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International Astronomical Union

Category of Astronomical Heritage: tangible immovable
Pic du Midi de Bigorre Observatory, France: English version

Format: Full Description (IAU Extended Case Study format)

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Midi Pyrénées Region, Hautes-Pyrénées Département


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Pic du Midi de Bigorre Observatory

Photograph © Haute Pyrénées Tourisme Environnem

Photograph © Haute Pyrénées Tourisme Environnement


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Latitude 42.9374 N, longitude 0.14106 E

UTM (Zone 31N) E 266729 N 4757829

Elevation 2830m (GoogleEarth)


Maps and plans,
showing boundaries of property and buffer zone 
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Fig. 1. Locality of the Pic du Midi de Bigorre within the Pyrenean Chain. Source: geographdumonde

Fig. 2. Extract from the IGN map, scale 1:50,000. The cable-car line to access the Pic du Midi, leaving from La Mongie,
crosses over the Taoulet before reaching the summit. Source: géoportail


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The observatory takes up the entire surface of the Pic du Midi de Bigorre summit, that is 3500 m².



Description of the property 
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    Author(s): Nicolas Bourgeois

<strong>Fig. 3</strong>. The Pic du Midi de Bigorr

Fig. 3. The Pic du Midi de Bigorre Observatory by night, in December 2013, facing the eastern horizon. 2013. Photo © Nicolas Bourgeois


The Pyrenees; a natural border of almost four hundred kilometres, at once separating France and Spain, and joining the Atlantic and the Mediterranean. As we approach this indented wall of snow-capped peaks, one of them immediately catches the eye, the Pic du Midi. Benefitting from an exceptional, seemingly even privileged geological location, this mountain stands at nearly 3,000 metres above sea level in the line of the Pyrenean foothills. It thus appears to dominate all the mountains surrounding it.

It is the mountain’s very position and presence which has for a long time captivated mountain dwellers, and later scientists. It has been home to history and human adventure for hundreds of years. But as Graham Greene said, there is no beginning or end to history, it is because of arbitrary decisions that we fix it in the river of time.

As we continue towards the Pic du Midi, it is no longer the mountain alone which holds our attention, but indeed the budding domes and grand aerial on its summit. Finally the Pic du Midi Observatory is revealed, a high-mountain scientific fortress which has stood strong for over 130 years.

Our arbitrary decision comes into play here. A new beginning, in 1870, the birth of the observatory and of human and scientific adventure. And now, not an end but an opening: 2014, the year in which the Pic du Midi decided to value and preserve what makes it an treasured inheritance, namely that it is the oldest mountain observatory still working today .

By presenting data on the features of the Pic du Midi (results, scientific publications and prizes, the number of researchers who have succeeded one another), we are able to show that despite its total isolation, the observatory has made significant contributions in a number of scientific fields which depend on findings at high altitude or in very pure atmosphere. In so doing it has itself evolved, keeping pace with the development of scientific knowledge.

However, whilst this information is essential, it is not enough to enable us to grasp the other dimension of the peak, that which makes it truly unique. If it is certain that the peak’s history has crossed paths with many scientific research institutions, this is essentially down to the high altitude and extreme isolation. It is for this reason that the singular identity of the Pic du Midi goes beyond the purely scientific realm. It is above all a matter of a human adventure still going on today, and it is this which accounts for the scale of the heritage we will try to describe here.


The Pic du Midi de Bigorre, an exception in Pyrenean geology

Nowhere on the north side of the Pyrenees is there a mountain of that altitude this close to the plain. Indeed, the Pic du Midi stands at 2,877 metres, where all the surrounding peaks reach 2,400 metres at best, 2,500 for the highest amongst them.

The Pic du Midi owes this characteristic to its geological structure. The rocks that form the pyramid are variable in nature: limestone massif, silicate minerals and schist on the top.This combination has been very much affected by intense metamorphism (the rocks have undergone temperatures of 600°C at pressures of tens of kilobars). The result of this metamorphism was a hardening of the rocks, a recrystallising of them. The limestone massif thus became more resistant to erosion than its surrounding neighbours.

Another outstanding result of the metamorphism is the presence of geological formations known as "barégiennes", in reference to the local town of Barèges. The barégiennes appear to be significant distortions of the geological domain. They are derived from the alternating siliceous beds (which deform rigidly) and carbonate beds (which deform plastically) having been subjected to the increase in temperature and pressure that occurred during the Hercynian period. These barégiennes look like huge, stone snakes and are at the origin of the tale of the legend of Python, the guardian of the Pyrène tomb.

<strong>Fig. 4</strong>. The Pic du Midi and the O

Fig. 4. The Pic du Midi and the Observatory, aerial view, 2010. Photo © Haute Pyrénées Tourisme Environnement

The atmospheric quality and the scale of the panorama

The geological characteristic of the Pic du Midi means that it benefits from two major assets: great atmospheric quality and stability, and a panoramic view of spectacular dimension.

<strong>Fig. 5</strong>. The Pic du Midi above the

Fig. 5. The Pic du Midi above the sea of clouds, 2009. Photo © Pierre Paul Feyte

The Pic du Midi’s altitude rises above the atmospheric vase. The latter consists of the lower layers of the atmosphere where we find dust, droplets and other particles. The summit is also situated in part of the atmosphere known as the lower troposphere. This layer establishes itself between 2,500 and 3,500 metres above sea-level. It reverses the natural temperature curve and keeps condensation blocked below the layer. When this limit of this layer is below the summit, the observatory stands above a sea of clouds, allowing access to a sky entirely devoid of particles and light pollution.

The position and altitude of the peak have another beneficial effect; atmospheric stability. The dynamics of the layers of air found in the upper troposphere (3,000 to 10,000 metres above sea level), depend on geomorphology. A mountain causes turbulence in much the same way as a stone falling into water would disturb the water’s surface. However, when the wind is oriented in a particular way (north, northeast), the first mountain that air masses reach, is the Pic du Midi. The flow of these streams is thus laminar, and with no turbulence between the summit and the stars.

It is this great atmospheric quality that marked the first Pic du Midi astronomers in the early twentieth century, and indeed that will allow us to conduct many research programmes on the properties of the atmosphere.

The summit, which rises up above all surrounding landmarks, lets us enjoy a view of exceptional dimensions. Count Russel liked to say that from atop the peak, you can see the foothills of the Massif Central by day, and the lights of the Biarritz lighthouse by night. His successors contemplating this could only confirm it.

The characteristics of this view are such that in 2003 the Pic du Midi was classified by the French government for the beauty of its landscapes. Indeed, on a clear day, the spectacular view offers up all 400 kilometres of the Pyrenean Chain.

The properties of this natural viewpoint were, in a way, the first foundations of the Pic du Midi Observatory which, almost a century and a half later, continues to use them in order to enrich both science and mountaineering in the Pyrenees.

Intangible heritage

The Pic du Midi Observatory’s contribution to the scientific knowledge of humanity over the 130 years it has existed is very rich indeed and covers a wide range of natural sciences.

The Pic du Midi has been and remains a first class astronomical site by the quality of the seeing and the transparency and purity of its sky both day and night. This quality is now guaranteed by the commitment of all the people working to preserve the sky above the peak through the International Dark Sky Reserve classification, a label which was attributed to the Pic du Midi in 2013.

The Pic du Midi plays a central role in spreading knowledge to visitors from around the world, as much about the quality of its preserved geological landscape, as the quality of its night sky, which is open to professional astronomers, amateur astronomers, university students, school children and the general public.

The use of the Pic du Midi as a place of scientific observation is rooted in the Enlightenment period, well before any building took place on the summit. Some of the great names in exploration made some interesting observations atop the peak. These observations were used for the drawing up of the topographical map of France and for pioneering new ways to measure atmospheric pressure at altitude (Cassini III in 1740, Monge and Darcet 1774, Lapeyrouse 1782).

The Pic du Midi is known worldwide for many discoveries of the modern era. Among these discoveries we can cite the following:

  • First ozone measurements in altitude using chromatography (Marchand, 1874, 1909). These measurements serve as a reference for the contemporary evolution of anthropogenic ozone pollution (tropospheric increases evaluated over 100 years by the current service. The Pic du Midi remains an international reference site for the quality of the troposphere, chemical measurements of CO, CO2, O3, NOx, mercury vapour, aerosols, and mass spectrometry of traces of radioactive elements; Pyrenean Atmospheric Observation Platform, Gheusi 2012). The Pic du Midi detected by mass spectrometry, traces of radioactive elements from Fukushima six months after the accident in 2012 (Van Beek, 2012).
  • Pioneering studies of atmospheric electricity and lightning (Dauzère). The Pic du Midi is now an international site for the study of Transitory Luminous Phenomena (or Sprites): these are the flashes which appear above thunderstorms (Soula 1990).
Cosmic rays and particle physics:
  • First measurements of cosmic rays and atmospheric electricity (Nodo 1907) 5 years before the discovery of cosmic rays by Hess V (1912).
  • The Pic du Midi became a hotspot for research on cosmic rays (Daudin 1948-1953) and particle physics after preliminary measurements (Cosyns from 1937, Auger 1938). The site welcomed international teams managed by P. Blackett (Nobel Prize 1948) and was the location for the fundamental discoveries of the pion (meson p, Occhialini 1947) and hyperon (1950) and then Leprince-Ringuet (1951-1953) with the installation of a bubble chamber and particle physics detector . The Pic du Midi was the main exploration site for this subject up until the foundation of the CERN in 1958.
  • The study of cosmic rays is experiencing a revival at the Pic du Midi with the recent installation of a Bonner high-resolution, spherical spectograph (Hubert 2013, ONERA, INRS) for studying the spectrum of telluric and cosmic neutron disintegration.
Solar Astronomy:
  • Pioneering photographs of the eclipse (18/07/1860) by Maxwell-Lyte from the meteorological station in Sencours: observations of the low solar corona using coronographic technique, a technique invented and tested by Bernard Lyot at the Pic du Midi from 1930 to 1940: see the Paris Observatory’s digital base, notably the first films of the solar flares by Bernard Lyot (1935-1936-1937), and films on sunspots and solar granulation by Bernard Lyot (1943).
  • Pioneering discoveries on solar granulation: the most precise solar observations from Earth using the Jean Rösch Telescope from 1961 to 1990. We can also quote the works of R. Muller on observations within the G wavelength (430,5nm) at very high resolution (seeing = 0.3 arcsec). T Roudier and M Rieutord on the dynamic of spots and magnetism (1990-2009).
  • Today, the observation service of the solar corona continues to observe the Sun with a Lyot coronograph (rebuilt in 2009), continuing a tradition which began almost a century ago on the Pic du Midi. The findings are stored in international databases managed by the Observatoire Virtuel du Grand Sud Ouest, for the use of astronomers worldwide.
Planetary Astronomy:
  • Observations of planet surfaces: (Henri Camichel, Audoin Dollfus, Jean Focas, Edward Bowell and John Murray: 1943-1963). Using the 60 cm Telescope in the Baillaud dome, and then the 1m Telescope, we have produced some of the best images taken from the Earth of the planets in our solar system. The measuring of planetary diameters, the measuring of the retrograde rotation of Venus’ atmosphere (Boyer 1957-1967). The mapping of the moon and preparing the Apollo mission (1964-1966, over seventy thousand shots, Manchester Lunar Programme).
  • Pioneering measurements of the distance between the Earth and the Moon using laser shots (Calame 1969).
Stellar Astronomy:
  • Today, the Bernard Lyot Telescope (2m) is the worldwide leader in the observation of stellar magnetism using the instruments MUSICOS (Boehm, Catala, Donati 2000-2007) and NARVAL (Semel, Donati, since 2007). Many pioneering discoveries were made and continue to be made in the study of magnetic fields across the HR diagram.
  • Current projects are moving towards monitoring the impact of magnetic fields on emerging exoplanetary systems (SPIP project, Donati) and exoplanetary systems which are ending (Boehm, Neo-Narval).
Instrumental Development:
  • The Pic du Midi has served, and continues to serve, as a testing bed for many different instruments. Examples include developments in coronography: a technique invented at the Pic du Midi by Bernard Lyot (1930-1931); polarimetry: pioneering instruments developed by French teams (Semel, Leroy, Donati); the first CCD, now in use in digital photo devices; semiconductor matrix detectors have been most notably developed and tested by Toulouse teams at the Pic du Midi (Strong 1980). The early development of instruments that correct atmospheric disturbances (telescope isolated from dome turbulence, Lyot, Rösch; Prieur tavelograph, 1991-1993).


Tangible heritage—a partial inventory

Immovable items—buildings and grounds

The Pic du Midi Observatory building is the culmination of 140 years of organisation and development of a complex and massive infrastructure which has been devoted to science and also to tourism since the 2000s.

The general architecture of the Observatory is a direct result of this long history and the continuity of its business. We observe typical mountain architecture (ogival roofs and stone walls extracted from the summit itself) and uniquely, more contemporary architecture, developed and designed specifically for the Pic du Midi (the Jean Rösch dome and the Bernard Lyot Telescope observatory).

The size, complexity and diversity of this platform’s activity, oblige us to focus solely on the heritage developed on the summit, at the expense of other fundamental elements of the Pic’s life: elements such as the Plantade Station on the Col de Sencours or even the Observatory of Bagnères de Bigorre.

Evidence of the desire to preserve the heritage of the Pic du Midi can be found in the excellent conservation of the scientific buildings which is largely due to tourist activity. Our description will therefore focus on these buildings.

The key periods in the evolution of the infrastructure are presented in the ’History and development ‘ section below.

<strong>Fig. 6</strong>. Aerial view of the Observ

Fig. 6. Aerial view of the Observatory after the "Pic 2000" project in 2000. The new elements of infrastructure are visible: the cable car station, the footbridges, the new coronograph building, and the modernising of the weather tower (2009). Photo © Claude Etchelecou

General description and key facts and figures in the Pic du Midi’s tangible heritage

We can imagine the Pic du Midi to be a small independent town perched on a peak at almost 3,000 metres above sea level. The general description that follows expresses this idea.

The Pic du Midi comprises:
  • A terrace covering 750 m²
  • 5 kilometres of inland corridors for link buildings and basements
  • 10,000m² of covered surfaces
  • 5 floors (8 if we include the floors in the Interdepartmental building: the equivalent of 10 storeys)
  • Annual electricity consumption is that of a French village of 600 people
General infrastructure

The three main infrastructures on the summmit: scientific infrastructure (buildings and observatories); touristic infrastructure (museum, restaurant, reception and conststructions for managing people movement); the interdepartmental building and its aerial.

The scientific and touristic infrastructures are interdependent whilst remaining dissociated. The observatories are only accessible to tourists under certain conditions and on certain occasions in order not to disrupt the activity.

The platform consists of the following:
  • 4 scientific and historic buildings on the terrace: the Vaussenat building, the Nanssouty building, the Marchand laboratory, the Dauzère building.
  • 7 astronomical observatories, 5 of which house scientific instruments which are still in use: the Bernard Lyot Telescope dome and observatory, the 1 metre Telescope dome and observatory, the Jean Röcsh dome and observatory, the Coronograph dome and observatory, the 60cm Telescope dome and observatory, the Charvin dome and, finally, the Baillaud dome.

For this thematic study, we will describe the main astronomical observatories which are still active and the Baillaud dome (the first astronomical facility to be installed on the summit). This selection allows us both to present a fully preserved and living heritage, and consequently to describe the instruments contained in these observatories in the section ’Movable heritage objects - Telescopes‘.

The scientific buildings of the Pic du Midi Observatory

The Baillaud Dome (1908)

The Baillaud dome was the initiative of Benjamain Baillaud, the director of the Toulouse Observatory at the beginning of the century. It was the first permanent astronomic facility to be installed on the Pic du Midi. Almost unused until the 1930s, it later became the centre of the Observatory’s astronomical activity. Indeed it was under this dome that Bernard Lyot invented and then tested his coronograph. Later, in the 50s, the dome housed powerful instrumentation, allowing us to take advantage of the transparent sky above the Pic du Midi. The Pic du Midi’s international prestige originated from the Baillaud Dome. Most of the scientific discoveries and contributions towards both planetary science and the study of the sun were made in this building.

Between 1904 and 1905, the dome was built and assembled for the first time in Toulouse, in the gardens of the Jolimont Observatory. From 1906 to 1907, it was transported by train, then by men and mules to the summit. On 14 September 1907, the dome was finished. Measuring 8 metres in diametre, the dome is sized in order to accommodate a 500mm telescope with a 230mm guider on the top.

For nearly 130 years, the Pic du Midi has been expanding and building around the first dome buildings. In the late 1990s, the dome ceased its activity. Preserved in its original state, it is now the highlight of the observatory museum space. Here, visitors find the first coronograph of Bernard Lyot and instrumentation presented.

<strong>Fig. 7</strong>. Construction of the Baill

Fig. 7. Construction of the Baillaud Dome in 1907. Photo © Alix, Fond Eyssalet

<strong>Fig. 8</strong>. The Baillaud Dome in 2013

Fig. 8. The Baillaud Dome in 2013. It houses the museum and the 1/1 scale model of the coronograph. Photo © Nicolas Bourgeois

The 1-metre Telescope Observatory and Dome (1947)

The 1 metre Telescope dome has been at the summit since 1947. Made in 1925 and based in Paris, the dome was given by Marcel Gentili, in recognition of the years he spent on the Pic during World War II, where he was protected from the Nazis. This dome, installed on the Dauzère building, originally housed the Gentili 60cm telescope.

In March 1962, the new 1 metre Telescope was installed to support the Manchester Lunar Programme. At this time, use of the dome proved to be an excellent opportunity for the NASA financed programme. Indeed, the experience gained on the Pic du Midi about the necessary conditions to obtain good images, allowed us to highlight the need for a small dome so that the thermal balance between the instrument and the air outside/inside would take place quickly. Due to a lack of resources to build a new dome, Gentili’s gift was accepted and served only to enforce the project.

This dome, which is today over a century old, has housed one of the Pic du Midi’s most efficient instruments for 50 years - the 1m Telescope.

 <strong>Fig. 9</strong>. The Dauzère building wh

Fig. 9. The Dauzère building where the Gentili dome was placed in 1947. Photo © Alix, Fond Eyssalet

<strong>Fig. 10</strong>. The Dauzère building an

Fig. 10. The Dauzère building and the Gentili dome in 2013. The integrity of the building has been fully preserved. Photo © Nicolas Bourgeois

The Jean-Rösch Dome and observation point, or Tourelle dome (1961)

The Tourelle dome is one of Jean Rösch’s pioneering and experimental projects at the Pic du Midi. This observation point complements and reinforces the work following the sun done under the Billaud dome. Rösch’s ambition was to create a unique type of observatory in order to enjoy the high atmospheric quality that the Pic offers whilst reducing the constraints inherent to solar observation with a conventional device (increase in dome temperature, image deteriation due to instrumentation, internal turbulence).

In order to create this dome, Jean Rösch called upon Jacques Pageault, who would design and construct the dome in the Bagnères Observatory workshop.

The dome has been installed on the extreme eastern end of the summit which is the ideal place to make the most of observation conditions in the morning, the best of the day. The dome was inaugurated on 15 February 1961, a day when a partial solar eclipse was visible.

The dome only measures 5 metres in diameter, but its design is such that it can accommodate an instrument which measures 6 metres long. The instrument’s lens is thus 2.5 metres outside the dome, which allows it to escape the structure’s internal turbulence. It is equally equipped with a cooling system for draining away the energy produced by the light beam. The interior walls of the dome are also isolated by a lining. The characteristics of this dome have been included in most solar telescopes built around the world after this one.

<strong>Fig. 11</strong>. The Tourelle dome was in

Fig. 11. The Tourelle dome was installed on the extreme eastern end of the Pic du Midi platform in order to make the most of optimal observation conditions early in the day (2013). Photo © Régie du Pic du Midi and Observatoire Midi Pyrénées

The Bernard Lyot Telescope dome and observatory (1978)

The Bernard Lyot Telescope dome and observation point were developed by Jean Rösch’s team in order to accommodate the biggest national telescope. This project came into being in 1966. Its location and architecture were determined by two conditions which are dear to the Pic du Midi astronomers: maximum use of the atmospheric stability offered by the Pic du Midi and creating the best possible balance between the structure and the instrument it houses (in the manner of the Tourelle dome and the Jean Rösch Telescope).

<strong>Fig. 12</strong>. The Bernard Lyot Telesco

Fig. 12. The Bernard Lyot Telescope tower and dome. The cap is open and pointing eastward. The building is located to the south-west of the summit (2013). Photo © Régie du Pic du Midi and Observatoire Midi Pyrénées

In order to take advantage of all the benefits the summit has to offer, the position of the structure was determined by the wind tunnel. This was the first time such a method was used in deciding where to place an astronomical site. Following this analysis, the southwest of the summit was chosen. In order to escape the turbulence caused by the floor heating up during the day, it was decided that the dome should be placed on a tower measuring 28 metres high and 14 metres in diameter. The tower is divided into 5 floors. The first being the alluminure room, mirroring the telescope.

The dome’s characteristic form is explained by Jean Rösch’s desire to minimise the disruptions linked to air exchange between the instrument and the inside/outside air. To do this, Jean Rösch wanted to connect the telescope tube directly to the dome opening, which explains the very small size of the latter. Due to a lack of budget, and a disagreement between the team and future users of the instrument, this technical solution did not turn out well. In order to preserve the quality of the image, engineers applied the solutions adopted in Hawaii to the Observatory telescope: a cooled floor and perforated tube.

This imposing structure was built between 1970 and 1978. The building site proved extremely difficult because of the conditions imposed by the high altitude.

This building is a product from the modern era of astronomy. It means that the Pic du Midi is today a pioneer in stellar (star) magnetism observation and holds an avant-garde place in international research.

<strong>Fig. 13</strong>. The construction of the

Fig. 13. The construction of the dome in 1974. The difficult conditions the mountains are clearly visible: frost covered the buildings and the construction machinery. Photo © Régie du Pic du Midi and Observatoire Midi Pyrénées

Movable heritage objects—telescopes

The first coronograph in the world, invented by Bernard Lyot in 1933

<strong>Fig. 14</strong>. The first coronograph in

Fig. 14. The first coronograph in the world. Invented and tested by Bernard Lyot at the Pic du Midi. It is displayed in the museographic space in the observatory (2013). Photo © Régie du Pic du Midi and Observatoire Midi Pyrénées

 <strong>Fig. 15</strong>. Image from a film of th

Fig. 15. Image from a film of the solar corona taken by the Pic du Midi chronograph in 1935. Photo © Vidéothèque du CNRS

This coronograph was invented and tested during the 1930s. The first films and images of the solar corona were created by Bernard Lyot at the Pic du Midi as early as 1935.

The 60cm telescope (1922)

<strong>Fig. 16</strong>. On the left of the pictu

Fig. 16. On the left of the picture, the 60cm Telescope in 1947. At this time, it was placed under the dome that would house the 1 metre Telescope. Photo © Alix, Fond Eyssalet

The T60 was installed in 1947 at the Pic du Midi. At the time, it was the instrument with the greatest diameter in the observatory. Today, it is the oldest telescope still in working order. In the 1950s, it was used mainly for photometry. With the arrival of the 1 metre Telescope in 1963, the T60 was placed in the smallest dome on the same floor as the terrace and was principally used for the study of extragalactic nebulae. In 1982, the Toulouse Observatory created a committee of amateur and professional astronomers who would manage the new research programmes for the T60. This initiative allowed us to test the participation of amateur astronomers in professional research programmes. Given the success of this initiative, the T60 association was created in 1985. Today, an important associative network supports the association responsible for maintaining and developing the operation of the telescope. Incidentally, it was in the T60 that the first CCD amateur camera was placed in 1985.

 <strong>Fig. 17</strong>. The 60cm Telescope and

Fig. 17. The 60cm Telescope and its modern equipment (2012). Photo © Association T60

The Jean-Rösch telescope (1961)

<strong>Fig. 18</strong>. The Jean Rösch Tele

Fig. 18. The Jean Rösch Telescope 50cm lens (2012). Photo © Observatoire Midi Pyrénées

<strong>Fig. 19</strong>. Plan of the dome and Jea

Fig. 19. Plan of the dome and Jean Rösch Telescope where it can be seen that these two together form one single instrument. Photo © Observatoire Midi Pyrénées

The current Jean Rösch Telescope (JRT) is the result of several years of evolution. Its observation domain is the photosphere (solar surface) in very high resolution. The characteristic of the instrument lies in the originality of its construction. It is directly linked to the structure that protects it: the Tourelle dome. It is the combination of the telescope and dome, as it were, which form the real instrument. We have already spoken about the Tourelle in the previous section, therefore here, we will present the quality of the optics, instrumentation, and results obtained: the best images of the solar surface taken from the ground.

The JRT was initially equipped with a 38cm lens; in 1972, Jean Rösch received supplementary funds in order to increase the strength of the lens. A 50cm lens was fashioned in the Observatory in Paris by Jean Texereau. This lens is today considered the masterpiece of the optician’s career. Up until 1987 (the beginning of the La Palma Telescope), the JRT was associated with the atmospheric qualities of the Pic du Midi; in fact it was the best performing instrument used to observe the sun in the world.

The research carried out by the JRT in the 1970s had an important impact on the evolution of solar physics, especially on the interaction between granulation and the cycles of solar activity.

The JRT is today part of an international solar observation network, on ground and in space. The largest instrumentation field of the telescope has no competition for the time being, which allows it to remain complementary to major international space observatories.

The 1 metre Telescope (1962)

As with the JRT, the T1M benefitted from several optic and instrumental improvements over the course of its history. NASA encouraged its construction in 1959 because of a desire to increase the instrumental power of the Manchester Lunar Programme and thus obtain the best possible images of the moon for the Apollo Programme Lunar Atlas. In 1974, the old optic was replaced by a new Pyrex mirror built by Jean Texereau, one made from a material which is not too sensitive to heat.

For the telescope’s first ten years of service, it was used the opposite way round (from that expected) as a transmitter/receiver of light. A network of great scientific institutions created a project (Ecole Polytechnique, CNES, CNRS) whose goal was to measure the distance between the Earth and the moon in laser shots. The first echoes were measured in 1969 following the placing of reflector panels on the moon by Apollo 11.

The T1M is today equipped with a CCD camera and is managed by the Institut de Mécanique Céleste et de Calcul des Ephémérides in the Paris Observatory. It is designed to study the planets and small bodies of the solar system.

<strong>Fig. 20</strong>. The 106 cm Telescope in

Fig. 20. The 106 cm Telescope in the 1950s. It is equipped with material for silver shots using its cassegrain focus. Photo © Observatoire Midi Pyrénées

The Bernard Lyot 203cm Telescope (1976)

 <strong>Fig. 21</strong>. View of the interior of

Fig. 21. View of the interior of the Bernard Lyot Telescope dome. The red structure is the horseshoe-shaped setting which supports the 2 metre telescope. The NARVAL system can be seen, installed at the telescope’s focus (2009). Photo © Paul Compère

<strong>Fig. 22</strong>. Model of the magnetic fi

Fig. 22. Model of the magnetic field of Star SU Aurigae, created using the NARVAL and ESPADON systems (2007). Photo © Observatoire Midi Pyrénées

The Bernard Lyot Telescope is described by its founders as the greatest achievement of the human and scientific adventure at the Pic du Midi. Even though the difficulties met during its development and creation meant the initial project could not be carried out, the Bernard Lyot Telescope remains today the most important telescope on French soil and holds a singular place on an international scale.

The double focus telescope (cassegrain focus open at f/25 and strand at f/5) is installed on a 16-ton horseshoe-shaped structure resting on an oil bath.

During the first thirty years of its service, the BLT was a generalist instrument used to serve the international astronomical community (infrared-visible imagery, photometry, polarmetry, spectroscopy). In 2006, the BLT was equipped with a spectro-polarimetre, named NARVAL, installed on a network with the Canada-France-Hawaï Telescope for continous monitoring.

Thanks to NARVAL and the BLT, the Pic du Midi Observatory has become the current most important contributor in the study of stellar magnetism. Among its key findings, we can mention the characterisation of the magnetic field of several stars (small and massive), the inversion of the magnetic field in several stars and so forth.

Finally, it is important to note that the BLT was one of the main factors that led astronomers and public workers to initiate the Pic 2000 project and thus save the scientific work of the observatory.

Movable heritage objects—small instruments, books, archives and photographs

<strong>Fig. 23</strong>. Extracts from the invent

Fig. 23. Extracts from the inventories of the Pic du Midi’s heritage objects. Images: Ramond Society Heritage Fund in Bagnères de Bigorre. Photo © Société Ramond

All small items, books, archives and photographs related to the Pic du Midi are preserved in various heritage collections and are currently undergoing an inventory.

Several different structures share these pieces of heritage: The National Centre for Scientific Research (CNRS), The Observatoire de Paris, the Heritage Commission of the Midi Pyrenees Observatory, the Departmental Archives of Tarbes, the Ramond Society Heritage Fund in Bagnères de Bigorre, and the Eyssalet Photography Fund which is part of the Haute-Bigorre Community of Communes.

A common fund is being created in order to bring these iconic pieces of heritage together and thus display them in the museum area of the Pic du Midi.


History and development 
  • InfoTheme: Astronomy from the Renaissance to the mid-twentieth century
    Entity: 76
    Subentity: 2
    Version: 81
    Status: PUB
    Date: 2017-05-17 17:05:41
    Author(s): Nicolas Bourgeois

140 years of life and science in the high mountains

 <strong>Fig. 24</strong>. The Plantade station on

Fig. 24. The Plantade station on the Col de Sencours in 1875. The summit of the Pic du Midi in the background is still devoid of any development. Photo © Alex, Fond Eyssalet

<strong>Fig. 25</strong>. The same view as in Fig.

Fig. 25. The same view as in Fig. 24, in 2013. The Plantade station, currently in ruins and undergoing rennovation. 140 years later, the most important working observatory in France stands on the summit of the Pic du Midi. Photo © Nicolas Bourgeois

The history and development of the Pic du Midi Observatory are primarily guided by three ideas.

The first is a contemporary mountain approach which asserted itself in the 19th century. For members of the Ramond Society, founders of the Observatory, the Pyrenees are a world created to defy temerity, elevate the soul, explore and discover. This culture may explain in part the many risks taken for the good of the observatory.

The second is that the Pic du Midi, by its very geographical position and its atmospheric quality, has seen itself become a centre for research and a science hub. Even if astronomy later became an important uncontested element, science itself has reigned for over 60 years. And we must not forget that the observatory is also a scientific platform where various different domains of research are carried out: meteorology, climatology, cosmic rays, botany, medicine... This led to the significant development of the Pic’s infrastructure in order to meet the influx and expectations of a growing number of increasingly diverse researchers.

Finally, the Pic has always been threatened. Whether by the ever difficult mountaineering conditions, budget constraints or competition from major international observatories, the growing threat of closure is very real indeed. But the Pic has always resisted. From the first stakeholders, to the scientists and finally the elected officials, there has been a chain of supporters and a human adventure continuously upholding this threatened heritage.

We will address the Pic du Midi’s history in six periods, through the facts, events and the scientific work. Details of dates, facts and scientific results will be accompanied by a mention of the key people that shaped the Pic and built its history.

<strong>Fig. 26</strong>. The men’s ongoing batt

Fig. 26. The men’s ongoing battle on the summit during the winter of 1908. Photo © Régie du Pic du Midi and Observatoire Midi Pyrénées

From Genesis to the first stone (1865-1891)

The question of building an observatory on the summit of the Pic du Midi arose in the eighteenth century. But it was in the mid-nineteenth century that the project really started to take shape thanks to members of a newly formed Pyrenean company: Ramond Society. Its founders define it as a Pyrenean exploration company, grouping together scientists and mountaineers. For these men, the Pic du Midi would be the perfect host for a high quality observatory. France learned about the impending creation of the observatory in 1869 via the Official Journal.

The war of 1870 caused the project to be suspended, then two years later, added weight to the argument that the work should restart: indeed in a country bruised by defeat, the observatory presented a way of raising the morale of the French people.

Two men will forever mark the history of the Pic du Midi. This is because they are at once the founders of the observatory and the guarantors of its Pyreniste identity. They are the General Charles Champion du Bois de Nanssouty and the engineer Célestin-Xavier Vaussenat.

Thanks to their efforts and research grant, the Pic du Midi project was voted in on 8 April 1873 and it was executed on 21 May 1878. Thirty workers worked on the summit until 1881, under the direction of General Nanssouty’s wife, Lucie Abadie.

On 27 July 1882, Vaussenat and Nanssouty donated the observatory to the French State in order to ensure its management, obtain finance and reimburse the debts. Xavier Vaussenat died on 16 December 1891, a date which marks the end of the first period in the history of the Pic du Midi.

Scientific work and results

During this period, the Pic du Midi was the centre for many experiments and meteorological readings, in particular for the central weather bureau.

Many of these experiments proved and presaged the quality of the observations which would be able to be carried out.

The first decade of the Pic du Midi Observatory was thus a period of material expansion. Vaussenat, as well as setting up and securing the site, also contributed to publicising the summit by inviting scholars there during the summer period.


In 1882, the observatory was made up of a house (the Nanssouty building), which joined a small building by a narrow path (the future Vaussenat building), leaning against a blockhouse where the weather instruments were installed.

A blacksmith’s, a stable and some shops were also installed on the summit.

Celestin Vaussenat, up until his death, sought to level out the peak and build sheltered passages to facilitate travel in winter, when snow covers the station.

Work at this time is only possible three months a year, from July to September, when there is no snow on the summit and the caravans and mules can access the top and get back to work.

<strong>Fig. 27</strong>. The Pic du Midi Observat

Fig. 27. The Pic du Midi Observatory in 1891. From left to right; the blockhouse, the Vaussenat building and the Nanssouty building. The construction of the terrace had not yet begun. Photo © Régie du Pic du Midi and Observatoire Midi Pyrénées

Systematic observations and the trials of the First World War (1892-1920)

From the arrival of the new director Emile Marchand in 1892 onward, the Pic gradually became a centre of multidisciplinary scientific observations, for which data in meteorology, atmospheric physics, seismology, astronomy and botany would be collected daily.

<strong>Fig. 28</strong>. The men from the infantr

Fig. 28. The men from the infantry regiment in Tarbes carrying the Baillaud Telescope materials up to the summit (1906). Photo © Régie du Pic du Midi and Observatoire Midi Pyrénées

In 1900, the Pic saw the arrival of the Toulouse Observatory and its director, Benjamin Baillaud, who would encourage the building of the first dome and its grand telescope.

The Pic du Midi had a hard time during the First World War (1914-1918). Emile Marchand died in 1914 and so the Pic found itself with no director, no maintenance - a state of abandonment from which it only insecurely emerged in 1920 with the arrival of its third director, Camille Dauzère.

From 1903 to 1908, the main stages of construction of the first astronomical observatory of the Pic du Midi took shape. In 1906, the dome was built on the summit. Then the 50 cm Telescope, built in a Parisian workshop, was brought by rail to Bagnères, then by oxen and cart to the Col du Tourmalet. From there, a dozen soldiers of an artillery regiment from Tarbes, were to persevere for more than a year to get the 22 boxes of material up to the summit.

In September 1907, the telescope was atop the Pic; another summer would be required to assemble it and make it operational. During the first 20 years of its use, the astronomical observatory held a place that was both paradoxical and representative of the Pic du Midi’s history. The observations made there were considered to be excellent. But the conditions faced by the observers (cold, snow, difficult access, temperamental weather), were such that motivated astronomers were rare indeed. The telescope remained practically unused until the 1930s.

Scientific work and results

During the 22 years of his direction, Emile Marchand collected with his teams a considerable number of daily measurements: the map of the Sun, planetary surfaces and cloud cover, meteorological recordings, atmospheric electricity, terrestrial magnetism and seismology.

During this time, Marchand published 35 articles on geophysics, 20 on astronomy, 9 on botany and 6 on the relationship between the Sun and the Earth. Unfortunately, most of the articles reached only the local society review and congress reports.

Nevertheless, we must go beyond the "anonymous" nature of these results, in order to see the emerging intensity of observation at the Pic du Midi, prefiguring its arrival at true scientific maturity from 1920 onwards.

The thirty years described here mark a new complexity and intensity in the history of the Pic du Midi. The observatory gained a paradoxical reputation. It fascinated people with its size and potential, as much as it pushed people away with the tough conditions it imposed on men and observations.

Infrastructure: Landscaping, development of means of observation, construction of the Baillaud observatory building

Before the First World War, the main construction efforts were turned towards increasing the effective surface area of the Observatory and the development of instrumental means..

The greatest additions to the Pic du Midi’s infrastructure at this time were the installation of the astronomical observatory in 1908, with the Baillaud Dome, the 50cm Telescope and a building for accommodating astronomers.

<strong>Fig. 29</strong>. The Pic du Midi Observat

Fig. 29. The Pic du Midi Observatory just after the First World War. We can see the Baillaud dome and observatory building on the right, built between 1906 and 1908. The north terrace crumbled following several years without maintenance (1920). Photo © Régie du Pic du Midi and Observatoire Midi Pyrénées

The ’Dauzère years‘, the first real threats for the Pic and scientific maturity (1920-1937)

Camille Dauzère was appointed Deputy Director by Toulouse on 31 August 1920. Under his leadership, the Pic’s strong, symbolic identity materialises, that which gives it the power of resistance. Only just out of the First World War, the Observatory experienced its first major crisis. The platform was in a fragile state and its future greatly threatened by a report of the inspection of French observatories in 1922.

Against all the odds, these vulnerabilities and threats were a blessing to Camille Dauzère. They raised great support from the public, local elected officials and the people in charge of the Pic. This large mobilisation provided substantial funds to the observatory, which would be renovated and expanded, over fifteen years.

Under Dauzère, the Pic’s research assured its position and became internationalised. From 1920 to 1935, geophysics and meteorology were the queens of sciences.

Astronomy was still a rather secondary element until the arrival and intervention of several important figures in and after 1930. Those figures firmly pushed the Pic towards the stars for the following 60 years.

From 1930 to 1937, astronomy made its progressive comeback. Bernard Lyot, astronomer at the Paris Observatory, made the most of the transparent sky above the Pic du Midi in order to develop the first coronograph in the world. A few years later, the first images of the solar corona were producing under the Baillaud dome.

Scientific work and results

From 1920 to 1935, the Pic du Midi acquired a certain maturity and an international reputation in terms of scientific research. It was to geophysics that the Observatory owed its reputation.

Joseph Devaux, meteorologist, produced his thesis on the thermal assessment of snowfields and glaciers. Camille Dauzère, interested in both lightning and hail, completed and put to good use a remarkable database on the impact lightning made on the summit.

The reputation Camille Dauzère acquired for this work strengthened his conviction in building a terrestrial physics laboratory on the summit.

The ’Dauzère years‘ revealed the symbolic and mythical dimension of the Pic du Midi. Cornered, the observatory raised awareness and goodwill while preparing for its own renewal. The summit showed, despite its wild location, that it was a great observation site, allowing for both versatility and excellence. At the end of the Dauzère era, all the conditions were met to be able to plan and fund the major projects of the Pic du Midi.

Infrastructure: Modernisation of communication and construction means for Terrestrial Physics

  • 1926: installation of the T.S.F. Two 25-metre pylons were built on the Pic for broadcasting. The Observatory gradually emerges from its isolation.
  • From 1926 to 1933, a route was constructed between the Col du Tourmalet and the Col de Sencours, which continued until Laquet, allowing for easier transport of men and materials. A hotel was to be built as the end of this road.
  • 1928 to 1936 saw the drawn-out construction of the Terrestrial Physics laboratory called the Dauzère building, which would become the future host of the Pic’s laboratories and the 1 m Telescope.

<strong>Fig. 30</strong>. The Pic du Midi Observat

Fig. 30. The Pic du Midi Observatory in 1925. The two TSF aerials have been placed on the summit. The crumbling northern ravine started to be reinforced. Photo © Alix, Fond Eyssalet

The major projects (1937-1947)

Jules Baillaud, director of the Paris Observatory, succeeded Camille Dauzère in 1937. He devoted his directorship to the planning of the Observatory’s major projects.

Jules Baillaud was very aware of the great difficulties imposed by the Pic on scientists who, inevitably, emphasised its fragile situation when faced with councillors and national astronomers. His priority pre-war was to take on an ambitious renovation programme to make life easier on site: the building of a cable car to revolutionise access, and finally the installation of a power line to resolve energy problems. "The Baillaud Decade" brought the foundations for the observatory to enter the modern era.

<strong>Fig. 31</strong>. The refracto-reflector,

Fig. 31. The refracto-reflector, named the Baillaud Telescope, under the Baillaud dome in 1947. It was with this instrument that the main planetary and solar observations from 1950-60 were made. The instrument was dismantled in 1970 and replaced by a coronograph. Photo © Régie du Pic du Midi and Observatoire Midi Pyrénées

Bernard Lyot, astronomer at the Paris Observatory, supported Jules Baillaud in his astronomical projects. It is to him that they owe their original and audacious character.

In 1942, a new 60cm optic was installed on the Pic. The large 18 metre focus folds up on itself, transforming the telescope into a refracto-reflector. Rechristened the "Baillaud Telescope", this instrument was used with a great deal of success in the 1960s and would become the instrumental flagship of the Pic.

After the war, the main projects that had been prepared by Jules Baillaud and catalysed by Bernard Lyot would finally be completed. The rise and influence of the Pic du Midi could begin.

Infrastructure: Renovation of the first buildings and completion of the Dauzère building

  • 1937: The Nanssouty building was renovated and received a new roof: a reinforced concrete vault. This roof would be more resistant to the conditions experienced on the summit (the weight of the snow and the violent winds are still present today).
  • 1946: The wealthy amateur astronomer Marcel Gentili gave the observatory a dome (the future dome of the 1 m Telescope) and a 60 cm telescope, in order to thank its members for hiding him from the Nazis during the war. The new dome was installed on the Dauéère building whose construction began in 1935 and was completed in 1948.
  • 1947: The observatory is connected to La Mongie by a cable car exclusively reserved for transporting equipment. The arrival point of the cable car is located southwest of the Baillaud dome.

<strong>Fig. 32</strong>. The Pic du Midi Observat

Fig. 32. The Pic du Midi Observatory in 1948. We can see the extension of the Dauzère building to the left of the image, the installing of the Gentili dome, and the Nanssouty building’s new roof. Photo © Yan, Fond Eyssalet

The rise of astronomy and the international influence of the observatory (1947-1981)

Jean Rösch, an instrumentalist astronomer, was director of the Pic du Midi over the course of these prosperous years. In order to describe this long period of direction, he divided it into three parts:

  • 1947 to 1952: The major infrastructure work and arrival of the cosmic ray specialists.
  • 1953 to 1964, the decade following the building of the cable car, was the phase of all-round expansion of scientific work and the internationalisation of the Pic du Midi’s reputation.
  • 1965 to 1981, saw the proposed increase in instrumental power of the observatory with the 2m Telescope, Jean Rösch’s largest investment.

The ’Rösch years‘ fundamentally break with the observatory’s first 50 years. There has been a surge in all its components: the personnel, infrastructure, instrumental means, and scientific topics.

The major infrastructure work and arrival of the cosmic ray specialists (1947-1952)

The arrival of the cosmic ray specialists from Manchester in 1949 fused the revolution of the observatory. Their presence, their needs and the results of their work allowed Jean Rösch to boost all the major infrastructure projects that would transform the Pic forever. Indeed, they needed a means of transportation to bring their electro-magnet to the summit and a high-powered electric current to operate it.

 <strong>Fig. 33</strong>. Construction of the fir

Fig. 33. Construction of the first cable car station on the south side of the Observatory. 1950. Photo © Alix, Fond Eyssalet

On 15 August 1952, the real revolution for the Pic began: the first cable car docked at 2,877 metres above sea-level. This event brought about the need for intensive development of the infrastructure in order to accommodate the increase in personnel and meet the expectations of the researchers.

Scientific work and results

In 1950, a new particle was discovered at the Pic by the cosmic ray specialists from Manchester. It was named ’Hypéron‘ during the International Congress of Cosmic Rays in Bagnères de Bigorre in 1953. This discovery was rewarded with a Nobel Prize.

Infrastructure: Major works as the Pic du Midi enters the modern era

<strong>Fig. 34</strong>. The first Pic du Midi ca

Fig. 34. The first Pic du Midi cable car, the symbol of its entry into modernity. 1952. Photo © Alix, Fond Eyssalet

  • Between 1945 and 1949, the high tension line was built. This 10,000-volt line came into service on 18 November 1949. The unlimited electrical current attracted many heavy usage experiments. The supporting cable greatly facilitated building extension work.
  • in June 1949, a funicular was built in order to connect the hotel in Laquet to the observatory. The installation of this framework on the incline was justified by the Manchester cosmic ray specialists’ need to transport the electro-magnet. The series of mules that had been marching up the Pic du Midi for 75 years disappeared forever.
  • On 15 August 1952, the real revolution for the peak began: the first cable car docked at 2,877 metres above sea level. The observatory emerged out of isolation for good bringing with it a complete development of the infrastructure which would accommodate the increase in personnel and meet the expectations of the researchers.

All-round expansion of scientific work and the internationalisation of the Pic du Midi’s reputation (1953-1964)

From this period on, the scientific work is such that it becomes the main factor in the history and development of the Pic du Midi. The facts and events in this section will therefore be explained in terms of scientific work.

Scientific work and results

The cosmic rays decade (1949-1959)

Throughout these ten years, several internationally renowned teams brought advanced experiments on cosmic rays to the Pic. Priority was given to high altitude observatories at this time because they attenuate the destructive effect of the atmosphere on these particles. What’s more, interest in cosmic rays increased after the 1950s. Indeed, their study provided an indirect way to do nuclear physics. The cosmic ray specialists at the Pic can be separated into two categories.

The Manchester team was joined in 1951 by others from the Polytechnic School, led by Louis Leprince-Ringuet. In 1951 he installed equipment that performed better than the Manchester team’s equipment on the summit. According to Leprince-Ringuet, the Wilson Chamber installed on the summit was the biggest of its kind worldwide. With this instrumentation, they discovered new particles in subatomic matter, which earned them the Cognac-Jay Prize from the Academy of Sciences in 1962. In 1959 and 1960, the accelerators of CERN and Brookhaven resulted in the polytechnicians leaving the Pic.

The Sun

Monitoring of the solar corona with the Lyot coronograph in the 1930s was both the starting point and catalyst for research undertaken at the Pic sur le Soleil in the second half of the 20th century.

Jean Rösch equipped the observatory building with new instruments in order to study the solar atmosphere in its entirety. Alongside the solar corona, it was now possible to study the photosphere and the chromoshpere. This work and its potential, attracted many scientists: Lyot’s "heirs" at the Meudon Observatory and foreign researchers.

In 1955, the study of solar granulation was at the top of global scientific research on the Sun and the photographs from the Pic were considered the best available. Up until 1987, when the La Palma Telescope arrived in the Canary Islands, the Pic du Midi was the most important solar observation site in the world.

The Moon

The infrastructure and high quality images of the Pic, secured its selection in 1956 to carry out the "Manchester Lunar Programme". In 1959, thousands of lunar images taken at the summit, impressed the US Air Force so much that they decided to fund the observatory to map the Moon. This work contributed directly to the Apollo programme launched in 1961. Placed under American management, the mapping of the Moon required the work of more than 50 people at the Pic. In 1964, a 1 metre telescope, funded in part by NASA, was installed under the Gentili dome and took on the Baillaud Telescope for lunar observations. The American Orbiter probes 1-5 were launched between 1966 and 1967, and marked the decline of the "Manchester Lunar Programme".

The planets and their satellites

As with the Sun and Moon, the quality of the research and planetary images have contributed to the worldwide reputation of the Pic du Midi. The intense development of planetary exploration in the 1950s and 60s was mainly due to Andoin Dolfus.

Mars was the subject of detailed cartography for more than a decade. Henri Camichel was able to determine the length of day, the diameter, the levelling of the planet, the pole alignment and the orientation of its rotation axis with great accuracy.

The exploration of Saturn at the Pic also provided important contributions to planetary science. In 1966, Andoin Dolfus was involved in the discovery of one of the outer rings of the planet, as well as that of one of its small satellites, which he proposed to name Janus.

Venus was also the target of many observations. The work conducted by Andoin Dolfus helped highlight the retrograde rotation of the Venusian atmosphere. This four-day hyperotation, confirmed in 1972 by the Mariner 10 probe, was considered to be one of the most important discoveries to which the Pic du Midi has contributed.

The study of the planets’ soil, atmosphere and their satellites is the most original contribution that the Pic has made in the field of planetary science. By using a polarimeter, an instrument rarely used at that time, Andoin Dolfus was able to deduce the composition of planetary surfaces, notably those of Mars and of the Galilean satellites. Results on the Galilean satellites were confirmed in the 1970s by the Voyager probes.

The 1970s heralded the era of such space probes, and thus the planetary research at the Pic gradually reduced - research which had been hitherto considered unrivalled.

Infrastructure: Expansion in response to the intensification and diversification of scientific and technical demands

Work on the infrastructure at the beginning of the 1950s and the observatory’s increase in power, led to the extension and construction of several buildings. The Marchand Laboratory was built in 1956, the Labardens building completed in 1957.

<strong>Fig. 35</strong>. Aerial view of the Obser

Fig. 35. Aerial view of the Observatory in 1960. The western part of the summit is not yet taken up with the interdepartmental building. In the centre, we can see the new cable car station at the top. Photo © La Pie servie aérien


  • On 15 February 1961, the Tourelle Dome was inaugurated, installed on the eastern part of the platform.
  • 1962-1963: The summit welcomes the structure which today makes it recognisable to all: the interdepartmental building with its 103 metre high aerial. These buildings are not part of the Observatory and handle services related to broadcasting, civil and military communications. It should be noted that the astronomers’ influence was such at the time that they succeeded in banning the installation of a light on the aerial which rises to over 3,000 metres above sea level.
  • 1964: The 1m Telescope, financed by NASA, was placed in the Gentili dome. The Pic du Midi’s great nocturnal telescope era began here.

<strong>Fig. 36</strong>. The face of the Pic du M

Fig. 36. The face of the Pic du Midi changes for good with the arrival of the 103 metre-high aerial and the interdepartmental building (1963). Photo © Alix, Fond Eyssalet

The increase in instrumental power of the observatory (1965-1981)

In 1965, John Rösch began the 2m telescope project in order to afford the Pic its place in an astronomical context where the reputation of an observatory depends on the power of its instruments. This also served to make the most of the conditions offered by the summit.

The BLT, built from 1970 to 1981, is available to the international community. As the largest national telescope, for several years it was used as one of the tools in an immense research strategy in a multitude of projects across a range of topics.

The John Rösch years marked the highest point in the history of the Observatory. During these three decades, the Pic was consistently placed at the forefront of various themed astronomical observations and contributed hugely to scientific progress in this area.

The years 1970 and 1980 marked a set of technological and international revolutions to which the Pic has tried to adapt. It gradually yielded to the space probes and the giant international and spatial telescopes. Nevertheless, the Pic du Midi’s scientific and resistive core carries on, the Bernard Lyot Telescope demonstrates this.


  • 1970-1981: the construction of the Bernard Lyot Telescope and its observatory building makes up the last phase of the scientific infrastructure development on the summit. The first landscaping work began in 1970, the building was completed in 1976 and the telescope was fully operational in 1981. The construction of the BLT and the aerial are the most important and iconic features of the Pic du Midi.

<strong>Fig. 37</strong>. Aerial view of the Pic d

Fig. 37. Aerial view of the Pic du Midi Observatory in 1990. The scientific infrastructure is at its height before the reconfigurations during the 2000s. Photo © Régie du Pic du Midi and Observatoire Midi Pyrénées

The dark years to come (1982-2000)

Throughout the 1980s, France reorientated its astronomical policy in order to prepare for the advent of major international observatories like the VLT. The development of these projects required transforming the management and financing of national observatories. As with the crisis of the 1920s, the continued functionning of the observatory was deemed too expensive and its closure was announced for 1998.

In 1993, the new director Michel Blanc, presented the "Pic 2000" project. This project was a challenge of reconfiguration: positioning the Pic du Midi on a new technology-oriented university campus and redeveloping the site in order to sustain the scientific work at the summit whilst opening it up to tourism.

In 1993, a public coalition was set up. The Syndicat Mixte for tourism development at the Pic du Midi was created. A set of public and private partners came forward to help fund what would become the highest construction site in Europe, the work starting in 1996.

In June 2000, the Pic opened its doors to tourism. Consequently, its 100,000 visitors a year would allow the Pic to take on its own operating expenses and continue its scientific work. The observatory has since been asked to develop both these aspects. The touristic activity must reinvent and enrich itself while always preserving the identity and integrity of the site. The scientific work, meanwhile, should be situated in specific fields and excel at these on an international level.

 <strong>Fig. 38</strong>. Since 2007, the Pic du

Fig. 38. Since 2007, the Pic du Midi has been opening its doors to tourists at night for evenings dedicated to observation and the discovery of the observatory. The astronomers and facilitators enhance the public experience (2014). Photo © Nicolas Bourgeois

Scientific work and results

Even during the dark years of the Pic 2000 project, the astronomical work never stopped. From 1980 to 2000, the BLT was a universal telescope, available to the international community. From the year 2000 onward, the instrumentation and investigation fields of the BLT were rationalised in order to keep its place on the world astronomy scale. In 2007, the telescope became specialised in stellar spectro-polarimetry using its NARVAL system. This was such a new field of study that the only telescopes practising it were the BLT in collaboration with the France Hawaii Telescope.

Alongside the BLT, other telescopes carried on their observation programme. The 1 metre Telescope was operated by the Institute of Celestial Mechanics and Ephemeris Computation in Paris (Institut de Mécanique Céleste et de Calcul des Ephémérides: MCCE). It specialises in monitoring planetary surface and the study of small solar system bodies. The Rösch Telescope and Tourrelle dome were managed by the PMO and were used specifically for the training of PhD students in astrophysics for observing the photosphere. The continued monitoring of the solar corona was ensured via instrumentation and infrastructure recently installed for the Pic 2000 project. The observers and monitoring were entirely funded by sponsorship.

With the Pic 2000 project, the PMO was able to expand the range and direction of the Pic’s fields of research; among them, atmospheric sciences. The observatory contributed to the study of atmospheric pollution and transient luminous phenomena.


<strong>Fig. 39</strong>. The new cable car statio

Fig. 39. The new cable car station at the summit and the high-capacity cable car (2000). Photo © Régie du Pic du Midi and Observatoire Midi Pyrénées

<strong>Fig. 40</strong>. The Pic du Midi Museogra

Fig. 40. The Pic du Midi Museographic space, telling the Observatory’s scientific and human history (2005). Photo © Régie du Pic du Midi and Observatoire Midi Pyrénées

The latest work on the Pic du Midi’s infrastructure was done in order to accommodate tourism whilst preserving the scientific work. This was all done between 1996 and 2000.

  • Installation of a high capacity cable car (300 people/ hour).
  • Reconfiguration of the platform with the installation of different infrastructures and services dedicated to tourists: a museographic space in the Baillaud dome buildings to display 140 years of life and science atop the Pic du Midi; a restaurant to accommodate 80; facilities to manage the flow of people, safety and movement on the terraces; refurbishment of all rooms and premises.
  • Installation of a new coronograph observatory building on the south east terrace.

<strong>Fig. 41</strong>. The new dome and coronog

Fig. 41. The new dome and coronograph ensuring continuous monitoring of the solar corona (2008). Photo © Régie du Pic du Midi and Observatoire Midi Pyrénées


Justification for inscription

Comparative analysis 
  • InfoTheme: Astronomy from the Renaissance to the mid-twentieth century
    Entity: 76
    Subentity: 2
    Version: 3
    Status: PUB
    Date: 2015-02-12 09:19:57
    Author(s): Nicolas Bourgeois

The Pic du Midi’s profile is unique in the great family of worldwide scientific observation stations. Firstly, its history is rooted in the early development of the application of scientific method to nature in the seventeenth century. It is one of the last high-altitude resorts built in the nineteenth century that is still used as a window on the geophysical and astrophysical universe. This vibrant site has witnessed evidence of the human desire to gain knowledge in fields as diverse as meteorology, aerology, botany, geophysics, astronomy, and particle physics over the years of its existence.

There are a fair number of observation stations at altitude in the world, but the stations in the high mountains can be counted on one hand. The Alpine station, Jungfraujoch in Switzerland, is the last one still open, and the Californian observatories, amongst some of the oldest, are not in the high mountains. Even the great Andean astronomical observatories are recent.

Indeed the scientific work of all these sites is dedicated to a particular subject area (aerology for Jungfraujoch, astronomy for the others), or it is being severely compromised by adjacent human activities (as is the case for Mount Palomar and all the observatories in urban and periurban areas).

The major active sites, the island observatories (Hawaii and the Canary Islands) and the astronomical sites in the Chilean Andes (VLT, La Silla, CTIO, ALMA), all have a relatively recent history (starting in the 1970s for the oldest ones and the 2000s for the more recent) and thus do not convey the feeling of exceptional human adventure and closeness to the historical roots of scientific exploration that is found at the Pic du Midi.

The Pic du Midi uniquely illustrates the power of humanity. Thanks to the perseverance of men and women from diverse origins (rich sponsors, Pyrenean mountain enthusiasts, believing scientists, shepherds from the valley who love their mountain), all with a variety of reasons, but driven by the same enthusiasm, the Pic du Midi has become and will continue to be a space where culture, science and art cross paths and complement one another by making the unspoilt beauty of the site and landscape available to everyone.


Integrity and/or authenticity 
  • InfoTheme: Astronomy from the Renaissance to the mid-twentieth century
    Entity: 76
    Subentity: 2
    Version: 7
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The integrity of composition is satisfactory because all major historical activities are present (foundations of the early twentieth century, historic domes, etc.), or represented on the Pic du Midi’s site and its surroundings (buildings with nineteenth century origins, historical paths, etc.), by correctly identified material evidence. It is therefore possible for the visitor to have a clear enough idea about the past and present of the site.

The structural integrity of today truly represents the overlapping and correlation of functions historically assigned to the Pic. These activities have been continued since the founding of the observatory, and the renewal of individual components in accordance with new requirements has always been done in keeping with the original elements.

The functional integrity is marked by the fact that the Pic’s various main activities have been in harmony with one another right from the beginning and they have always complemented one another and been organised around the Astronomical Observatory: scientific observations of the sky and the atmosphere, welcoming and lodging of tourists and mountaineers, broadcasting functions. The buildings and infrastructures form a whole which serves the well being of the Pic so that it may continue in its original, historical role.

The quality of the panorama and the night sky are such that the celestial landscape integrity of the Pic du Midi reflects one of the most remarkable, natural properties of the site. The origin of this lies as much in its vocation as a scientific station at altitude as with its popularity and tourist success (pyreneism, mountaineering, snow sports, visiting for the view, amateur astronomy, etc.). The conservation of this double integrity, both night and day, today makes up one of the major challenges for the conservation of the site.


Whilst the Pic du Midi’s qualities of integrity can be considered comprehensive and sometimes of an exceptional standard, its authenticity provides more complex elements to enjoy.

The authenticity of its design has been based on a continuity of real estate, scientific and civil engineering initiatives since the first projects came into being towards the end of the nineteenth century. They can only be understood within the dynamic of the site and the renewal of techniques in order to benefit site development: creation of domes and scientific instruments, current evolution, creation of cable car access, construction of the great broadcasting tower, and so on.

The authenticity of the components and materials is also based on this new dynamic, specific to a scientific station which has had multiple purposes throughout its history: introduction of reinforced concrete, progress in dome construction, evolution of architectural structures. A specific feature marking this dimension of authenticity is the respect for existing buildings and the sympathetic superimposition of new structures on the older ones. This has been especially true since the equipment of the early twentieth century was installed on the summit - all levels of assembled and historic scientific equipment are present.

The architectural and landscape authenticity is an open subject, and one that only has meaning through the understanding of other closely complementary aspects: that is the understanding of a scientific and touristic place which is continously taking on new forms. It is not possible to judge the authenticity of such a place in the light of classical monuments and heritage sites. The renewal of equipment and the framework of both the scientific and touristic resorts has always been done in a spirit of restructuring the old and two main components have marked a split:

  • the construction of the cable car (1950–1952), which totally changed the access to the Pic and allowed for the site to welcome in the public and remain open all year;
  • the construction of the DFT tower (1953) in the second half of the twentieth century which gave the Pic its visual signature as seen from the valley or the nearby mountain.

There is therefore a visual authenticity of the property that has evolved alongside its accompanying story. What seems important is the perceived authenticity of the Pic du Midi: today, the newcomer’s first strong impression while riding the cable car is that of an authentic and original scientific mountain station authentic. One could even say that the image given by the Pic, with its broadcasting tower surrounded by observatory domes, forms the ideal model and symbol of the high altitude Observatory.

The environmental authenticity is one of the great values of the property, directly linked to the quality of its atmosphere and its clear skies. These values are at the very origin of the Pyrenees and the romantic appreciation of their outstanding tonal range compared to other major European mountain ranges. This was the result of their first foreign visitors, notably British and local elites behind the proposed observatory at the Pic du Midi (see history). It sparked the notion that we should have a seasonal and then permanent presence of man on the Pic, enabling high quality astronomical observations (the role of the Paris Observatory’s substitute, in partnership with NASA). They finally allowed the development of tourism dedicated largely to the Pyrenean panorama, and more recently to the appreciation of its night sky. The preservation of panoramas, for a long period and at the highest level of French legislation (see managing the property: protection and landscape buffer zone) and more recently a major initiative of protecting from light pollution (International Dark Sky Reserve project, 2009–2013), the largest in France to date, guaranteeing the high degree of environmental authenticity and its future protection.


Criteria under which inscription might be proposed 
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  • Criterion (ii): In the history of its construction and development, the Pic du Midi is primarily a national programme that includes important human, scientific and financial means, on both a regional and national level. Through the quality of its night sky, the Pic is the relay and substitute for the Paris Observatory, itself a leader and promoter of very important international scientific programmes (see thematic study on the Paris Obersvatory, same publication). From the 1930s and especially during the second half of the 20th century, the Pic du Midi Observatory developed international character and collaborations in astronomy. It is in particular an observation centre associated with NASA and the spatial conquests (in the 60s).

  • Criterion (iv): The Pic du Midi today represents the ideal model and symbol of a high mountain observatory. It belongs to the older generation of such observatories, designed and built towards the end of the nineteenth century. Over time it has gradually changed its use and today offers a real landscape and cultural icon, visible from far away, showing both the presence of man in altitude and the scientific use of the high mountains. The quality of its climate and atmospheric environment gives its daytime view and exceptional night sky, values that founded its scientific value as much as its touristic reputation.


Suggested statement of OUV 
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In terms of UNESCO categories, it seems reasonable to consider "Cultural Landscape" for the Pic du Midi. This would fit well with the value assigned to the site, its situation as a mountain peak, its general shape as symbolic value and it is consistent with two very important environmental values: a view of the central chain of the truly remarkable Pyrenees by day, and an equally outstanding situation by night due to the quality of the night sky.

The "Outstanding Universal Value" (OUV) is based on the following points:

  • the Pic is a high mountain observatory amongst some of the oldest (important comparative analysis on this point)
  • it includes a comprehensive set of material evidence of its different historical periods of occupation (domes, instruments, technical equipment), that is more than a century of scientific uses in the high mountains;
  • beyond this, it is a pioneering scientific and technical station at altitude with a number of other uses (weather observations, broadcasting...);
  • the Pic has had continuous scientific use, particularly for astronomy, and has always been a place alive with astronomy;
  • the importance of scientific work at the Pic du Midi, world class innovations (coronagraph), international cooperation;
  • major natural and cultural landmarks in regional history: its silhouette is unforgettable, as important a symbol of pyreneism as physical geography manuals, it is a symbol of the peaceful relationship between man and the high mountains;
  • a place of exceptional observation by day and night to which the pyrenean panoramas and the quality of the night sky are testament.


State of conservation and factors affecting the property

Present state of conservation 
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The buildings and observatories are regularly maintained. However, this maintenance is extremely complex and sensitive. See the section “Environmental Pressures” below for more information.


Factors affecting the property 
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Developmental pressures

The exceptional location of the Pic du Midi means that it escapes most of the pressures linked to urban or industrial development.

However, the presence of the nearby ski resort of La Mongie has, on occasion, resulted in the Pic being exposed to expansion projects to enlarge the skiable area. But the desire of the local elected officials to preserve the observatory’s integrity has always succeeded in keeping these attacks at bay.

Environmental pressures

The first is the high altitude and strong assaults it inflicts on buildings. Rain and melting snow seep into buildings. When temperatures drop, the water freezes and shatters the masonry. We must also mention the very strong winds that can blow a gale up to nearly 300 km/h, or thermal amplitudes reaching nearly 60°C. Without permanent maintenance work, the Pic would fall into ruin in fewer than 5 years (as was the case during the First World War).

<strong>Fig. 42</strong>. Winter at the Pic du Mid

Fig. 42. Winter at the Pic du Midi. The buildings are imprisoned under the frost and the snow (2008). Photo © Nathalie Strippe


The second reason is the complexity and variety of the building. 140 years of facilities and construction are superimposed on the summit. Modern concrete buildings are mixed with stone structures from the beginning of the century and they are all spread over nearly 8 floors and 1 hectare of ground. The maintenance of a building of this size and diversity at nearly 3,000 metres above sea level, demands important attention and resources. Which is not sufficient to ensure the homogenous integrity of the whole platform.

The last reason, also related to the altitude, is the seasonal maintenance. Throughout its history, the major work on the Pic du Midi could only be done during the summer (July, August, September) and modern means can do nothing to change this.

The Pic du Midi’s night sky is still today of very good quality. However, the increase in light pollution observed for more than twenty years in this region, has alarmed astronomers and elected officials of the Pic du Midi.

In order to diffuse this threat, the International Dark Sky Reserve project was launched in 2009. The Pic du Midi, accompanied by an extensive network of partners, is committed to completing this process, which goes beyond only the issue of access to the stars.


<strong>Fig. 43</strong>. Pic du Midi IDSR. The ID

Fig. 43. Pic du Midi IDSR. The IDSR, with its core and buffer zones, takes up 65% of the département Hautes-Pyrénées’ territory.
Photo © Agence Hotel Republique, Régie du Pic du Midi

Today, the 251 municipalities that make up the contours of the Reserve in the Hautes-Pyrénées, are mobilising to support the sustainable development approach. Establishment of a new mode of economical, sustainable and cleaner lighting, protection of the sky and the nocturnal environment, tourism development, are among the main actions that characterise this project. On 19 December 2013, the Pic du Midi IDSR was accredited by the International Dark Sky Association, making this Dark Sky Reserve, the first in France and the second largest in the world.

Today 40,000 public street-lights are involved in the programme to improve the lighting. The monitoring of the programme was used to measure an 85% decrease of the luminous flux emitted upward in converted villages. Since 2012, approximately 3,000 lights are improved each year.

<strong>Fig. 44</strong>. Lighting in the the vill

Fig. 44. Lighting in the the village of Aulon. Before and after the improvements made to the lighting under the Pic du Midi IDSR project (2013). Photos © Léa Salmon

Natural disasters and risk preparedness

Natural disasters in the Pyrenees affect the Pic du Midi indirectly. They disrupt the flow of tourists upon which the observatory’s work now depends. In June 2013, heavy floods affected the Hautes-Pyrénées, destroying many access roads, making them impassable for several months. The Pic du Midi in general, already very sensitive to bad weather, saw its attendance drop by more than 30% that year.

Visitor/tourism pressures

Tourism is now constitutive and essential to the work of the Observatory. The ’Pic 2000‘ project was the fruit of collective work between astronomers and local public authorities, helping to redesign the platform and its access in order to welcome the public without transforming or disrupting the scientific work. Most of the tourists visit during the summer. However the Pic stays open for visits all year and only closes for maintenance periods in November and April.

Number of inhabitants

The observatory has 10 permanent residents and an average of 5 researchers on the summit. However, the number of staff members that allow the Pic du Midi to operate is much greater. The Syndicat Mixte of the Pic du Midi and its technicians count over 50 employees. The Midi Pyrénées Observatory platform technique team is made up of 20 people. The Pic, as a university training centre, also welcomes many temps and PhD students.


Protection and management

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There are currently two concessions which manage the Pic du Midi Observatory and its infrastructure.

The buildings ensure the scientific work in the public domain of the French state. Its management is provided by the Paul Sabatier University in Toulouse via the Midi Pyrénées Observatory. The MPO is thus responsible for 4,000 m² distributed amongst the various observatories and technical areas related to science.

Since 1996, the Syndicat Mixte du Pic du Midi has been the new observatory concessionary. It is in charge of tourism infrastructures, technical elements (purification of the summit station, pumping station, generator), access to the site (and cable car stations) and human ressources (rooms, staff rooms, meeting room). Which also represents 4,000 m².

There is one final concession at the summit which is the exterior of the Pic du Midi Observatory. That is the Interdepartmental Building, property of the State and managed by the French Broadcasting organisation. These buildings together make up 2,000 m².


Protective designation 
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In 2003, the Pic du Midi became a “National Natural Site” under the title “Landscape Beauty”. This document, issued by the Ministry of Ecology and Sustainable Development, protects the integrity of the panorama terraces accessible from the observatory.

Since 2007 the observatory has been involved in a voluntary environmental quality programme in order to reduce its impact on the natural environment. It obtained the international certificate “quality, safety, environment” via the ISO 14001 standard.

The Pic du Midi is also the only tourist attraction of altitude to have achieved, on its own, the level of security required for an establishment to open its doors to the public. The observatory is certified ISO 9001 Version 2000 in security, infrastructure maintenance and public management.

In 2013, it received the International Dark Sky Association label for the preservation of its night skies (see the section entitled “Environmental Pressures” for more information).


Visitor facilities and infrastructure 
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    Date: 2015-02-12 10:08:41
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The observatory is equipped to accommodate an average of 100,000 visitors per year while preserving the architectural integrity of the site and its scientific work. For details, refer to the “Tangible Heritage”, “History and Development” and “Integrity and/or authenticity” sections.

Fig. 45. The terrace atop the Pic du Midi in the summer. Today tourists have access to 750 m² of terrace, the museographic space
under the Baillaud Dome and the restaurant in the Vaussenat Building (2013). Photo © Nicolas Bourgeois


Presentation and promotion policies 
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    Date: 2015-02-12 10:11:50
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The Pic du Midi is considered a hotspot and geosymbol of the Pyrenees, human adventure and science. For this, it is the subject of several development policies and protection.

In 2010, the Pic du Midi was chosen to be part of the “Grands Sites de la Région Midi-Pyrénées” (the Midi-Pyrénées’ Grand Sights). This label values natural and cultural sites as well as the most iconic architecture of the Region.



Photos and other AV materials 
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    Date: 2015-02-12 10:12:23
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A photographic inventory of the Pic du Midi property is in working progress with the Ramond Society and the Pic du Midi Observatory.


Most recent records or inventory 
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    Date: 2015-02-12 10:14:12
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See the section entitled “Movable heritage objects—small instruments, books, archives and photographs” for the Pic du Midi Observatory heritage inventories.


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Charlier B., Bourgeois N. (2013). ┬½Half the park is after dark. Les parcs et réserves de ciel étoilé: nouveaux concepts et outils de patrimonialisation de la nature.┬╗ L’Espace Géographique, 42, 200–212.

Cortella P. M. (ed.) (2009), ┬½Pic du Midi de Bigorre, portes ouvertes sur le futur.┬╗ Bulletin Pyrénéen, 239.

Davoust E. (2014), Pic du Midi, Cent Ans de Vie et de Science en Haute Montagne. Barcelone: MSM.

Dollfus A. (1961). The Solar System, Vol III, Planets and Satellites. Chicago: University of Chicago Press.

De Marco R. (1997). Le Pic du Midi, le Sommet Reconstruit. Mémoire de DEA, EHSS, Paris.

De Marco R. (2003). La Construction du Lieu à l’Époque de l’Utopie Véritable: Le Pic du Midi de Bigorre. Pour une Connaissance Sensible et Faisable du Lieu et du Paysage. Thèse de Doctorat, EHSS, Paris.

Martin H. (1989). ┬½Menaces sur le Pic.┬╗ Pyrénées Magazine, no. 1, 16–27.

Sanchez J. C. (2014). Le Pic de Bigorre et son Observatoire. Paris: Cairn Editions.

Terrancle P. (1995). ┬½Pic du Midi, voyage à l’intérieur d’un mythe.┬╗ Pyrénées Magazine, no. 37, 20–35.

Terrancle P. (1997). ┬½Pic du Midi, le grand projet.┬╗. Pyrénées Magazine, no. 54, 58–73.


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