Stockert Observatory and the Effelsberg Radio Telescope

Germany was excluded from the development of radio astronomy in the crucial years immediately after the end of the Second World War as restrictions on radio research were not lifted until 1950. But even then there were still many more important calls on state funding to rebuild the country after the war. So there was no sudden explosion of radio astronomy research in Germany in the early 1950s to match that already underway in Australia, the UK and elsewhere.

But starting in 1952 Friedrich Becker and H. Strahl gave a number of lectures about radio astronomy in local government ministries in Düsseldorf, the state capital of Nordrhein-Westfalen.(1) This resulted in the idea of building a 25 m diameter fully steerable radio telescope which could also be used for radar research. Design studies were carried out by Metallwerk Friedrichshafen and Telefunken who had built the German Würzburg radar antennae during the war. Enthusiastic backing for the proposed project came from Telefunken's former chief engineer Leo Brandt who was then Secretary of State in the Ministry of Economics and Traffic in Nordrhein-Westfalen. With his support 1.2 million DM (about $300,000) was raised to pay for the project which was undertaken by a consortium of companies headed by Telefunken.

The basic requirement of this 25 m radio telescope was that it should be able to detect radio emissions at the 21 cm wavelength (1.4 GHz) of neutral hydrogen and shorter if possible. This meant that its dish should have a surface accurate to about ±5 mm. It was also expected that the dish, which would be supported by an altazimuth mount, would be pointed to an accuracy of 1 arcminute. Naturally, considering the pedigree of the main contractors involved, the actual design was based on that of the Second World War 7.5 m diameter Würzburg radar antennae. The surface panels were of 2 mm thick sheet aluminium with 10 mm square perforations to reduce wind resistence. As far as location of the telescope was concerned, its use for radar research required it to be built with a good view of the horizon.

European Northern Observatory, Canary Islands

Night-time Telescopes on Tenerife

The Astronomer Royal for Scotland, Charles Piazzi Smyth, set up two small astronomical stations at high altitude on Tenerife in the Spanish Canary Islands in 1856. Although they were not there for very long, these observatories were the first to show the great advantage of observing at high altitude.(1) No one took much notice, however, and it was not until over fifty years later that Jean Mascart of the Paris Observatory suggested that an international astronomical observatory should be established on Mount Guajara on Tenerife. Discussions then started between the Spanish, French and German governments, but they were abandoned at the start of the First World War.

There was no progress with the idea of setting up an observatory at high altitude in the Canaries for a number of years. But astronomers observed a total solar eclipse from the Canaries in 1959. In the same year Spain founded the Observatorio del Teide at Izana, on Tenerife, at an altitude of 2,380 m (7,250 ft). A 30 cm (12 inch) French photopolarimeter was installed there in 1964 to study the zodiacal light, followed by a Spanish 25 cm heliographic telescope in 1969. The largest telescope at El Teide (now part of the European Northern Observatory) is the UK's 1.5 m Infrared Flux Collector (IRFC) that was built in 1971 as the prototype for the 3.8 m United Kingdom Infrared Telescope that was completed on Mauna Kea eight years later.

Site surveys carried out by JOSO (Joint Organization for Solar Observations) in the 1970s indicated that although El Teide on Tenerife was the better Canary Islands site for solar observations (see Solar telescopes later), the Roque de los Muchachos on La Palma was better for night-time observations. So although night-time telescopes continued to be built at El Teide (see Table 6.1), the largest such telescopes were built on La Palma (see Table 6.2).

Climax Observatory and the Sacramento Peak Solar Observatory

Donald Menzel of Harvard College Observatory had been instrumental in establishing the solar observatory at Climax, Colorado, or more properly the Climax observing station of Harvard College Observatory, in 1940. Unfortunately it soon became clear to Menzel and Walter Roberts, a former student of Menzel and the station's superintendent, that this Climax station suffered from long periods of cloudiness, especially during the winter. Consequently they concluded that a second solar observatory should be built as soon as possible after the Second World War had ended.(1)

At about the same time H. H. (Hap) Arnold, the commanding general of the U S Army Air Forces (AAF), had asked his scientific advisor Theodore Von Karman to draw up a long-range research and development plan for the AAF after the war. Arnold had been particularly interested for some time in meteorology, especially as it affected the air force. So it was no great surprise to find that Von Karman included, in his proposed long-range plan, research into the influence of the Sun on the Earth's ionosphere and atmosphere. Arnold and the AAF were not only interested in the effect of the Sun on the ionosphere and radio communications, but also its effect on the upper atmosphere through which guided missiles and supersonic aircraft would travel.

After the war Menzel happened to meet Marcus O'Day of the AAF's Cambridge Field Station who had been given responsibility for upper atmospheric research using captured V2 rockets. During discussions O'Day told Menzel that he also had access to funding to set up a ground-based solar observatory. As a result O'Day mentioned that there was a possibility that the Air Force might be able to support his proposed solar observatory. This case for support would be significantly strengthened if a suitable location could be found on the Sacramento Mountain Range close to the White Sands Proving Grounds from which O'Day was planning to launch his V2s.

In the meantime, following a proposal from Menzel and Roberts, in 1946 the Climax observatory became an independent research institution in its own right.(2) Called the High Altitude Observatory (HAO) it was affiliated with Harvard University and the University of Colorado with Roberts as its first director.(3) Its headquarters were at Colorado's Boulder campus.

ALMA

As mentioned previously (see Section 20.8) the NRAO had been trying in the late 1970s to get funding for a new 25 m (82 ft) millimeter-wave radio telescope to be built on Mauna Kea, but this had been killed off in 1982 by the Astronomy Advisory Committee. However, in the same year, an internal NRAO proposal was made to build a VLA-type millimetre array of fifteen 10 m diameter dishes on 1 km long arms. The plan was to build it near the VLA(1) at an altitude of about 2,100 m (6,900 ft) on the Plains of San Augustin, New Mexico. A little later, higher sites were considered in Arizona and New Mexico to enable the telescope to operate down to a wavelength of at least 0.85 mm (frequency 350 GHz). Then in 1990 the NRAO proposed what was called the Millimeter Array (MMA) which was to consist of forty 8 m diameter dishes, with a total area of 2,000 m2, at a cost of at least $120 million.(2) It would operate in the wavelength range from 10 mm to 0.35 mm (frequencies 30 GHz to 850 GHz)(3) and be built on a site about 3 km in diameter at an altitude of about 2,500 m (8,200 ft) in Arizona. At this stage the NSF, the potential funding source, let it be known that they expected that any large project of this nature should involve a number of international partners. By the mid 1990s, the NRAO were considering much higher sites on Mauna Kea or on Llano de Chajnantor at an altitude of about 5,000 m (16,400 ft) in the Atacama Desert to enable the array to operate well into the submillimetre range.

In Japan, meanwhile, the Tokyo Astronomical Observatory had built the Nobeyama Millimeter Array in the 1980s (see Section 23.5) which consisted of a number of 10 m dishes operating down to 0.8 mm. They followed this with plans to build an array in northern Chile consisting of fifty 8 m or 10 m diameter dishes called the Large Millimeter and Submillimeter Array (LMSA) to operate down to 0.35 mm.

Astronomers at the University of Arizona started planning in the early 1980s for an international observatory on the 10,700 ft (3,250 m) Mount Graham, the highest peak in the Pinaleno range, about 75 miles (120 km) from Tucson, Arizona. Mount Graham was chosen because of its low light pollution, low atmospheric water vapour, ease of access, and excellent seeing which was only a little worse than that on Mauna Kea. The planned telescopes included the 1.8 m Vatican Advanced Technology Telescope (VATT) of the Vatican Observatory, a submillimetre telescope (later called the Heinrich Hertz Submillimeter Telescope – see Section 23.6), and an optical-infrared binocular telescope, then called the Columbus Project, which consisted of two 8 m primary mirrors on a common mount.

For a time Mount Graham was also considered as a possible site for the National New Technology Telescope (NNTT, see Section 3.2). This was strongly advocated by the University of Arizona as they were hoping to supply its mirror. But Mauna Kea was eventually chosen in 1987 as its location after three years of site surveys, with Mount Graham as a backup.

Vatican Advanced Technology Telescope (VATT)

In the meantime the University of Arizona's Mirror Laboratory had spun-cast the 1.8 m, f/1.0 primary mirror blank for the VATT in 1985. In the same year construction work was also expected to begin on the VATT's new observatory building on Mount Graham, but environmental concerns over the mountain's red squirrels and its other sensitive habitats led to a series of delays.

The prospect of being able to build an astronomical observatory on Mount Graham received a major setback in June 1987 when the Mount Graham red squirrel was declared an endangered species. But it appeared as though the environmental impasse had been broken in October 1988 when university-sponsored legislation was passed by the United States Congress to allow the three planned telescopes to be built on the mountain without Forest Service approval. This legislation allowed the university to build four more telescopes, if the first three were found to have had a minimal impact on the red squirrel. But in March 1990, a Federal judge ordered a temporary halt to the observatory construction. Although this temporary injunction was overturned by the US Court of Appeals two months later, other potential legal problems had also arisen.

The Early Years

Martin Ryle, Bernard Lovell and a number of other people who became leaders in British radio astronomy had worked for the British Telecommunications Research Establishment (TRE) during the Second World War. John (Jack) Ratcliffe, who had previously led a research group at Cambridge University's Cavendish Laboratory also worked at TRE as one of its top administrators. But in early 1945 Ratcliffe left TRE to rebuild his radio research group at Cambridge where he was able to attract Ryle, Derek Vonberg and F. Graham Smith amongst others.

When Ryle joined the Cavendish laboratory the sunspot cycle was on its way towards solar maximum. As a result Ratcliffe suggested to Ryle that it may be a good time to investigate the source of radio noise associated with sunspot activity that had been observed by Stanley Hey during the Second World War.(1) But unfortunately at that time a typical radar antenna, operating at a wavelength of 1.5 m, had a beamwidth of the order of 10° making it impossible to find the exact source of radio waves on the Sun. So in the winter of 1945–1946 Ryle decided to build a radio interferometer which should be able to locate the sources much more accurately. It consisted of two antennae working at 175 MHz (λ 1.7 m) at separations of up to 240 m or 140 wavelengths. Each antenna was made of eight half-wave dipoles mounted over a wire mesh reflector. With this system Ryle and Vonberg were able to show that short duration radio bursts from the Sun were often circularly polarised and came from discrete areas on the Sun's disc, and not from the disc as a whole.

Two years later Ryle and Smith used another Michelson interferometer at Cambridge to study the cosmic source Cyg A, which Hey, Parsons and Phillips had found in 1946 fluctuated over a period of a few seconds. Ryle and Smith's interferometer consisted of two groups of four Yagi antennae spaced 500 m apart, operating at 80 MHz (λ 3.75 m).(2)

Spun Honeycomb Mirrors

The second half of the twentieth century saw the development of three different designs of primary mirror for large optical reflectors. These were spun honeycomb mirrors as used in the Vatican Advanced Technology Telescope on Mount Graham, segmented mirrors (see Section 4.2) as used in the Keck Telescope on Mauna Kea, and thin meniscus mirrors (see Section 4.3) of the sort used in ESO's New Technology Telescope on La Silla. A fourth type, a liquid mirror (see Section 4.5), was also developed, but this had more limited applications. This present section outlines the development of spun honeycomb mirrors as produced at the University of Arizona's Steward Observatory Mirror Laboratory.

The Multiple Mirror Telescope (MMT) had been completed at the Whipple Observatory on Mount Hopkins, Arizona in 1979 with six 72 inch (1.8 m) honeycomb mirrors. These mirrors, made of low expansion, fused silica glass, had been obtained as Air Force surplus equipment. The design of this MMT (see Chapter 10) was innovative in many ways. For example, the observatory building had been designed to allow rapid air movement across both the mirror and telescope structure, allowing them to achieve ambient temperatures quickly and stay there. The honeycomb structure of the mirrors also assisted this.

Neville Woolf of the University of Arizona suggested to his colleague Roger Angel that he look into the possibility of building a larger telescope than the MMT of the same general design.(1) Angel was impressed by the performance of the MMT's honeycomb mirrors and decided to look into the possibility of building larger ones without using expensive low-expansion glass. Instead, Angel and his graduate student John Hill decided to use borosilicate glass, as not only was it cheaper but it had a much lower melting temperature than the low-expansion alternatives, making it easier to cast.

Honeycomb backing for mirrors had been around for some time. The design, which was then called cellar or ribbed, had first been suggested by George Ritchey in the 1920s,(2) and had been used in a modified form for the 200 inch (5 m) Palomar Telescope that saw first light in the late 1940s.

Mount Wilson

Michelson had designed a stellar interferometer for the Mount Wilson Observatory in 1920 that consisted of a 6 m (20 ft) long steel girder and two 15 cm (6 inch) movable mirrors which he mounted across the open end of the 2.5 m (100 inch) telescope.(1) This enabled Michelson and Pease to measure the diameter of a number of red giants. However, little more interferometric work was done on Mount Wilson until 1979 when Michael Shao and David Staelin of the Massachusetts Institute of Technology designed a two telescope, white light, 1.5 m (5 ft) baseline interferometer. It was the first interferometer to compensate for atmospheric turbulence by making continuous phase and amplitude measurements with a 4 ms integration time. The Mark I was succeeded by the 3.1 m Mark II interferometer which was used as a technology testbed for astrometric measurements from 1982 to 1984. It incorporated a high speed, ultra high accuracy, laser controlled optical delay line, and it was also used to develop an operational procedure for rapid switching between stars. The Mark II was, in turn, followed by the Mark III(2) from 1986 to 1993 which had a maximum baseline of 32 m and operated in two spectral bands from about 400 to 600 nm and from about 600 to 900 nm. Like the Mark II, the Mark III was designed to test out new techniques and technologies. Its aim was to be reliable and easy to operate, whilst being capable of extremely accurate astronomical measurements of stellar positions and diameters. Lessons learnt in operating the Mark III were applied to the design of the US Naval Observatory's NPOI (Navy Prototype Optical Interferometer, see Section 14.6) located in the mountains near Flagstaff, Arizona which became operational in 1996.

Berkeley Infrared Spatial Interferometer (ISI)

Instead of using the Michelson homodyne or direct detection system of the above instruments, Charles Townes, Mike Johnson and Al Betz of the University of California (UC) at Berkeley(3) used a heterodyne system in 1974 to produce the first mid-infrared interferometer based on techniques used in radio astronomy.

Introduction

Hawaii was an important location for geophysical and astronomical observations during the International Geophysical Year (IGY) of 1957–58 because of its relative isolation in the middle of the Pacific Ocean. As a result, a number of such observations were planned but, unfortunately, there was not enough time nor money to establish all the facilities required. For example Walter Steiger of the University of Hawaiʻi (UH) had been hoping to establish a solar observatory in Hawaii, and in 1955 he had started site testing at the top of the 3,060 m (10,040 ft) high Haleakala, a virtually extinct volcano on the island of Maui. These tests indicated that Haleakala would be an ideal location for a solar observatory, but because of financial and timescale limitations Steiger had to settle, instead, for establishing a sea-level observatory on the island of Oahu.

Fred Whipple had also asked if the UH could build a satellite tracking station on Haleakala for the duration of the IGY. In this case he arranged for money to be provided in a rather round about way. He persuaded his old friend Kenneth Mees, a retired senior executive of Kodak and photographic scientist, to donate a number of Kodak plates to the UH so they could sell them and use the money to establish the tracking station. As a result the UH was able to acquire a plot of land on the summit not only for the satellite tracking station, which became operational in 1957, but, hopefully, to accommodate a future solar observatory there. At about the same time the United States Weather Bureau/National Bureau of Standards established an atmospheric research station at 11,120 ft (3,390 m) on the relatively stable northern slope of the active volcano Mauna Loa on the main island of Hawaii. Finally groundbreaking took place in February 1962 for the solar observatory on Haleakala. Dedicated two years later it was named the C.E. Kenneth Mees Solar Observatory in honour of the former Kodak senior executive.

Mitsuo Akiyama of the Hawaii Chamber of Commerce sent letters to many American and Japanese Universities in June 1963 suggesting that they consider the possibility of setting up an astronomical observatory on either of Hawaii's two large volcanoes, Mauna Kea and Mauna Loa.(1)

Radio astronomy took some time to take off in America after the pioneering observations of Karl Jansky in 1932 and of Grote Reber in the late 1930s and early 1940s. This was in spite of the tremendous advances in radio technology achieved during the Second World war. Although the US Army Signal Corps had detected radar signals from the Moon in 1946, this was not for astronomical purposes but was a test of their system to detect incoming missiles from the Soviet Union.

At the end of the Second World War American astronomers had access to the best optical telescopes in the world and the Palomar 200 inch was also shortly to become available. In addition the climate in the United States, particularly on the west coast, was generally good for optical observations. So observational astronomers in America saw no need to get involved in the new-fangled field of radio astronomy which required new technical skills that they generally did not have. They were also generally sceptical that radio observations would yield much in the way of useful astronomical results. In Europe, on the other hand, the climate was generally not as conducive for optical observations as in America and large optical telescopes in Europe were not as good. But the climate was no limitation for radio observations. So a new set of observational astronomers, largely ex radio and radar engineers and physicists, grew up in Europe after the Second World War devoted to radio observations. A similar situation prevailed in Australia which also suffered from a lack of top quality optical telescopes, although they did not have the same climate problem as in Europe.

By the early 1950s radio astronomy was beginning to produce interesting results. At that time it became clear in the United States that, unless a bold approach was taken, it would continue to fall further and further behind other countries, particularly the United Kingdom and Australia, in radio astronomy. As a result, a number of American organisations had either started to develop radio telescopes or were considering doing so.(1) Then in January 1954 an interdisciplinary conference took place on radio astronomy, jointly sponsored by the American National Science Foundation (NSF), the California Institute of Technology (Caltech) and the Department of Terrestrial Magnetism of the Carnegie Institution.

This book is a history of modern astronomical observatories and their telescopes. As such it covers the history of optical/infrared and radio/microwave observatories and telescopes that have been built since the Second World War. I have tried to cover the most innovative and trend-setting professional facilities and, as a result, I have excluded a discussion of most of the optical observatories established before the war even though some of them were still adding telescopes after 1945. This is because most of their new telescopes, with few exceptions, were not really innovative.

In many ways, the Palomar Observatory can be seen as the last of the major pre-war optical observatories as its first telescope, its 18/26 inch (46/66 cm) Schmidt, was built in the mid 1930s and its two main telescopes, the 200 inch (5.1 m) and the large Palomar (Oschin) Schmidt, were largely designed before the war. So maybe it should be excluded from this book, even though building of its two main telescopes was not completed until the late 1940s. But Palomar designs were innovative in many ways, setting the standards for large optical telescopes and observatories for some time to come. Consequently, I have begun my narrative with a brief outline of the design and development of the Palomar Observatory.

Ground-based astronomical observatories these days consist of more than just optical/infrared and radio/microwave facilities. For example, a number of neutrino, cosmic-ray, gamma-ray and gravity-wave observatories have been built, but I have excluded these to avoid complicating the book. Likewise, I have excluded small professional and large amateur facilities, interesting though many of them are, as this would take the book into completely new territory and make it considerably longer.

Discussing the history of professional astronomical observatories has its challenges as there are so many of them and their histories are often interconnected. It is theoretically possible to consider their history as one large interconnected story, but to produce a readable text I would have had to leave out interesting details which, in my opinion, would have made the book less interesting.

Active Optics

Active optics is usually understood to refer to a low frequency control system applied to the primary mirror of large reflecting telescopes. It corrects for optical aberrations like spherical aberration and astigmatism either detected in the initial set-up of the telescope or caused by flexure of the mirror as the telescope's orientation is changed or its temperature varies. To make the corrections an active optics system detects errors in the mirror's surface shape either directly or via its effect on astronomical images and corrects them using a motorised support system under the mirror. The mirror can be either monolithic, in which case the flexure function has no discontinuities, or segmented where the flexure function is discontinuous.

The first significant step on the road to designing an active optics system appears to have been taken by André Couder in 1931 when he suggested that the astigmatism of inadequately supported mirrors could be corrected by applying appropriate forces to the back of the mirror. Astigmatism left over after mirror manufacture could also be corrected in this way. But he could only measure the astigmatism qualitatively off-line making such corrections cumbersome and slow. As a result his suggested procedure was limited to the initial setting up of the telescope, rather than being applied continuously as in a modern active optics system. Independently Dmitri Maksutov appears to have come up with a broadly similar proposal in 1948, but it had the same limitations.

Technological developments in computer and sensor systems after the Second World War began to make it possible to design much more sophisticated active optics systems. In the event the first major telescope to use a form of active optics was the Multiple Mirror Telescope (MMT) which consisted of six identical 1.8 m telescopes on a common mount. The MMT was designed to bring all six images to a common focus on its central axis. It was planned to continuously monitor the flexure of the structures of the six individual telescopes using an internal laser system, and to correct them in real time to ensure that all six images coincided.

ARC 3.5 m Telescope

The University of Washington (UW) decided in 1965 to expand its astronomy department and hired Paul Hodge and George Wallerstein from the University of California at Berkeley to increase the number of astronomers in the department to three!(1) Not surprisingly, the facilities available at UW were quite inadequate for modern observational research so Hodge and Wallerstein began to consider how to improve them by building a large modern observatory. There were two major issues to resolve before they could go any further. It was obvious that the UW astronomy department was too small to afford a large astronomical telescope, and there were not enough astronomers to properly utilise such an instrument even if they could raise the funding. In addition there were no suitable locations in Washington State to make optimum use of a large modern telescope, so a site survey was required to find a suitable site elsewhere. The UW Regents authorised construction of a large telescope providing funding could be found, but Wallerstein and Hodge were unable to organise a suitable consortium to finance the project. As a result the UW built a small observatory on Manastash Ridge in Washington State as an interim measure at which they installed a 30 inch (80 cm) in 1972.

In the meantime the astronomy department at UW had continued to grow and rely heavily on the national observatory telescopes on Kitt Peak and Cerro Tololo for large modern telescopes. But, unfortunately, these were beginning to become heavily oversubscribed. Clearly the UW needed their own large telescope, even if it had to be with one or two other organisations in order to raise the finance.

When Alex Kane of Ashland, Oregon died in 1975 he left an estate worth $250,000 to build a large telescope. He initially intended to leave the money to Oregon State University but they were not interested in building a new large telescope, so he left it to the UW instead. Unfortunately the money was not sufficient, on its own, to pay for the facility that the UW had in mind. At first they discussed the possibility of building a joint telescope on Mauna Kea with Stanford University or the University of Vienna, but these discussions came to nothing.

Next Generation Telescope (NGT)

No sooner had the 200 inch (5.0 m) Palomar Telescope been completed in 1948, than some astronomers started to consider whether it would be possible to build an even larger instrument. One of the most determined was Aden Meinel who, in the early 1950s, produced the outline design of an optical reflector of about 500 inch (~12.5 m) diameter. In this the primary mirror was not to be made of one piece of glass, but of several hundred smaller mirrors. But he received little support for his ideas, particularly when the question of funding was raised. It was also not clear at that time whether it was feasible to build such a machine.

Twenty years later, the design of a very large telescope was readdressed by Leo Goldberg the director of KPNO. Telescope design had moved on since Meinel's work, and by 1974 the main building phase of telescopes at KPNO had been completed, leaving a number of talented engineers with relatively little to do.(1) So Goldberg asked these engineers to examine possible designs of an optical telescope with a collecting area equivalent to a 25 m (~1000 inch) diameter mirror.

KPNO's first design concept for this very large telescope, called PALANTIR or rotating shoe telescope, consisted of a 75 m long by 25 m wide segment of the primary mirror which could be rotated in azimuth. This primary was composed of hundreds of polished aluminium segments. The secondary mirror assembly, which included a 3 m secondary mirror, was mounted on the elevation axle, which was parallel to the shortest side of the primary. By moving about this axle, the secondary could view the sky from the zenith down to about 30° above the horizontal. The main advantage of this design, over a conventional one, was that the primary mirror could be rigidly held and did not suffer from variable gravitational forces as the telescope looked at various parts of the sky.

Unfortunately, the proposed resolution of PALANTIR was rather poor, its secondary mirror could only see a fraction of its primary at any one time, and its capital cost of about $160 million was completely out of the question at that time.

Mount Stromlo, the Early Years

Unlike many optical observatories discussed in this book the foundation of the Mount Stromlo observatory in Australia goes back to before the Second World War. In fact the idea of building a solar observatory in Australia goes back to before the First World War when Walter Duffield, an Australian working at the University of Manchester in the UK, pointed out its potential advantages. Not only would it fill the coverage gap in observing the Sun from the western Pacific, but it would also offer excellent observing conditions during the northern winter when the northern solar observatories were often compromised by poor weather and limited daylight.

In 1909 James Oddie, a wealthy philanthropist, donated a 9 inch (22 cm) Grubb refractor to the Commonwealth government of Australia to be the basis of a new national observatory, and the trustees of Lord Farnham's estate donated a 6 inch (15 cm) refractor to the observatory ‘if and when it was founded’.(1) A board was then appointed by the government to find a suitable site near Canberra, the capital of the new Commonwealth of Australia. Two years later the board chose Mount Stromlo, at an altitude of 2,530 ft (770 m), where the 9 inch was installed to undertake site testing. But the First World War was to intervene before a firm decision could be taken to build the observatory. In the event, building of the Commonwealth Solar Observatory was finally begun at Mount Stromlo in the mid 1920s.

Although the main work of the observatory was observing the Sun, it also undertook other astronomical observations. For example, in 1924 John Reynolds, a British engineer and amateur astronomer donated a 30 inch (75 cm) reflecting telescope with equatorial mounting for photographing nebulae of the southern sky, and William Rimmer used the Oddie refractor to measure the parallaxes of the brighter stars. But the most important work of this early period was undertaken by Clabon Allen who used a newly completed vertical solar telescope with an 18 inch (45 cm) coelostat and 12 inch (30 cm) objective to produce a comprehensive photometric atlas of the solar spectrum.

An Advisory Committee on Astronomy had been set up by the Carnegie Institution of Washington in 1902 to report on the likely advances to be made in astronomy and how they could be supported.(1) Chaired by Edward C. Pickering, the director of the Harvard College Observatory, the committee recommended that an observatory should be set up in the southern hemisphere as there were, at that time, ten times as many observatories in the northern hemisphere as in the southern.(2) Although William Hussey of the Lick Observatory was given a small grant to undertake a site survey, nothing came of the idea of a southern observatory at that time.

The idea of a large new observatory in the southern hemisphere was resurrected by George Ellery Hale in the 1920s when he suggested that it should include a 100 inch (2.5 m) or 60 inch (1.5 m) telescope. He even suggested that if a new 60 inch could not be afforded then the current 60 inch at the Carnegie Institution's Mount Wilson Observatory should be relocated there. Walter Adams continued to push for a Carnegie southern observatory after he became director of the Mount Wilson Observatory in 1923. In 1931 Henry Norris Russell proposed that the southern observatory should have a 150 inch (3.8 m) telescope whilst three years later Adams suggested that it should be a 120 inch (3 m). But the collapse of the United States stock market in 1929, and the ensuing depression, meant that such proposals had to be put on ice.

The idea of a Carnegie southern observatory was reintroduced in 1962 when Merle Tuve, a director at the Carnegie Institution, asked Ira Bowen, Horace Babcock and Robert Leighton to outline long-range plans for the Institution's Mount Wilson Observatory. In response they produced a list of six major projects, one of which was the southern observatory. Separately Bowen suggested to Caryl Haskins, the president of the Carnegie Institution, that this observatory should include a 140 or 150 inch in order to compete with the telescopes planned in the southern hemisphere for the European Southern Observatory, the Anglo-Australian Observatory and AURA's Cerro Tololo Inter-American Observatory.