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RMxAA (Serie de Conferencias), 51, 1–8 (2019)

ASTRONOMICAL OBSERVATORIES: FROM THE PREHISTORY TO THE

XVIII CENTURY

M. A. Castro Tirado1,2

ABSTRACT

We describe the development of astronomical observatories since the prehistory until the late XVIII century, andhow an evolution of several millennia took us from very elementary structures to buildings hosting telescopesand domes in which science was the fundamental, but not the only motivation.

RESUMEN

Describimos el desarrollo de observatorios astronomicos desde la prehistoria hasta finales del siglo XVIII, ycomo la evolucion de varios milenios ha pasado de estructuras elementales a edificios albergando telescopios ycupulas en los cuales la ciencia era fundamental, pero no la unica motivacion.

Key Words: history and philosophy of astronomy — telescopes

1. INTRODUCTION

Astronomy originates from the primitive rela-tionship between man and nature. Especially withits most unreachable component: the sky.

In antiquity, some of the stars were consideredgods and the sky was their residence. Thereforethere was a strong connection between astronomyand religion that only began to diverge a few cen-turies ago. In addition to this spiritual sense, thebeginnings of this science point to the instrumental-ization of the firmament as a system of measurementof time periods and as a means of orientation.

Beyond the numerous artistic representations ofthe Sun, Moon and stars that have been found,or of the written testimonies that have lasted intime, there is evidence of this astronomical prefer-ence through the incidence of some celestial phenom-ena in the arrangement of certain constructions orarchaeological sites.

In any case, although certain vestiges of ancientcivilizations evidenced an outstanding impact of as-tronomy in its culture through its architecture orurbanism, it will be the proto-observatories, under-stood as places conceived exprofeso to be the onesdestined, in some way, to the study of the heavens.Those that stand out as points of interest to knowthe way in which these people approached the studyof this science.

These spaces will be where contemporary as-tronomical observatories have their deepest roots.

1Instituto de Astrofısica de Andalucıa (IAA-CSIC),Granada, Spain.

2Departamento de Ingenierıa de Sistemas y Automatica(Unidad Asociada al CSIC), Escuela de Ingenierıa Industrial,Universidad de Malaga, Malaga, Spain.

Dreyer (1953), Hall (1983), Magli (2009), Sayili(1960) and Thurston (1994) have been consulted forthe present review.

2. STONE AGE

The earliest set of recordings in Prehistory todate is the Goseck Circle (Figure 1). It consists of aneolithic structure located in Germany dating about7000 years old. It is a solar observatory of annu-lar plant, with an inner radius of 48 meters and anouter radius of 82. It is composed of four concen-tric rings, being from outside to inside, the first amound, the second a moat and finally two palisades.These crowns have three discontinuities aligned ra-dially and focused respectively towards the north,southeast and southwest. These openings are ori-ented towards the sunrise and sunset on the wintersolstice.

Of a similar chronological period is the megalithicset of Nabta Playa, in Egypt, to the south of Cairo.It presents a circular composition of almost thirtyperimeter stones marking doors with larger pairs andcontaining some inner clusters.

Although this place could accommodate some re-ligious uses associated with the nomadic cultures ofthat context, an archaeoastronomical character isrecognised. Through the study of the firmament thecircle would acquire functions of calendar, markingtwo of its doors an alignment with the summer sol-stice, and point of orientation in the desert.

3. PROTOHISTORY

Sometime later, around 3000 BC Carahunge (alsoknown as Zorats Karer) can be situated. Located in

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Fig. 1. Reconstruction of Goseck Circle.

Armenia is this composition of more than one hun-dred stones arranged as menhirs of between one andthree meters height with plant in form of oval ring.

The main singularity of this formation is thatpart of the rocks that compose it have a perforationof between 5 and 20 cm diameter that crosses themand that, according to what has been seen, pointtowards significant events as the Sun at dawn anddusk in the winter solstice.

Between 3600 and 2500 BC the megalithic tem-ple of Mnajdra is erected, located on the south coastof Malta. The vestiges that have survived until thepresent day consist of three constructions of lime-stone, that although they are not connected theyare grouped around a place between the remains ofa major complex but scarcely conserved.

Beyond the discovery of signs that point to a re-ligious character of the constructions, there are ar-guments that support the idea that identifies thesouthernmost temple as an observatory dedicatedto the study of heaven and time. In particular itsorientation and configuration cause the sunrise ofthe summer and winter solstices passing through themain door and illuminate the megaliths located re-spectively left and right of the door. Also, at thespring and autumn equinoxes, at dawn, the Sun en-ters through the same door crossing the main naveorthogonally to the altar.

The famous Stonehenge (Figure 2) is located inEngland, west of London, and its construction ex-tends from 3100 to 1600 BC. Although an importantmegalithic structure remains, a considerable part ofthe initial composition has been lost. However, theremains are sufficient so that the studies have beenable to define its original configuration.

It displays a circular plant of about 30 metersof diameter conformed by concentric constructions.

Fig. 2. Stonehenge.

The outer perimeter was delimited by a series of ver-tical blocks that supported lintels forming a closedring. Concentrically there was a circumference ofsmaller monoliths that surrounded five pairs of largestone blocks forming doors. The interior was occu-pied by a set of menhirs.

The alignments that occur in Stonehenge throughits gates during the sunrise and sunset during thesummer and winter solstices are obviously inten-tional. This shows a certain degree of astronomi-cal knowledge on the part of its constructors anddenotes its function as observatory and calendar be-yond other ritual or religious uses associated to thesefacts.

In any case, the astronomical functions of thesestructures were quite limited. It is even possible thatthe scientifically valuable activity can be limited tothe determination of the positions and orientation ofthe elements of the set. A study of the sky is re-quired with systematic and intentional observationscompared to these reference points that allow to es-tablish a pattern from which to erect these construc-tions. Once the device is ’calibrated’, using it is notmuch more scientific than looking at the hands of awatch.

4. ANCIENT HISTORY

The above mentioned cases allude to primitivecivilizations, with a low degree of technification andeven, frequently, with nomadic habits. This makessimple the identification of their constructions.

However, the evolution towards more complexcultures makes this difficult. This is so because themore advanced civilizations tend to create settle-ments with multiple buildings in which it is unnec-essary to reach the degree of specialization neededfor the function of observation as such. Since no

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Fig. 3. The Pnyx at Athens.

scientific instruments had been developed that re-quired demanding conditions, this recognition of thesky could be carried out with the naked eye in almostany construction or even in the vicinity of these openskies.

In the case of Mesopotamian astronomy, al-though there is certainty of its development, thereis little knowledge about the instruments used forthe study of the sky, leaving only a few items in mu-seums. So it is very difficult to clarify where the ob-servatories of this civilization were located, althoughit is possible that these were incorporated as suitablespaces for that objective in other buildings. Or eventhat certain rooms or areas, such as the terraces ofthe ziggurats, were used in a timely manner for thispurpose.

Precisely, according to some writers of the antiq-uity such as Herodoto, Plinio or Diodoro, the Towerof Babel was used for the astronomical observationof stars.

Something similar happens with regard to Greekculture in the Classical antiquity period, with an im-portant tradition in astronomy and with a crucialrole in the history of this science. There is no evi-dence of built observatories as such.

Nevertheless, there are vestiges of some placesused for the study of the sky, like the Pnyx in Athens,which dates from sixth century BC (Figure 3). Itsastronomical use has been recorded since at least thefifth century BC. Even if this place was not only des-tined to this function, it was destined to the politicalassembly, as its suitable characteristics propitiatedthe new use. Formed by a semicircular flat platformin an elevated position and with a wide view of thesky, it ended up receiving instruments of astronomi-cal study (the heliotrope of Meton).

Fig. 4. The Sun through the Pantheon.

Regarding the Roman influence, although its rel-evance is smaller than the one inherited from othercivilizations, it is possible to stand out points of ce-lestial investigation the Field of Mars of Rome, wherethe solar clock of Augustus was located, and thePantheon, constructed during the second century, inwhich, thanks to its oculus, solar studies were car-ried out. Its design and orientation make it possiblefor a beam of light during the zenith of the equinoxto cross the building from the oculus to the portico,through a lattice-work over the main door, indicat-ing that event (Figure 4).

5. POST-CLASSICAL HISTORY

At the other end of the world is Cheomseong-dae, in South Korea. It is the oldest astronomicalconstruction of the Asian continent. It consists of abottle like shape tower, about ten meters high andabout six meters diameter, composed of granite ma-sonry (Figure 5). It is kept in a great state of preser-vation.

The main function of this construction is to raisethe astronomical instruments and their user over thefloor. The user accesses by means of a ladder to anentrance located at the middle of its height, throughwhich it passes into the interior space: a cylinder hol-low with a second ladder to reach the upper opening.

The main historical contribution of China to as-tronomical constructions is the Great Dengfeng Ob-servatory, built around 1279. It is a tower ∼10 me-ters high, with leaning walls of stone and brick,whose peak was known as the “platform of obser-vation of stars”. It has two rooms at the top for thestudy of the sky from a sheltered space and a largegnomon that is part of the structure itself.

Even without receiving any influence from foreigncivilizations, the different cultures of the Americancontinent also present constructions related to the

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Fig. 5. Cheomseongdae.

study of the sky. Among these cultures the Mayastands out, especially, for its advanced astronomyand for the complexity of its observatories.

Of these astronomical structures can be high-lighted the Caracol in Chichen Itza: a circular plantconstruction of 12.5 meters high with an internal spi-ral staircase to access the top that gives name tothe observatory. Built between the 8th and 9th cen-turies, it was used to set astronomical observationpoints and to follow the movements of the planetVenus.

Coinciding with the beginning of the MiddleAges, begins a time of cultural darkness in the West-ern world that would not escape astronomy. Dur-ing this period, Islamic culture will play an essentialrole in the history of this science, preserving the vastGreek knowledge of this subject, and incorporatingits own inquiries, which would be recovered by thewest during the thirteenth century, especially by theSchool of Translators of Toledo.

For the Islamic people astronomy has an impor-tant value, since the Koran provides numerous refer-ences to the Sun, the Moon or the stars, influencingtheir daily life through religious customs such as thehours of prayer or the beginning of Ramadan.

The astronomical tradition is reflected in the me-thodical study of the firmament in temporary obser-vation posts.

The construction of the observatory in Maragha,northwest of Iran, is part of the period that rep-resents the highest point of the evolution of theIslamic observatory, during the thirteenth century,when they move from these temporary posts to ascientific institution located in a building.

The main building was a twenty-two meters di-ameter circular tower. The central space was alignedfrom north to south with the meridian, containing amural quadrant that occupies the entire central vol-

Fig. 6. Remnants of the observatory of Samarkand.

ume. To the sides of this space appeared perpen-dicularly rooms of smaller size to house the libraryand instruments of observation and working tables.Above this tower there was a small dome with anoculus to measure the movements of the sun.

The advances made in Maragha had their influ-ence in later astronomical constructions. Thus theobservatory is conceived as a collaborative institu-tion in which several researchers developed a partic-ular study during a certain period of time and withhomogeneous working conditions.

This was reflected in the observatories of Istanbulor Samarkand (Figure 6), with a design similar tothat of Maragha.

6. MODERN HISTORY

The first references to an European observa-tory point towards Nurnberg, where astronomer andmathematician Johannes Muller von Konigsberg car-ried out his observations at the end of the fifteenthcentury. Shortly after, the observations developed byCopernicus in Frauenburg, Ermland and Allesteinduring the first half of the sixteenth century arerecorded.

However, it appears that these observations oc-curred at various locations in the open field.

In any case, there is no evidence to suggest thatany of these astronomers had an observatory. Fur-thermore, they lacked an observatory as such. Theirwork paved the way for the subsequent projects ofWilhelm IV and Tycho Brahe.

6.1. The first modern observatory

In the Landgraviate of Hesse-Kassel, in 1560,Landgrave Wilhelm IV, fascinated by this science,orders to construct a balcony-like platform at his ur-ban palace. This viewpoint aimed at studying the

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Fig. 7. Representation of Uraniborg by Tycho Brahe.

sky by means of astronomical instruments. Althoughinitially the landgrave itself would make the observa-tions, soon other astronomers would be incorporatedfor the development of a permanent investigation.

Even if this platform I just mentioned may beconsidered by some authors as the first observatoryof the Modern Age, it does not represent any sub-stantial qualitative advance compared to those ofprevious periods, resulting, to a large extent, fromimprovisation.

However, the relevance of the Hesse-Kassel obser-vatory is no smaller, since it would serve as a catalystfor the evolution of this building typology. In 1575Tycho Brahe visited the Landgrave Wilhelm’s facil-ities and, a few months later, inspired by that trip,began to build in Denmark which, now, will be thefirst modern observatory.

Tycho counted on several architects for the de-sign of Uraniborg, in which its enormous relevancedoes not lie on its stylistic features but on its form-functional conception.

So far, the instruments of observation were sim-ply placed on platforms chosen with certain criterion.

Astronomer Giovanni Domenico Cassini wouldpoint Uraniborg as the birthplace of modern astron-omy.

At Uraniborg stands a building that respondsand conforms to a specific program of uses. Thearea for astronomy rises to the platforms at the top,allowing the instruments to view the sky and freeingthem from obstacles. The alchemy is carried out onthe basement, closest to the ground to take advan-tage of the heat of the fires that heat the buildingfrom below up. In the middle part, there is a study

Fig. 8. Representation of Stjerneborg by Tycho Brahe.

area, service spaces and residential uses (Figure 7).

The project takes into account the segregationof uses according to their compatibility and their ar-rangement according to their needs. It also considersissues as important as lighting, heating and ventila-tion.

Nevertheless, the project has some flaws in itsconcept, with instability of observation platforms be-ing particularly important.

This research center will have such an impactthat it will become a reference to be imitated by laterEuropean observatories, if not in its appearance, atleast in its conception; and will mark the future ofthe later observatories in which the relationship be-tween science and architecture will be essential.

Only a few years after completing Uraniborg, Ty-cho opened a new observatory in the vicinity of thefirst one with the intention of solving stability prob-lems: Stjerneborg (Figure 8).

For this, a partially buried construction is usedin which the observation instruments are installed onfirm pier.

Stjerneborg groups a series of specialized roomsfor each particular instrument, with all of themaround a central workspace.

These spaces represent their singularity in a spe-cific type of cover (domes, demountable slabs ...) andin the definition of their floors, which adapt to theworking conditions for each instrument.

It will not be until the late 17th century whenother astronomical observatories that have the insti-tutional entity presented by those of Tycho Brahebegin to appear.

Meanwhile, the evolution of this science in abranched way entailed different techniques of study

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that, sometimes, moved away from a direct observa-tion. This is the case with the camera obscura.

Despite lacking the right architecture for observa-tion, Renaissance astronomers maintained their re-search performance in line with their significant op-erational limitations. That is, by accommodatingexisting constructions and spaces to an astronomicalfunction.

Tycho Brahe, dedicates a section of his work As-tronomiae Instauratae Mechanica to an architecturalreading of these buildings, in which he emphasizesthe importance of the place of implantation or thefact that the design responds to the practical func-tion.

Some years later, Juan Caramuel, a cistersianmonk, will dedicate an article from his treatise Ar-quitectura Civil Recta y Oblicua to the same ques-tion. However, his perspective, while maintaining afunctional vision, is much more aseptic and idealizedthan that of Tycho, given that Caramuel, not beingan astronomer, is not involved and does not devoteso much attention to the user of the building.

6.2. The design taking into account the use of thetelescope

The incorporation of the telescope as main toolof work would mark the future of the design of as-tronomical observatories.

However, since the first telescopes used to be ofsmall size and quite manageable, many astronomersconcluded that they could make their observationsfrom the windows, balconies, terraces or gardens oftheir own residence. That is why, during this period,the development of the observatories goes towardssimple structures or, directly, to additions on pre-existing buildings where platforms are installed fromwhich the sky is better visualized.

For example, in Holland in 1633 the Observatoryof the University of Leiden was founded, building anextension on the existing roof and being the oldestin Europe integrated into a public institution.

Throughout the seventeenth century, variousstructures were established with an observatory vo-cation throughout Central Europe, highlighting theRundetarn in København: a case in which, despitethe greater architectural complexity, the astronomi-cal bases remain very elementary (Figure 9).

It is a tower that has a helical upward slopingdevelopment around a hollow cylindrical core. Atthe top, more than forty meters high, the ramp opensonto a slightly inclined platform with views of threehundred and sixty degrees around the nucleus.

In spite of the apparently ideal conditions of theplatform, it lacked the necessary characteristics for

Fig. 9. Rundetarn in Copenhagen.

a good observatory, as its director Ole Rømer wouldrecognize.

The growth of the telescopes for the sake ofgreater magnification gave rise to stability problemsfor pointing objects in the sky, which was solved inthe instruments of zenith in which the telescopeswere installed vertically attached to some type ofstructure which ensured its fixity and balance.

This is the case of Robert Hooke’s telescope atGresham College to measure parallax. Faced withthe need for an installation in a high and narrow,undisturbed space, for an extended period of time,he chose to accommodate it in his own residence.This was mounted vertically, through the deck anda floor, to make the observations from the lower level.In addition it incorporated a system that allowed itscover and shelter in bad weather or when it was notin use.

On the other hand, towards the second half ofthe century, began a race to construct telescopes ofgreater length, reason why aerial models were de-veloped increasingly longer and more complicated touse. These instruments became so long that theycould no longer fit inside buildings. In addition tothe problem of obtaining a location in which to in-stall them, their exposure made difficult their han-

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Fig. 10. Johannes Hevel’s rooftop platform.

dling and the tasks of measurement or data collectionnecessary for the investigation.

Take for example Robert Hooke’s twelve-meter-long telescope at Gresham College in London orChristian Huygens’ devoid of casing models.

Another case is the Johannes Hevel, who installeda platform on the roof of his home from which tomake observations with his telescopes. He devel-oped increasingly long instruments until he got oneso large that he was forced to take it out in the opensky to the outskirts of the city, installing it on a polesuspended by several braces (Figure 10).

Observation with a telescope of these dimensionsshould not have been simple, on the contrary. Asmall group of collaborators was necessary to trans-fer, erect and assemble perfectly the sections of thefield telescope, as well as for its handling during theobservations.

To the complex operation of the telescope, dueto its size, we must add the difficulties of workingexposed to the elements.

Taking another step, Hevel presents in his Machi-nae Coelestis of 1679 a theoretical project for an ob-servatory. The design is based on the superpositionof two well-differentiated elements: a great platformto be able to make observations with several tele-scopes simultaneously and a rotating tower to sus-pend them.

Rømer, director of the Rundetarn, moves the ob-servations to the architectural framework of his ownhouse, where he occupies a south-facing room forsuch use, where he installs his “machina domestica”.

A particular observatory based on a meridiantransit telescope adapted to the architectural cir-cumstances existing in his dwelling, where the con-ditions of stability and climatization are favorable.

To what extent did the architecture condition itsobservations? That is to say, did Røemer design adevice that, by pure chance, could adapt to the spacethat already had or devised his “domestic machine”to adapt to the architecture of his house? The secondpossibility seems more likely, less random.

Fig. 11. The Flamsteed House at the Greenwich Obser-vatory.

The Paris Observatory was born as a response tothe demands of the newly established Academie desSciences, in a context of full boil Illustration, whoseaim was to symbolize greatness and renown throughknowledge.

The design was commissioned by a famous archi-tect and member of the Academy: Claude Perrault.The project developed by him had a monumentalcharacter and looked more like a palace than a build-ing designed for astronomy. Despite Perrault’s goodintentions, the initial proposal had many drawbacks,a result of the lack of knowledge and lack of astro-nomical experience.

Luckily, during the construction, GiovanniDomenico Cassini joined the project as an astron-omy consultant, to contribute with his knowledge.

From this team resulted the design changes thatended up giving rise to a building that hosted bothscientific activity and other service functions. In ad-dition, it was full of successes and innovations thatwould be transferred to observatories and even otherconstructive typologies, being especially importantthe use of the flat roof.

6.3. The introduction of the dome

The Greenwich Observatory. In this case, thedevelopment of maritime trade routes and militarydominance of the seas causes the observatory’s mainobjective to be functional and practical: to developnavigation.

Sir Christopher Wren, professor of astronomyand architect, would be named for this task. Andhe also collaborated with the astronomers Flamsteedand Hooke.

Thanks to this team, a building was erectedwhere the science and the quartermaster or servicesof support of this one coexisted (Figure 11).

Although the project presented all the necessaryconditions to develop the astronomical activity inan appropriate way according to the methods of itstime, the economic restrictions involved the use of an

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Fig. 12. The Spanish Royal Navy Observatory in SanFernando.

existing structure, which prevented its proper orien-tation.

This fact and the very development of science,were phasing out the observatory, which was adaptedby modifications and extensions over time.

The Observatory of San Fernando (Cadiz) inSpain has a purpose homologous to that of its Britishpredecessor: to improve navigation. In this case,in addition, the institution is linked to the MarineGuard Academy, with a dual function: research andtraining (Figure 12).

Initially the Observatory is installed in an exist-ing construction: the Castle of the Villa. It occupiesa battered tower where, despite occupying a privi-leged position, its operation is complicated and inef-ficient.

Years later it would end up moving to a build-ing specifically for the Observatory, designed by theMarquis of Urena, which would include spaces for as-tronomy and calculations derived from observation,and other zones of services for occupants and scien-tific activity.

The Madrid Observatory arises from the conta-gion of Illustration thought that spreads throughoutEurope as an institution of knowledge and prestige.For this reason, its location is taken into account,in the extension of a cultural axis with the PradoMuseum and the Botanical Garden.

The project is entrusted to the architect Juande Villanueva who, beyond satisfying the functionalrequirements (both astronomical and service) takesinto consideration the position that the building willoccupy, high and visible from the entire urban front(Figure 13).

As a result of this, the observatory is developedas a monumental composition in which the wholeenvironment will be part of the project, including abody of entrance and the landscape treatment of thesurroundings.

Fig. 13. Madrid Royal Observatory.

7. CONCLUSIONS

We have described the development of astro-nomical observatories since the prehistory until thelate XVIII century. At this stage, I would like topoint out how an evolution of several millennia tookus from very elementary structures to buildings inwhich science was the fundamental, but not the onlymotivation.

These are the key points which have beenreached:

• The best possible conditions for the develop-ment of astronomy.

• A compromise between astronomical activityand the needs of its users.

• A balance between functionality and comfort.

• The inclusion of movement and adaptation toclimatic and lighting conditions.

• An accommodation to existing technology.

• The consideration of the environment, positionand landscape.

Acknowledgements: We are grateful to Juntade Andalucia grant under project TIC-2839.

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