Early developments

In the 1920s there were further initiatives to improve considerably the status of observational astronomy in our country. Two motives constantly recur: to procure an up-to-date instrumental installation and to utilise the more favourable climatic conditions of the south. In these schemes, which first emanated from the observatories at Berlin and Potsdam, an important role was played by Carl Bosch, the eminent chemist. As an enthusiastic amateur astronomer, an influential captain of industry and patron of the sciences he was in close touch with the astronomers and took an interest in stimulating their discussions. He was interested above all in the project for a great reflector telescope of 2 m aperture with a principal reflector of quartz, experiments for the manufacture of which were undertaken at his request at BASF in Ludwigshafen. This plan for a national observatory was bedevilled by prolonged wrangling between the astronomers, as to whether the instruments should be set up in the southern hemisphere for research on southern skies - one location under consideration lay on the outskirts of Windhoek in erstwhile German Southwest Africa - or in the northern hemisphere, in the Mediterranean region.

Even when political developments eventually caused all these schemes to founder, the idea still remained alive: after Carl Bosch had been chosen in 1937 to succeed Max Planck as president of the Kaiser Wilhelm Society, he strove to realise the idea by the establishment of a Kaiser Wilhelm Institute for Astronomy. The first funds for preparatory work were provided in the budget of the Society in 1939 and entrusted to the then Director of the Göttingen Observatory, Hans Kienle.

After the war an important stimulus was imparted by the report of the German Research Community, published in 1962, entitled "The Status of Astronomy", coauthor of which was Hans Elsässer, later to become the head of the new Max Planck Institute for Astronomy (MPIA). It became clear, amongst other things, that the problems of research urgently required a few establishments of supra-regional status, "which should transcend the scope of an individual university institute and stand at the disposal of German astronomy as a whole". For optical astronomy the recommendation again was for a powerful telescope in a favourable observational climate outside Germany. The impending creation at that time, after protracted negotiations, of the European Southern Observatory (eventually located in Chile) with the Federal Republic of Germany as one of five member states was indeed a ray of hope, but in no way a panacea for our national failings. Around 1960 the most powerful German telescope was still the l m telescope of Hamburg Observatory, dating from the year 1910, the second most powerful was the 72 cm reflector at Heidelberg, dating from the year 1906!

At a time when government and public opinion were aware of the requirements of science to a degree scarcely conceivable today, these arguments could not fail to be effective, although it was clear that the capital investment required would be very great. First of all, however, it proved to be unexpectedly difficult to find a suitable responsible body for the proposed establishment; the cultural federalism of our political system stood in the way. Then in the spring of 1964 the then president of the Max Planck Society, Adolf Butenandt, and his subsequent successor Reimar Lust assumed responsibility for the project. By virtue of its supra-regional character, the Max Planck Society had at that time become the strongest support of astronomical research in the Federal Republic. This applied not only in respect of optical astronomy, i. e. using visible light: extraterrestrial physics and radio-astronomy were at that time sponsored by newly founded institutes, whereas the predominantly theoretically oriented Institute for Astrophysics was considerably older. Excellent provision was thus made for the modern development of space science.

Drawn up in close liaison with the Council of West German Observatories, the concept of the new Max Planck Institute, whose foundation was approved by the Senate of the Max Planck Society at the end of 1967, and on which work was begun in 1969, originally appeared thus: a home-based Institute as headquarters, possibly in the precincts of a university, should be dedicated to the development of new measuring techniques and the construction of auxiliary apparatus for the telescopes. There also the observational programmes should be drawn up and the resulting data analysed. For the observations themselves, stations in both hemispheres were foreseen, in order to be able to cover both the northern and the southern skies. For the ideal solution in the north a location in the Mediterranean region readily accessible from Germany was envisaged. Both observatories should each have a telescope of about 2 m aperture, supplemented in the northern one by a 1.2 m telescope, already ordered by the German Research Community in 1967, and the great Hamburg Schmidt reflector. In order to avoid again falling behind similar establishments in other countries it was planned from the outset that one of the observatories - at first it was thought that it would be the one in the southern hemisphereÑshould have a large instrument with 3 to 4 m aperture.

Even when for reasons still to be mentioned several objectives had to be modified during the course of the years, and the present reality does not correspond in all respects to this ambitious plan, nevertheless it has been realised in its essential elements.

The Heidelberg Headquarters

The new buildings were erected between 1971 and 1975 on a 5.2 hectares site in the immediate vicinity of the State Observatory there, the earlier workplace of Max Wolf. The aerial photograph (Fig.1) gives a view of the whole establishment and its surroundings. The access road 1 through the forest approaches the establishment from the east. In the south wing of the strongly diversified main building are the offices and laboratories, whilst in the northern wing perpendicular to it are accommodated the workshops for instrument makers and electronic engineers, fitters and carpenters. The central part consists of cafeteria, administration, library and lecture hall. Standing apart to the south, crowned by two small domes, is the astrolaboratory for experiments with starlight and for trials of new apparatus.

According to the initial plan there were to be 150 members of the Institute, a number almost reached today. Of these only about one fifth are astronomers, the engineers and other technicians being more than twice as numerous. They cover a broad spectrum of expertise including laboratory physics, informatics, electronics, instrument making, photography and several others. In addition there is always a larger number of students of astronomy and physics working on graduate and doctoral theses at the Institute, which is also a much sought after training place for apprentices in instrument making and information electronics.

In addition to the functions and activities already mentioned, there are also at the Institute active working groups in the field of extraterrestrial astronomy. The extraterrestrial goals are not independent of the programmes of the Institute's ground based telescopes, but rather directed to associated problem areas. This has the desired effect that the different approaches are mutually supportive and strongly interactive.

The Observatories

Two qualities of the atmosphere above an observatory are of special importance: the "seeing" and the transparency. By seeing is meant the turbulence of the air caused by local factors. This leads to oscillations in direction of the light and causes blurring of stellar images in the telescope. Bad seeing therefore nullifies all attempts to obtain sharp images, which is the whole purpose in construction of the telescope. Moreover this will reduce the contrast in brightness against the celestial background and as a result reduce the range of the telescope. For many programmes doubling the seeing causes a loss of performance of the telescope corresponding to halving the aperture.

The seeing can be measured directly by transportable apparatus under field conditions, by taking long-exposure photographs of bright stars with a stationary telescope. Due to the rotation of the earth the star draws on the photographic emulsion a bright line, which is smoother, the less the seeing.

In addition to the seeing an essential attribute is the transparency, or degree of cleanliness of the atmosphere. It can be derived from measurements of stellar brightness, the increase of which up to culmination of the observed object yields information on unwanted absorption.

Northern hemisphere

The experience of more than a decade now available confirms that southeast Spain offers in Calar Alto the best conditions in the Mediterranean region of Europe. The hopes aroused by the test observations of frequent occurrence of first class seeing conditions have been fully realised: the diameters of the stellar images are not infrequently considerably smaller than one second of arc. Over the long term, with marked variations from year to year, about 180 observing nights are to be expected per annum, compared with 40 to 50 in middle European latitudes.

The negotiations with the Spanish authorities on the construction and operation of an observatory on Calar Alto extended over two years. The final terms of agreement, signed in 1972, consisted of a government treaty between the Federal Republic of Germany and Spain, as well as an agreement between the Max Planck Society and the Spanish Commission for Astronomy. The German commitment was to assume the responsibility for the scientific equipment and to undertake the entire construction of the observatory buildings and thereafter to provide for its current operation. The Spanish government provided the site for the observatory and a protected environment of nearly 100 square kilometres. It also undertook its development by the construction of power and water supplies as well as a 30 km access road. Spanish astronomers may use 10 per cent of the observing time at the telescopes, this portion corresponding to the share of financial contributions. Also in the naming of the observatory as the "German Spanish Astronomical Centre" the participation of Spain is acknowledged.

The construction work on the mountain began in 1973. The first telescope, the 1.2 m instrument financed by the German Research Community, was ready for service two years later and since then has been constantly in use. Today there are on Calar Alto four more telescopes (Fig.3): the 3.5 m telescope which was the result of more than 10 years' work by C. Zeiss at Oberkochen and accepted by us in 1984, another with 2.2 m aperture, the Schmidt reflector for photography of large celestial fields, transferred from Hamburg to Andalucia, and a Spanish 1.5 m telescope which is operated under the control of the Observatory of Madrid and is to be regarded as a visitors' instrument. Moreover in the last few years all the remaining buildings have been constructed, namely an Institute building with workshops and laboratories, living accommodation and a restaurant for the about 40 permanent members and the guest astronomers, the technical facilities building for the supply of the whole campus with water, heating etc. (Fig. 4). The completion of the first building phase with the commissioning of the 2.2 m telescope in 1979 was the occasion for a festive opening ceremony by the Spanish king and queen.

Southern hemisphere

The Gamsberg came into the possession of the Max Planck Society in 1970, and in the course of the years we have completed a small station, where not only the site testing observations, but also other observational programmes can be performed. In addition to a few huts for technical equipment and living quarters there is a hut with removable roof, in which a 50 cm telescope is housed. With it, amongst other things, thousands of photometric measurements on stars of the southern Milky Way have been carried out, which have considerably increased our knowledge of the galactic structure of the southern sky.

In March 1971, however, the Federal Minister for Science, Hans Leussink, responsible for the financing of the observatory and the telescopes, raised objections "on political grounds" concerning a site in Southwest Africa. He cited Resolution 283 of the United Nations of the previous year, in which member states were called upon to refrain from any projects or investments which could be interpreted as recognition and support of the South African regime in Southwest Africa.

Against this background, in 1973 the geographical latitude for the mounting of the 3.5 m telescope had to be settled. That this was then decided in favour of Calar Alto was not only for fear that the large telescope project could be jeopardised as a whole. In discussions with the scientific advisory board of the Institute special importance was attached to the question of how the worldwide geographical distribution of the large telescopes would develop, and whether a unilateral preference for the southern hemisphere was to be avoided. In this context one had also to consider, that the increasing air and light pollution in the western USA was increasingly hampering the mountain observatories in California and Arizona.

The second 2.2 m telescope, which had from the beginning been intended for the southern hemisphere, was put into production in 1970 by C. Zeiss, Oberkochen, together with the first (today installed at Calar Alto), and completed in 1976. There was at that time still the hope that the Namibian problem would in the meantime be clarified to such an extent that the installation of the telescope at the Gamsberg Observatory could be undertaken. This was, with hindsight, unrealistic: Southwest Africa is still in dispute and its situation is today essentially the same as then.

A practical way out of this frustrating situation first appeared when Italy and Switzerland decided to join as the seventh and eighth member states of the European Southern Observatory. The enlarged circle of ESO users called for adjustment in the form of an additional telescope at La Silla. According to an agreement made in 1980 it was arranged to loan the 2.2 m telescope II to the European organisation for 25 years. ESO has accordingly undertaken not only the burden of operational management, but also the costs of reconstructing the mounting originally planned for the Gamsberg site, the erection on the site and the new telescope building. The astronomers of the Max Planck Society are permitted to use the telescope for 25 per cent for their own purposes, the remaining time being distributed under the same rules as all the other instruments at La Silla between the observers of the member states, and hence also to those of the Federal Republic. This 2.2 m telescope was commissioned at La Silla in 1984, and the potential of the ESO observatory has thereby been distinctly enhanced. Gamsberg is accordingly, at least for the present, out of the reckoning. It should not be forgotten, however, since there are only a few remaining undisturbed sites of that quality, and the arguments presented in its favour are still valid.