurement of the a.u., the Govern-ment of Mexico organized the Mexican Astro-nomical Commission, comprising five members (Figure 3) who, after a challenging journey, arrived in Japan, which at that time was be-ginning to open up to the Western world. There they found that a group of French astronomers (Débarbat and Launay, 2006) and an American expedition (Dick et al., 1998) had already settled in Nagasaki. As soon as he landed on Japanese soil, the head of the Mexican dele-gation, Francisco Díaz Covarrubias (1833–1889; 1876) initiated procedures to allow the Mexicans to establish two observatories. After approval was granted by the Japanese author-ities, one observing site was established in the

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Figure 1: Mexican localities mentioned in the text (map: Wayne Orchiston). north-western part of Yokohama Bay (known as Nogue-no-yama) and the other nearby, on Bluff Hill (see Figure 4). Diaz Covarrubias (1876) contacted other groups of visiting foreign ast-ronomers and, in combination, they made mea-surements to establish the positions of the sites from which they would observe. After installing the telescopes and other instruments and test-ing their correct operation, the day of the transit arrived. The two groups of Mexicans had excel-lent weather conditions and were able to suc-cessfully observe the transit. Their results were published months later in Paris (Díaz Covar-rubias, 1875). 2 THE FOUNDING OF THE NATIONAL ASTRONOMICAL OBSERVATORY OF MEXICO

Thanks in part to the success of the Japanese trip and the experience and international con-tacts that the Mexicans achieved by participat-ing in those observations, but also because of the need felt by Mexico to have an institution where astronomy would help various geodes-ic, topographic and cartographic projects that were occurring throughout the country, in 1876 the engineer Angel Anguiano (1840–1921) was commissioned to develop a project aimed at creating a center that would serve these pur-poses.

After adapting Chapultepec Castle, located in the northwestern sector of Mexico City and installing in it various instruments (such as meridian circles, zenith tubes, chronometers and magnetometers), the National Astronomi-

cal Observatory of Mexico (henceforth OAN-M) was founded on 5 May 1878 and Anguiano (1880) was appointed the inaugural Director. The first scientific work that was carried out there was the observation of the 6 May 1878 transit of Mercury. Due to the proximity of this planet to the Sun and its angular size as seen from the Earth, these transits could not be used to determine the solar parallax (and hence the a.u.), but this particular transit was used by the Mexicans to test their equipment, and above all to train students in preparation for the upcoming 1882 transit of Venus (Jiménez, 1878). 3 THE 1882 TRANSIT OF VENUS

Only four years after the founding of the OAN-M, the second nineteenth century transit of Venus would take place. That event would occur on 6 December 1882, and would be observable in its entirety from Mexican territory. For this reason, in 1878 staff at the OAN-M began arrangements to participate in its study. They obtained a significant amount of money from the Government so that they could acquire the telescopes and other instruments needed to carry out these observations. For this reason, Anguiano (1882) traveled to Europe in 1880 to buy this equipment, in the process taking the opportunity to visit some of the most important observatories in that continent and establish contact with European astronomers. Although he acquired telescopes and equipment from dif-ferent manufacturers, including a Dallmeyer photoheliograph similar to one that had been used successfully in the 1874 transit observat-

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Figure 2: An engraving depicting the observation of the transit of Venus of 1769, made from Mexico City by Antonio Alzate and Ignacio Bartolache (digital image courtesy: the Public Library of Toledo, Spain).

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Figure 3: Mexican astronomers who traveled to Japan in 1874 to observe the transit of Venus of that year. In the background and from left to right are Francisco Jiménez, Francisco Díaz Covarrubias and Francisco Bulnes. Seated and in the same order are Agustín Barroso and Manuel Fernández Leal (courtesy: Historical Archive of the Astronomy Institute at the National Autonomous University of Mexico (UNAM), Mexico City). ions made at Melbourne Observatory in Aust-ralia (see Clark and Orchiston, 2004), Anguiano was particularly keen that Howard Grubb and Company of Dublin, Ireland (Glass, 1997; Orchiston 2010) should construct two refractors

for the Mexican observatory, which would be used to study this transit. Due to the contacts that he established during that trip, in 1882 a party of French astronomers arrived in Mexico headed by Jean Jacques Anatole Bouquet de la Grye, who, based upon weather reports and other information that the Mexican astronomers had gathered from different locations of the country, decided to set up his scientific camp outside the city of Puebla (Bouquet de la Grye, 1905), one of the main regional capitals of Mexico at that time. In addition to achieving good observational results, members of the French expedition interacted with their Mexican colleagues, establishing contacts that were decisive for Mexico’s subsequent participation in an ambitious international project aimed at producing a large photographic atlas of the sky and an accompanying catalogue of star posit-ions. 4 THE INVITATION

In May of 1887, Teodoro Quintana, one of the Mexican astronomers interested in using photo-graphic techniques, took photographs of the Moon that showed great detail, which prompted Anguiano to send them to de la Grye, who was on the staff of Paris Observatory. Indeed, those photographs were remarkable, so the French astronomer showed them to the Director of that institution, Rear-Admiral Ernest Amédée Bar-thélemy Mouchez, who for several years had been promoting the development of astronom-ical cartography, which

Figure 4: The two Mexican observing stations at Yokohama, one at Nogue-no-yama (left) and the other at Bluff Hill (right) (courtesy: www.transitofvenus.nl/history.html).

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… recorded the general state of the sky at that time and obtained information that would make it possible to determine the positions and sizes of all stars up to ade-quate order of magnitude. (Lamy, 2009a: 195),

for which he convened an International Astro-photographic Congress that was held in Paris in April, 1887. This was attended by 58 astron-omers representing 16 countries. There, the main objective was to produce a Carte du Ciel (henceforth CdC) consisting of celestial charts containing images of all stars down to photo-graphic magnitude 14. Secondly, they agreed to produce a printed Astrographic Catalogue (AC), containing accurate coordinates for all stars down to magnitude 11 (Débarbat et al., 1988; Turner, 1912). Lamy (2009b: 119) has described the CdC:

… by employing recent developments in photography, the Carte du Ciel combined at the end of the nineteenth century a tradit-ional astronomical theme (inventory of the sky) and a recent technology (photo-graphy). The Carte du Ciel required co-operation on a world scale. It was founded on the definition of common rules for all the astronomers.1

On the basis of the lunar photographs tak-en by the Mexicans, Mouchez decided to invite the OAN-M to be one of the eighteen partici-pating observatories, distributed across the planet, that would perform the work of this ambitious observational project (León, 1911). Evaluating the project and considering the tech-nical, material, and personnel needs required to carry it out, the Mexican astronomers submitted to the Government of Mexico a request to ac-cept that invitation and to grant the financial resources necessary to acquire the astrograph and auxiliary equipment. These requests were approved, so Anguiano (1888) formalized the Mexican participation, and was in charge of investigating the technical aspects necessary to make the purchase of the astrograph. 5 THE TWIN-TELESCOPE ACQUIRED BY MEXICO

Those who attended the Congress voted on a set of mandatory resolutions for all the partici-pating observatories, among which there were some concerning the types and characteristics of the telescopes used. It was agreed that

The instruments used will be exclusively refractors. The lens aperture will be 0.m33, and the focal length will be 3-m 43-cm, so that one minute of arc is precisely re-presented by 0.m001. The objectives will be constructed so that the usable field is at least 1º from the center. The tubes of the

photographic instruments will be construct-ed with the most favorable metal to obtain an invariable focal plane and will have a graduation that allows determining and fix-ing the position of the plates. (Grubb …, 1926: 6–7).

With this information Anguiano had to de-cide who would make the Mexican telescope. At first he thought of ordering it from the Gautier Company in Paris, which employed the broth-ers Paul and Mathieu Prosper Henry, important telescope-builders at that time, who were the ones who built the prototype that defined the characteristics of those telescopes that would be used for the CdC Project. But as the company in charge of manufacturing the tele-scopes for several of the participating observa-tories, the delivery time for Mexico would be at least two and a half years. So Anguiano accepted the proposal of the Grubb company, which offered to produce the twin-telescope in one year. In addition, the OAN-M also had two refractors built by that same manufacturer: one with a primary lens 15 inches (38-cm) in dia-meter and the other with a 6-inch (15-cm) ob-jective, which fulfilled the expectations of the Mexican astronomers. So, in 1888 a contract was signed with the Grubb company, which, although responsible for manufacturing the 13-inch (33-cm) astrographs and paired 10-inch (25.4-cm) guidescopes for the observatories at Greenwich, Oxford, Melbourne, Cork, Perth, and Cape Town (Grubb …, 1926: 43), offered to deliver the Mexican instrument in just one year.

The Mexican astrograph and guidescope were finished on time (see Figure 5) and sent to Mexico City, arriving in 1890. At the end of that year the instrument was installed in a dome built expressly for this project in the new build-ing of the OAN-M in the town of Tacubaya, a small settlement about eight kilometers from Mexico City. Figure 6 shows the twin-telescope in its new dome; note that for convenience the astrograph and the guidescope had objectives with identical focal lengths, namely 3.43 metres. As soon as the instrument was operational the Mexicans began photographing the sky, first to acquire the necessary practice, both in the use of the twin-telescope and in the techniques necessary for successfully photographing the zone of the sky assigned to them. This was between –10° and –16° declination, an area with only one star of the first magnitude, Spica (α Vir), even though it contained part of the Milky Way. 6 TESTS AND FIRST RESULTS

In 1891, regular work began at the Observatory to obtain the plates needed to completely cover the area of the sky assigned to the Mexicans by

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Figure 5: The Mexican Carte du Ciel twin-telescope undergoing final tests at the Grubb factory in Dublin (courtesy: Historical Archive of the Astronomy Institute, UNAM). by the International Congress. Each plate mea-sured 13 × 13 cm, and as each millimeter cor-responded to a minute of arc, covered more than two square degrees of the celestial sphere. The plates used by the Mexican ast-ronomers were of the Lumiere, Seed and Elliot brands, and the way in which they proceeded to minimize the defects in the emulsions of these, was to take a first exposure of six min-utes, then slightly shift the telescope, and an-other of three minutes, and then finally one more—also displaced by twenty seconds of arc. In such a way, the resulting stellar images appeared on the plates in the form of equilateral triangles, with each of its vertices occupied by an image of different intensity of the same star. After this and before developing the plate, they proceeded to produce by contact and by means of a luminous flash, a rectangular grid divided into rectangles of five centimeters (this grid was referred to as a ‘reseau’). When each plate was finally developed, in addition to the triangularly distributed stars, a grid was also printed on the negative that would serve as a rectangular coordinate system for all the stars present on the same plate, and which would later facilitate determining their coordinates with respect the reference stars present in each field.

Obtaining the plates for the AC actually be-gan in 1892, but from the beginning the Mexi-

can astronomers realized that there were some effects that produced deformed stellar images. After several attempts to solve this problem, in 1897 they sent some plates to Paris, where it was confirmed that there were problems and that these had to do with the assembly of the two lenses that formed the astrograph object-ive. Because of the difficulty in sending the objective to Grubb in Dublin, staff at the OAN-M decided to take the objective to Alvan Clark & Sons in Cambridge, Massachusetts (Valle, 1902), which already had a great reputation as a lens-builder for large telescopes (Warner and Ariail, 1996). There the necessary tests and corrections were carried out, after which Lieu-tenant Colonel Teodoro Quintana brought the lens back to Mexico in 1899. In the process, he took great care, and during the return journey of more than 4500 km by rail, he never once was separated from the box that contained the astrograph optics.2 7 THE REAL PHOTOGRAPHIC WORK

As soon as it arrived in the Mexican capital, the lens was reinstalled in the Grubb astrograph and after careful tests, everything was found to be fine, so by February 1900 the astrograph was ready to begin photographing its sky zone. A year later, the engineer Felipe Valle, who was then the Director of the Observatory, informed

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Figure 6: The same telescope in its dome at the National Astronomical Observatory of Mexico at Tacubaya, in 1890 (courtesy: Historical Archive of the Astronomy Institute, UNAM). .the members of the Permanent Committee of the Carte du Ciel that 540 plates had already been taken (of the 1260 plates needed to completely cover their assigned sky zone), and that 135 of these were fully measured, which meant that by then the Mexicans had determin-ed forty thousand precise star positions.

From this date, everything seemed to go well for the photographic work, despite the rainy months typical of Mexico City, and in six years the OAN-M had managed to take the necessary plates to cover their entire Mexican AC zone. Then from 1905 onwards, some of the plates required for the CdC project were obtained. These required longer exposures and the best possible atmospheric conditions (Gallo, 1928).

One of the Mexican astronomers who de-voted much of his time to obtaining the CdC plates was Joaquín Gallo (1928: 8), and elab-orated on this:

… the same celestial centers that served for the Catalog, served for the Chart of the Sky, but with more time of exposure so that stars of magnitude 14th appeared in the plates, which demanded more time of ex-posure and a perfect atmospheric state; several times it happened that in the middle of the exposure of a plate the sky would be covered or cloudy, thus losing the work.

That is why over a 20-year period only about 500 plates had been published, also taking into account that during the times of the European War it was impossible to reproduce the nega-

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tives, which was normally carried out in Paris (Gallo Sarlat, 1982). 8 NEW DIFFICULTIES

While this was happening, on 20 November 1910 the Mexican Revolution erupted. This was an armed uprising that lasted for several years and impacted on all levels and activities of society. During the first years of the Revo-lution the Observatory remained reasonably aloof from the armed struggle, as it tried to con-tinue with its regular operations. Among these was the CdC Project, which played a pre-dominant role as it consumed the majority of the time, resources and personnel of the Obser-vatory. Thus, at that time all of the required plates for the CdC Project were taken to cover the sky zone between declinations –11º and –12º, where to obtain each plate three expos-ures of 20 minutes each were made. During the more violent years the Observatory had to sus- Table 1: Publication of the Mexican Astrographic Catalogue volumes.

Volume Declination Zone Year of Publication I –16º 1921 II –15º 1931 III –14º 1934, 1940 IV –13º 1942, 1943 V –12º 1944, 1945 VI –11º 1947, 1960 VII –10º 1961, 1962

pend activities, for example, during some weeks of 1913, 1914 and 1915. In addition, at that time the Observatory suffered severe reduct-ions in personnel, so that the only astronomer employed was the Director.

The situation was further complicated by the outbreak of World War I, which greatly hin-dered access to the CdC photographic plates since these were acquired from Europe. The war also caused a breakdown in regular com-munication between astronomers and mem-bers of the Permanent Committee in charge of coordinating the CdC Project, who were based in Paris. Mexican representatives had attended CdC meetings held in 1896, 1900 and 1909, but WWI brought a halt to these meetings. How-ever, when the International Astronomical Union (IAU) was created in 1919, the CdC Committee became part of it, embodying Com-mission 23. When members of the OAN-M—which at the time was the only group of pro-fessional astronomers in the Mexican nation—found out about the formation of the IAU they took the necessary measures for Mexico to join, together with Italy, the first nations that were added to the original group of seven founding countries (Blaauw, 1994). Since then, Mexico has been part of the IAU and through it has

continued to fulfill the commitment made in 1887 to participate in the AC and CdC Projects.

Despite these difficulties and the drastic reduction of personnel that the Observatory suf-fered during the 1920s and 1930s, in 1921 it began to publish the Mexican AC, and over the next 41 years eight Volumes were published, some in two parts (see Table 1). When the final volume appeared in 1962 (Zubieta, del Campo and de Gyves, 1953), the astronomers at the OAN-M had fulfilled the commitment they orig-inally made 75 years earlier (in 1887) to pro-duce a star catalogue with the equatorial co-ordinates of all stars down to the magnitude 11, contained between the declinations –10º and –16º.

As for the CdC Project, the corresponding plates began to be taken at the end of 1905, but the –12º zone was never photographed. The original plates were sent to Paris, where the printing companies of L. Shützenberger and L. Massard, using the heliogravure method, en-larged the plates to double their size and then printed them on cardboard. Due to the high costs of this procedure, only 375 plates were enlarged and reproduced in this manner (and an example is shown here in Figure 7). The celestial maps produced in this way, were distributed among the main observatories of the world, including, of course, those that partici-pated in this ambitious project.

It is important to point out that—as hap-pened in other observatories of the world (e.g. see Stevenson, 2015)—that much of the delicate and precise work of measuring the photographic plates and deriving the positions of stars for the AC was done by women, who were trained as plate measurers and to use microscopes specially designed for this de-manding work. They were the ones who calculated the equatorial coordinates of stars present on the plates. In fact

The calculation is complex, involving first calculating standard coordinates from the x and y measures, calculating plate constants and then converting to spherical coordin-ates. The difficulty in doing these calcu-lations is presumably why it took years, and sometimes decades, between publishing volumes of the catalogue. (Nick Lomb, pers. comm., September 2020).

Most of the Mexican women involved in these reductions were daughters of male staff mem-bers of the Observatory, and further research is required in order to learn about their individual contributions.

From 1941, Observatory staff began taking repeat plates of part of their original CdC zone in order to carry out proper motion studies (Zu-

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Figure 7: One of the published Mexican Carte du Ciel zones (courtesy: Institute of Astronomy, UNAM). bieta, 1985). The instrument used for this project was the original Grubb astrograph, but in the interim Mexico City had grown so much that Tacubaya—once far away from the city—was now in the suburbs and light pollution made this work very difficult. Consequently, between 1894 and 1941 the number of nights per year when successful photographs of the sky could be taken had dropped enormously, but in spite of this the whole –13º declination zone was photographed, and the proper motions of stars

in this zone were published (Zubieta, 1985). 9 CONCLUDING REMARKS

By the end of the 1940s the growth of Mexico City had engulfed the OAN-M, making astro-nomical observing impossible, which is why the Director at that time, Dr Guillermo Haro (1913–1988), made the decision to move the Grubb astrograph to the small town of Tonantzintla, lo-cated in the state of Puebla, southeast of the

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Figure 8: The dome and telescope of the Carte du Ciel in its current location in Tonantzintla, Puebla, Mexico (photograph: M.A. Moreno Corral). Mexican capital. This is where the National Astrophysical Observatory was founded, in 1942, the second institution of this type that existed in Mexico with official support. In 1951 the old Grubb astrograph was moved from Tac-ubaya to Tonantzintla and housed in a new dome (see Figure 8). Its geographical co-ordinates are now 19° 91′ 56.8′′ N and 98° 18′ 52.1′ ′ W. Figure 9 shows Dr Haro observing Figure 9: Dr. Guillermo Haro using the Carte du Ciel telescope at Tonantzintla in 1958 (courtesy: Historical Archive of the Astronomy Institute, UNAM).

with the old telescope in 1958.

On the occasion of the total solar eclipse of 7 March 1970, which was visible in much of Mexico, it was decided to install an observing camp on the outskirts of the town of Miahuatlán, in Oaxaca, where astronomers from the Instit-ute of Astronomy at the National Autonomous University of Mexico (UNAM) could study the solar corona. The Institute of Astronomy had evolved out of the ancient Tacubaya Observa-tory (which had been demolished), and they were given the old Grubb astrograph, which they decided to modify for this project (see Figure 10). The Institute’s opticians designed and built a suitable lens which was inserted in a rectangular tube that was installed on the equatorial mounting of the old twin-telescope to take advantage of its reliable clockwork drive (Little and Robinson, 1970). As a result, the old CdC twin-telescope was removed, and the new telescope with the old Grubb mounting was taken to Miahuatlán.

After that eclipse, the instrument returned to Tonantzintla but was not reassembled at the time. This situation only changed in 1976 when two Astronomy students (Marco Arturo Moreno Corral and José Peña) and one of the optical specialists (Zacarías Malacara) from that same institute, were interested in returning the hist-oric Grubb twin-telescope to its original condit-ion. As some of the clockwork brass parts and the guide micrometer had been lost, it was necessary to rebuild these, which took time. This work eventually was completed in 1979, and the old Grubb twin-telescope became oper-able again (Figure 11). The historic Grubb CdC astrograph and guidescope are still at Ton-antzintla, and since we no longer have access to photographic plates and the sky over Puebla now suffers from considerable light pollution, the old twin-telescope is used for educational purposes. In this way, groups of schoolchildren and visitors of all ages learn about historic astronomical telescopes and an interesting episode in the rich astronomical history of Mexico. 10 NOTES

1. It is important to realise that the AC and the CdC were two very different projects. Mou-chez’s intention at the 1887 meeting in Par-is was to promote the CdC (see Mouchez, 1887), but David Gill proposed that the AC be undertaken as an additional project in parallel with the CdC. Stevenson (2015: 11) reminds us that “The Carte du Ciel and Astrographic Catalogue were therefore two separate projects connected by their temporality, organisation and instrumenta-

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Figure 10: Preparation of the Carte du Ciel mount to install a telescope designed to record the solar eclipse of 7 March 1970 from Miahuatlán, Oaxaca, Mexico. The technician is José (Pepe) Alva of Tonantzintla (courtesy: Historical Archive of the Astronomy Institute, UNAM).

tion.” Both would involve photographs tak-en with ‘standardized astrographs’ located at the different participating observatories.

To provide a reference framework, the positions of selected ‘reference stars’ in the allocated sky zones typically were obtain-ed using transit telescopes or meridian circles at the participating AC-CdC obser-vatories, or sometimes at collaborating ob-servatories that otherwise were not involv-ed in these Projects. The Mexican astrono-mers used one of the meridian circles at the Observatory to make these observations (Beltrán y Puga, 1893: 15).

2. The National Astronomical Observatory of Mexico was no means the only AC-CdC observatory to encounter problems—see Lamy (2009b).

11 ACKNOWLEDGEMENTS

We are grateful to Professor Nick Lomb (Uni-versity of Southern Queensland) for reading and commenting on the original manuscript; to Professor Wayne Orchiston for helping finalise this paper; to the Public Library of Toledo (Spain) for supplying Figure 1, and to the Historical Archive at the Astronomy Institute (UNAM) for providing Figures 2, 4–6, 8 and 9. 12 REFERENCES

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Figure 11: The current state of the Mexican Carte du Ciel telescope at Tonantzintla, Puebla (photograph: M.A. Moreno Corral).

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Marco Arturo Moreno Corral was born in Mexico City in 1946. He studied physics and astrophysics at the National Autonomous University of Mexico. In 1971 he began working on the development of the

National Astronomical Obser-vatory located in the Sierra de San Pedro Mártir, Baja Cali-ifornia, Mexico. He was a Sen-ior Researcher at the Institute of Astronomy of that University until 2019 when he retired.

His fields of interest have been the formation and evo-lution of low mass stars (T Tauri

and WTT stars), the kinematics of HII regions and the structure of planetary nebulae. Between 1989 and 1990 he was coordinator of the Astrophysics Area of the National Institute of Astrophysics, Optics and Electronics located in Tonantzintla, Puebla.

He became interested in the implantation and development of exact sciences in colonial Mexico during the sixteenth to eighteenth centuries, and has published various papers and books on the subject. He also has been involved in the reconstruction and preservation of the telescopes of the old National Astronomical Observatory of Mexico, which was founded in 1878.

William J. Schuster was born in Elkhart, Indiana, USA, in 1948, and received a BS in Astronomy from Case Western Reserve University (tau beta pi, 1976), and a PhD from the University of Arizona (phi beta kappa, 1976). The photometric observations for his doctoral dissertation were made at the

Mexican National Observatory, San Pedro Mártir, Baja California, where he continues to work to this day. Since 1974 he has been a researcher at the Astronomy Institute, UNAM (México).

His main observational projects have concerned stellar photometry and spectroscopy of Galactic halo and thick-disk stars, as well as photometry of subdwarf and solar-type stars, standard stars, atmospheric extinction, Galactic open clusters, and asteroids. William has gained expertise within three photometric systems: 13-colors of Johnson-Michell, uvby-β of Strömgren-Crawford, and UBVRI of Johnson-Kron-Cousins. He has published more than 75 research papers in international journals, which have garnered more than 2300 citations. William has supervised 5 Bachelor theses, 4 Masters, and 2 PhDs, participated in numerous Observatory sum-mer schools and outreach events, taken data at observatories in Mexico, Chile, the Canary Islands, and USA, and collaborated with astronomers from Denmark, Italy, Mexico, Portugal, Spain, Turkey and the USA.

Apart from Astronomy, William loves photo-graphy, jazz music, reading novels, hiking, and basketball, and specially his two children, Pilar Citlali and Daniel William.