Smyth in 1856. Isaac Newton had written: “[Telescopes] cannot be so formed as to take away that confusion of rays which arises from the tremors of the atmosphere. The only remedy is a most serene and quiet air, such as may perhaps be found on the tops of the highest mountains above the grosser clouds.” Following this principle Smyth tested El Teide, the main peak of Tenerife, for its suitability to sustain astronomical observations. In the course of a voyage lasting 113 days in 1856, he spent 65 days at Guajara and Alta Vista on the slopes of El Teide at heights of 2,714m and 3,262m respectively. He performed tests of seeing by separating double stars and extended the magnitude limit of his 18cm refractor by 4 magnitudes to 14th magnitude from its habitual 10th magnitude at Edinburgh. He made meteorological observations of humidity, dew point, windspeed and dust-haze as well as numerous special astronomical observations designed to demonstrate the quality of the sky, for example of solar prominences, zodiacal light, and solar spectra.

In January, 1967, Hermann Brück, Astronomer Royal for Scotland, first proposed the construction of a Northern Hemisphere Observatory (NHO) equipped with a 150-inch telescope. Exactly two years later, a committee under Fred Hoyle convened to examine the feasibility of such an undertaking, and by mid-1971 the project was in the planning stage.

The choice of a site was strongly influenced by Merle Walker of Lick Observatory and his extensive investigation of the factors determining good observing conditions. Walker developed the technique of examining trails of circumpolar stars as a means of measuring the steadiness of the Earth’s atmosphere. He carried out such observations at sites around the world.

Early in 1971 he wrote that “the best seeing occurs at sites on peaks near sea-coasts having cold ocean currents offshore that reduce the height of the [temperature] inversion layer, and where the laminar air-flow set up over the ocean still persists” (Walker, 1971). And he also concluded that “mountain peaks on (small) islands in warm oceans may be good sites, provided that the peaks are sufficiently high to place the observer above the inversion layer…” The importance of an inversion layer is that clouds get trapped below it, leaving clear skies above. On the basis of all the available evidence, Walker produced a list of potentially favourable observing sites that included Tenerife and its near neighbour La Palma, as well as Madeira, Corsica, and Crete.

As is often the case in scientific endeavours, several people reached the same conclusion simultaneously. Walker was not alone in recognizing the Canary Islands’ potential. In 1971, John Alexander of the Royal Greenwich Observatory was investigating possible observing locations in the Mediterranean area, and his quest took him to La Palma in April 1971. His report, published later the same year, stated: “The ideal solution may be an international observatory site on the island of La Palma.”

Moreover, European solar observers, joining in an association known as JOSO (Joint Organization for Solar Observations) visited Tenerife in 1971 March, and on their second visit in November 1971, flew in a light aircraft over the mountain top of La Palma testing for atmospheric turbulence with temperature sensors. The possible sites on La Palma were inspected by several JOSO site testers in summer and autumn 1971. The highest point at El Roque de Los Muchachos (2426 m) was selected as a possible site. 

The first observations on La Palma

The first astronomical (solar) observations on the Roque de Los Muchachos peak were carried out by a JOSO team consisting of Göran Hosinsky, Lars Staveland and Hubertus Wöhl from 2 to 21 July 1972 (Hosinsky, Staveland and Wöhl, 1972). 

The British site-testing teams were dispatched to Tenerife and La Palma in 1972 under the direction of the Royal Observatory Edinburgh (ROE). The survey on Tenerife was made at the well-developed site of the Observatorio del Teide. Conditions on La Palma were very different. Rising to almost 8,000 feet at its highest point – called Roque de Los Muchachos – the caldera’s rim is a desolate region of scrub vegetation and volcanic ash. The site under investigation was Fuente Nueva, a small peak on the northern edge of the caldera adjacent to the Roque. The survey took place in August and September, 1972. This is an extract of probably one of the first publications with data taken at the Roque de los Muchachos Observatory (B McInnes, 1974)

“The main work of the Project in the Canary Islands was done on the island of Tenerife; it seemed desirable to have some information also from the island of La Palma. A visit was made to the island during 1972 July 11 to 14 and decisions were made about the observational work that could easily be done there at that time. Dr Gough and Mr Heath then assembled the necessary equipment in Tenerife for a temporary outstation. They arrived at La Palma on July 28 with the Station 3 Land Rover carrying the equipment; construction work and transportation of the equipment to the site occupied the next few days; the observations began there on August 6 and ended on September 24. The highest point of the island is Roque de los Muchachos (2,423 metres, 7,949 feet). The site chosen for the observations was a peak called Fuente Nueva, situated about one kilometre north-east of Roque de Los Muchachos […] This site was selected by Dr Gough in the expectation that there might be a more favourable airflow there than at the higher Roque de Los Muchachos, since the prevailing wind is from the north and there is a fairly uniform slope with a gradient of about 1 in 4 from Fuente Nueva down to the coast, which is about 9 kilometres (5.5 miles) to the north. Observations of the seeing were made using a Lick Polaris Trail Telescope, which was mounted on a pier constructed of concrete blocks and local rocks cemented together. The objective of the Polaris Trail Telescope was about 4 metres (13 feet) above the general ground level. In general, seeing observations were made each hour during the night and meteorological observations were made at the beginning of each seeing observation. The air temperature was read from an accurate sheathed thermometer which was housed in a louvered box. The wind speed was measured with a hand-held anemometer, held at about the height of the telescope objective. The wind direction was obtained from a wind vane which was mounted at about 5 metres (16 feet) above the general ground level. Since there was no road to the site, access was on foot, with mules to carry equipment and supplies, and the observers were housed in small tents. The walk from the nearest vehicle road to the site took between two and three hours.”

The results of this preliminary testing campaign were analyzed by Walker and Bennet McInnes of ROE and published in 1974. Their conclusion was that the “seeing conditions at Izaña, while good, were not excellent.” On the other hand, reports from Fuente Nueva “indicate conditions as good or better than those known at any other site.” Additional factors, such as the number of clear hours and the lack of light or atmospheric pollution singled out the La Palma site as being exceptional. The JOSO came to a similar conclusion. Professor Kiepenheuer of the Fraunhofer Institut in Freiburg, Germanyand JOSO leader became an enthusiastic advocate of La Palma at this time.

Left: Observing the Sun on the top of the Roque de Los Muchachos with a 20 cm Maksutov telescope during the summer 1972 JOSO campaign [ TIFF ]. Right top: Part of the JOSO camp on top of the Roque de Los Muchachos in July 1972: (1) solarigraph; (2) delta T-sensor; (3) anemograph; (4) Maksutov telescope (20 cm) [ TIFF ]. Right bottom: Dornier 27, aircraft used for the scanning flights. [ TIFF ] (these pictures were extracted from the JOSO Annual Report 1972)

The mid 70’s Site Testing

In 1974 August the Spanish authorities issued an invitation to form a Joint Astronomical Site Survey to undertake an international programme of site testing on the Canary Islands. A momentous meeting took place in 1974 December, when representatives of Denmark, Sweden, Germany and the United Kingdom were invited by the Rector of the University of La Laguna and the Presidents of the local Governments (Cabildos) of Tenerife and La Palma to discuss arrangements for the survey programme. Meanwhile, arrangements had already been made for the setting up of Polaris trail telescopes and meteorological equipment on La Palma and observations began on 25 November 1974 and ended in November1975 .

Fuente Nueva base in 1975 (photo by Lluís Tomas Roig) [ JPEG | TIFF ]. More pictures of the 70’s site testing: Rein Bakker’s. | David Williams-Jones’.

This encouraging progress came after a period of deep pessimism about the prospects for agreement on the use of La Palma. At the sixth meeting of the NHO Planning Committee in May 1973, Sir Martin Ryle complained about the lack of progress and suggested that UK universities could themselves move faster and more effectively both on the international and the technical questions. Dr M J Smith, who acted as a consultant to the Planning Committee, reported on Hawaii as almost the only possible site. Testing on Madeira (Ecumeada Alta peak) as an alternative started in October 1973. Spanish sites were no longer to be considered.

Recovery from this deep gloom obviously depended on international politics, but it appears that several personal initiatives were also partially responsible. In March 1974 Prof S Edwards (Chairman of SRC) and Prof M F Walker visited the Consejo Superior de Investigaciones Científicas (CSIC) in Madrid and discussed the problem with Prof Masía, who was already well known for his help in international scientific affairs. Walker followed this visit with another in June. Prof F Sánchez, Director of the Observatory in Tenerife, had been encouraging the CSIC, the University and the local authorities to issue a joint invitation. A senior Spanish astronomer, Padre Romaña, was also active in overcoming the various political problems.

At the meeting of December 1974, representatives of the various countries involved: Prof K O Kiepenheuer (Germany), Prof A A Wyller (Sweden), Dr K Gyldenkerne (Denmark), Prof H A Brück and F G Smith (UK) were shown the La Palma site from a light aircraft. F H Smith wrote: “A small hut with the waving figures of two site testers was the only sign of human activity on what is now a major European observatory. The weather was good and we were assured that this was typical. Everyone felt that this must be the site for the new observatory” (F G Smith, 1985). From that time onwards there was intensive action on three fronts: site testing, telescope design and the necessary international agreements. (see site tester’s notes, Rein Bakker, on their work on site).

The meeting of 1974 December also revealed the intention of the Spanish astronomers and authorities to provide the basic facilities, ie a road, electrical power and water for the new observatory site. The project was to be regarded from the start as a cooperative venture, with the overseas participants providing telescope time and training for research astronomers in return for the use of the site and its facilities. The formal agreements necessary to secure the rights and specify the duties of the international participants were formulated two years later, when Prof Primo, President of the CSIC, invited representatives of research institutes in the various countries involved to Madrid.