Astronomy offers a unique opportunity for promoting the science teaching in its present crisis. Astronomy can be introduced at various levels and become the medium by which both primary science education and public understanding of science are stimulated.

At the University level, astronomy can be introduced in the curricula of university colleges and be a subject for M.Sc. and Ph.D. degrees. Astronomy, can give students the opportunity to work scientifically from observations and known physical laws in order to derive knowledge in another field of science. Astronomy can be taught with less formalism and more experimentation, giving students a feel for the link between a phenomenon and its theoretical representation, and how and why a given observation can be represented by different theoretical models.

The International Celestial Reference Frame (ICRF) is realized by the positions of 608 compact extragalactic radio sources (Ma & Feissel 1997) with milliarcsecond (mas) and sub-mas accuracy, all being on the same system, the International Celestial Reference System (ICRS). The Hipparcos Catalogue (ESA 1997) is the practical realization of the ICRF at optical wavelengths, giving accurate positions (≈ 1 mas) at the mean epoch of 1991.25 and proper motions (≈ 1 mas/yr) for 117995 stars. This is about 2.5 stars per square degree, most being in the 7 to 9 magnitude range and a few as faint as 12. However, for many astronomical applications the Hipparcos Catalogue is not dense enough and does not reach faint enough magnitudes.

The Tycho Catalogue (ESA 1997) provides accurate positions (≈ 25 mas) for about one million stars to magnitude 11, but lacks precise proper motions. Ground-based observations are an efficient way to complement the Hipparcos mission and to extend the optical reference frame to fainter magnitudes and yield a denser grid of astrometric standard stars. New reductions of early epoch photographic data will be used to provide highly accurate proper motions for stars to about magnitude 12. Current and new observational projects will extend the optical reference frame to even fainter magnitudes.

At its 23rd General Assembly, Kyoto 1997, the IAU decided that the International Celestial Reference Frame (ICRF) should be defined by the positions of 608 compact extragalactic radio sources (Ma & Feissel 1997), with the Hipparcos Catalogue (ESA 1997) being its practical realization at optical wavelengths. Although the Hipparcos instrument was unable to observe the defining sources of the ICRF directly in the optical regime, it is linked to the ICRF via a number of auxiliary observations (Kovalevsky et al. 1997). The Hipparcos Catalogue is the first celestial reference frame which is constructed from observations not made from the surface of the Earth.

In the Soviet Union (SU) professional curricula were the same in each republic. After the dissolution of the SU the various states in the Commonwealth of Independent States gradually adopted quite different curricula. Some professions were narrowed in scope or were no longer provided for. Until recently there were, in Central Asia, three types of curricula for taining astronomers.

Similarly to other developing nations, Mexico is a country full of contrasts and contradictions; within the country there are many very backward conditions, and yet it strives to participate in advanced scientific activities.

The country has 95 million inhabitants, the median age of the population is 18 years, the fraction of teenagers that attend upper high school is 30% and the fraction of those in the 18-22 age bracket that attend college is 14%. Finally it should be pointed out that the expenditure in science amounts to 0.3% of the Gross National Product, GNP. These figures should be compared with developed countries, where 85 % of the youngsters attend high school, 45 % of those in the 18-22 age bracket attend college, and typically 1 % of the GNP is spent on science.

In compliance with the 1991 IAU resolutions on reference frames, the merged Hipparcos Catalogue had to be aligned in such a way that it represents at optical wavelengths the International Celestial Reference System (ICRS). This was realized as a combination of particular solutions obtained from observations of radio stars by radio interferometry, observation of quasars relative to Hipparcos stars, photographic plates including galaxies and Hipparcos stars, star catalogues referred to extragalactic objects, HST observations, and comparison of Earth orientation parameters obtained by VLBI and ground-based optical observations reduced with Hipparcos positions and proper motions. The individual results generally agree within 10 mas in orientation at epoch and 1 mas/yr in spin of the system. Two methods were used to combine the results and yielded uncertainties of 0.6 mas in orientation and 0.25 mas/yr in spin.

The latest JPL planetary and lunar ephemerides, DE405, are referenced to the International Celestial Reference Frame (ICRF) with an accuracy that approaches 1 mas for the four innermost planets, the sun, and the moon. This has been accomplished mainly by 18 VLBI observations of the Magellan Spacecraft in orbit around Venus. The ephemeris of Jupiter, however, is not well-determined since the various observations are not consistent within each other. The outer four planets continue to rely almost entirely upon optical observations; their ephemeris uncertainties lie in the 100-200 mas range.

In the following article we present the way in which professional astronomers are trying to influence the general understanding of astronomy in Mexico. The long-term goal is to have a population that includes science as part of its culture. The paper is mainly a list of some of the many things that can be done to enhance understanding of science, descriptions of the different items can be found in the references, which include the proceedings of three meetings on astronomy education and magazines dedicated to the teaching of astronomy.

The ambiguity in this paper’s title is deliberate. Are we talking about astronomers or telescopes in developing countries? And are the countries concerned developing economically or astronomically? In practice I will cover both options in each case.

The list below summarizes six possible routes for the acquisition of astronomical observational data that may be available to astronomers in countries developing economically, astronomically or in both ways. Not all these options will be available in any one case; indeed most of them will probably not be available. However, examples of all of them can readily be found.

The Hipparcos optical reference frame is compared to the basic FK5 in order to determine the orientation at T0 = 1991.25 and the global spin between the two frames. The components of the spin are significant and suggest a correction the IAU76 value of the precession constant and to a possible non-precessional motion of the equinox of the FK5. The regional errors are analysed with harmonic functions and found to be as large as 150 mas in position and 3 mas/yr in proper motion.

Extragalactic radio sources are assumed to be very distant and thus should exhibit little or no detectable proper motions. A reference frame defined by the positions of extragalactic radio sources may be said to be a quasi-inertial frame (i.e. a frame whose basis is inertial) with little or no time dependency. Unfortunately, although extragalactic sources are good as ICRF objects, most extragalactic sources display intrinsic structure on angular scales larger than the accuracy of their position estimates. Temporal variations of the intrinsic structure of these objects will result in apparent motion when observations are made at several epochs. Because the underlying physics of extragalactic sources is not as well understood as that of the stars which define the stellar reference frame, we can only describe with certainty what the radio sources did during the particular interval of time covered by previous observations. We cannot predict theoretically what behavior can be expected in the future. It is therefore necessary to regularly measure the structure of ICRF sources, and monitor their changes, in order to maintain the ICRF and make it more useful to astronomers.

There is no question that relatively small telescopes are powerful tools for astronomy, just as they always have been. With the new detectors and full usage of computers, they have become even more powerful, enabling us to do with a one-meter aperture telescope today more than 4-meter or 5-meter telescopes could do only a few decades ago. And the small ones cost a lot less to build and operate than the large ones. As such, small telescopes are the main hope for observing time for the many astronomers worldwide who need them as part of their research (or educational) tools. They can make a major impact on many areas of research and will be of great value for scientific education as well. Astronomy is very interesting to students and to the general public, not just to astronomers. Furthermore, most areas of astronomical research are data poor and more telescopes are needed to effectively attack the problems. Only a very few of us have adequate telescope time for our research or educational needs.

As discussed in other papers in this volume, the IAU XXIII General Assembly adopted a new fundamental celestial reference frame: the International Celestial Reference Frame (ICRF) based on VLBI observations of extragalactic radio sources (Ma et al., 1997). It is approximately 300 times more accurate than its predecessor, the FK5. At present, no other technique has produced a more accurate celestial frame than VLBI, Since no other astrometric technique provides an external standard of accuracy, the VLBI claim of a great leap forward in accuracy must be verified by internal consistency tests. This paper addresses one aspect of internal consistency: the ability of independent VLBI software packages to reproduce a celestial frame without significant loss of accuracy. This is no small task since the software packages are large - involving on the order of 100 000 lines of code. What does VLBI software do? Aside from routines designed to collect the data and extract raw observables which will not be considered here, its principal task is to model the differential group delay and phase delay rate of radio signals received at two widely separated antennas (Sovers, Fanselow & Jacobs, 1998). The software then refines this model via a least squares adjustment of relevant physical parameters which describe station locations, source positions, clock offsets, atmospheric refraction, tidal effects, etc. In the early 1990s, studies revealed that differences in software implementation and analyst’s choices of model options were one of the largest contributors to differences in independent calculations of VLBI celestial frames. These differences were of comparable size to the formal uncertainties of the celestial frame’s source positions.

Although the importance of astronomy as a field of basic science and a discipline of fundamental education is well recognized among us, it is not always easy to share this recognition with those people whose interests are tightly bound to their daily lives on the Earth, even within one country. The activities of the Japanese within the “Neighborhood Program” are reviewed and brief discussions of them are presented.

The International Celestial Reference Frame (ICRF) is presently realized by the positions of 608 compact, extragalactic radio sources (Ma & Feissel 1997) with milliarcsecond (mas) and sub-mas accuracy, all being on the same system, the International Celestial Reference System (ICRS). The Hipparcos Catalogue (ESA 1997) is the practical realization of the ICRF at optical wavelengths, giving high accuracy positions (≈1 mas) and proper motions (≈1 mas/yr) for 117955 stars (ESA 1997). The link between the radio and optical frames has been achieved by various methods (Kovalevsky et al. 1997). The accuracy of this link is estimated to be 0.6 mas at the mean epoch of Hipparcos (1991.25) for the orientation, and 0.25 mas/year for the system rotation.

We want to help scientists in developing countries (DC) do research because of their intelligence and devotion to science. But frankly, observational and even theoretical research is very expensive. For a developed country an estimate of the average project cost that includes salaries, the equipment used, and the institutional overhead is roughly $100,000 (US). In DC the salaries are lower, but not necessarily the equipment.

There are several international organizations currently working towards raising the standard of science and technology in the third world countries (TWCs). It is being appreciated that instead of dealing with the issue on a country by country basis, it helps to view and solve the problem in a network mode. It is sometimes the case that one TWC may have resource persons, or facilities which can benefit by sharing with the other TWCs. Or, a group of workers from different TWCs can be brought together for a school or workshop in which experts drawn from different parts of the world participate as lecturers or guides.

Heretofore, double and multiple stars have presented a tolerable but manageable problem in most astrometric programs. However, the drive to ever greater precision, with detections in the milli-to-micro arcsecond range of these complex objects, over a wide range of wavelengths, presents new and as yet unsolved problems in both the astrometry and photometry of such systems.

This discussion is aimed at a better delineation of the implications of the problem.

Before going to the central theme it is perhaps necessary to say what science is, as opposed to other human knowledge. In a rather short statement science may be defined as a world picture, or it may be closer to the heart of the matter if it is said that science is the product of organized fantasy about the real world. Up to this point it must be hastily added that there are also many other branches in human knowledge that share the same characteristics with science. For example, experiment is thought to be peculiar to science. Actually the alchemists of the middle ages did undertake experiments. What was missing in their experiments -and only later applied by Lavoisier and other giants of science in that period- are the hypothetical-deduction methods that science multiplied. Again, observations and logic were also thought to be peculiar to science. We learned, however, the astrologers did make observations and that theologians had logic and that logic is is perhaps the most methodological component of all human inquiry. Thus, as such, one would not be able to discern science from the rest of human activities. But there are boundaries within which science can legitimately operate. The first one is that science denies two types of truth: truth by logic and truth by faith. On the other hand science accommodates only one truth. The other boundary is the constant test by internal logic of necessity and by external public record. These boundary conditions must always be observed, as otherwise one will fall into the realm of magic.

In this paper we briefly describe the influence of astrometric binaries on derived proper motions and we draw some conclusions with respect to the reference systems. For more details the reader is referred to Wielen (1997) and Wielen et al. (1997).

Increased measurement accuracy determines not only the derived parameters with much more precision, but it may even allow one to describe new phenomena, which were of no importance before. This happened in the case of the highly precise Hipparcos measurements (ESA, 1997) which were able to determine stellar proper motions within less than four years with an accuracy comparable with the best proper motions available from ground-based observations as given in the FK5 (Fricke et al. 1988). The basic difference between the Hipparcos and the FK5 proper motions showed up within our task of validating the Hipparcos proper motions during the reduction process. Our main result was that the dispersion of the residual differences between both proper motions was about three times as large compared with the error estimates expected from the data given in the catalogues. Since it was rather unlikely that one of the two catalogues had so strongly underestimated its errors, we looked for other reasons to explain the discrepancy. For many of the stars with the largest differences between the Hipparcos and FK5 proper motions, information on their duplicity was found in the literature. We thus suspected that the influence of astrometric binaries to be responsible for the discrepancy.