Observatory

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Classic observatory dome: Large refractor of the Vienna University Observatory from 1885, 11 m focal length
Open, azimuthal design: Large binocular telescope with two 8 m mirrors
Modern 2-meter reflector telescope: The Fraunhofer telescope on Wendelstein

An observatory or an astronomical observatory (from Latin observare = to observe) is a place with scientific instruments for observing the starry sky . In addition to individual celestial bodies of the solar system and the Milky Way (stars, star clusters, nebulae), extragalactic celestial objects are the target of observation.

Scientific observatories are usually built on elevated locations and protected from the weather by a dome . When choosing the location, the greatest possible number of clear nights, little interfering light and little air turbulence are essential. The latter is given where (especially in the mountains) laminar air currents prevail.

In the case of observatories for educational purposes ( people's observatory ) or amateur astronomy ( private observatory ) , these requirements are less important than easy accessibility.

For observations in visible light, near infrared and UV, mirror telescopes and astrographs are predominant today, while lens telescopes (refractors) and transit instruments (for positional astronomy) are declining. In addition, there are numerous radio telescopes , which are hardly included in the term “observatory”.

Features of observatories

A whole "observatory campus" on La Palma, Roque-de-los-Muchachos-Observatory

The appearance of today's observatories is usually characterized by one or more domes , the

  • on the one hand can be opened for observation and rotated in the desired direction ,
  • on the other hand, should protect the instrument placed underneath when closed,
  • The light-painted dome ensures that the air is consistently cool thanks to its good reflection and insulation against solar radiation (see nocturnal cooling ). However, the remaining thermal effects cause the so-called hall refraction .

The instruments themselves (especially the telescopes) are mounted on their own pedestals that are mechanically strictly separated from the rest of the building to protect them from shocks and vibrations . For these pillars , which are deeply rooted in the natural rock , the classic, ventilated brick construction is still a mechanically and thermally good solution, while concrete is less favorable (possible temperature and internal stresses , noticeable pillar rotation ). In the case of heavy telescopes, their foundation must reach down to at least two meters in solid ground (if possible in the natural rock), with loose rock even up to 10 meters.

The modern large telescopes , which have mirrors up to 10 m in diameter and in the future even 40 m, are no longer housed in domes, but mostly in cube-shaped protective structures that are opened for use. For weight reasons, the mechanically simpler azimuthal mount is used here instead of the classic equatorial mount .

Research, public and private observatories

The term observatory includes research stations in various natural sciences such as meteorology or biology, but is also used for artificial earth satellites that carry astronomical telescopes. These satellites usually carry several instruments that can observe the same target or can be controlled separately (see satellite technology ).

Structures with a special construction that are used to observe astronomical phenomena such as the summer or winter solstice are sometimes also referred to as observatories . As solar observatories , they can often be assigned to a prehistoric culture where the course of the sun was observed (e.g. Goseck or Stonehenge circular ditches ). Modern examples are the star garden operated by the Austrian Astro Association in the south of Vienna and a similar one in the Ruhr area .

The term observatory, on the other hand, means fixed, predominantly astronomical observatories. One distinguishes

  • Research observatories , which are mostly far from cities, have large instruments and a considerable number of employees. They usually belong to a university or academy and pursue national research projects or those in international cooperation. They are the main subject of the following sections.
  • Public observatories , which are mainly used for public tours and adult education . Most of the time they are sponsored by astro clubs or the local community. Similar objectives pursue school Observatories . Sometimes both types are combined or are equipped with planetariums . In the latter, however, no celestial bodies are observed, but the astronomical objects are artificially projected.
  • Private observatories , on the other hand, are operated by individual, mostly well-off amateur astronomers , and occasionally by associations. Some also offer star tours to the public or the neighborhood on so-called astronomy days . Many observation areas are set up on residential buildings and protected with small domes or a sliding or rolling roof . On green spaces they are called garden observatories. Less complex, but more flexible, they are designed as terrace or roof observatories , especially with portable telescopes.

Choosing the location of research observatories

The question of suitable locations became more and more important in the 19th century due to the expansion of cities. Because the light dome of large cities can often extend 50 to 100 km. The observatories, which used to be built near royal courts, were gradually relocated to sparsely populated areas or to the mountains .

In addition to the aspect of low interfering light, it is also important to choose a suitable location

  • an area with a favorable climate (frequent high pressure situations, long hours of sunshine , low tendency towards storms)
  • a terrain shape with even air flow, which promotes seeing (low air turbulence). So divorce z. B. many mountains with a good climate, but asymmetrical summit shapes
  • rocky subsoil for a stable foundation of the instrument pillars .
  • Favorable transport connections and other infrastructure are also important.

Instruments

The observations or measurements are mostly carried out with telescopes (lens telescopes or mirror telescopes ) or astrographs , now increasingly also with antenna technology (radio astronomy) or with automated transit instruments for position astronomy. Most observatories observe in visible light, with the earlier visual methods being largely replaced by photographic and optoelectronic ones.

Until about 1620 the observatories were almost exclusively set up for free-eyed observation of the sky, equipped with meridian circles or sextants, armillary spheres , gnomon or large sundials (see also Astronomical Phenomenology ). For thousands of years, astrometry (determination of star locations and movements, celestial mechanics and time determination) has dominated scientific activity , which was only supplemented (and temporarily pushed into the background) from 1850 by astrophotography and astrophysics . Today, the work of high-altitude observatories with clean and dry air (European high mountains, Hawaii, Chilean Andes) increasingly focuses on non-visual radiation areas such as near infrared , UV and radio radiation , while the shorter wavelengths (UV and X-rays ) are largely reserved for space telescopes stay. Observatories on the moon are also being planned.

history

Prehistory, antiquity and the Middle Ages

Megalithic observatory in Nabta-Playa
Stjerneborg

Currently the oldest dated Observatory of the history system in force is possibly the county grave system of Goseck from the 5th millennium v. Chr. The megalithic circle in Nabta Playa in the Nubian Desert could also fall into this time. Other systems date from around 3000 BC. BC ( Stonehenge ) or 1200 BC BC ( Boitin stone dance ).

The Cheomseongdae Observatory in Korea is the oldest in the Far East . China has a long tradition of building observatories. In the Tang Dynasty , 20 solar observatories were built for the creation of the Da Yan calendar 729  AD , with 10 observatories being distributed along the 114th degree east from Central Asia to Huế to check the spherical shape of the earth. The Yuan dynasty had 27 large observatories built for the Shou Shi calendar in 1281, with the Gaocheng observatory near Dengfeng in Henan Province still in good condition.

In Peru is the 2300 year old Chanquillo Observatory, which consists of 13 towers on a mountain ridge. Whether the megalithic complex in the Armenian Zorakarer is an astronomical facility is highly controversial.

The first forerunners of the "classic" observatories emerged in the late Middle Ages and the time after. They were home to instruments for measuring star words, for example quadrants or astrolabes , or large sundials . Examples are the Rasad-e Khan observatory by Nasir Al-din al-Tusi , the observatory of Ulug Beg , Uraniborg and Stjerneborg , the observatory of Tycho Brahes or the Jantar Mantars of Maharajas Jai Singh II.

Modern times

Royal Greenwich Observatory

After the invention of the telescope in 1608, the first observatories in the current sense emerged in the following decades. From 1700 some belonged to physical cabinets , as they were maintained and promoted by nobles and other patrons during and after the Enlightenment . Often it was a question of extended attic storeys, attached towers or the like. Independent observatory buildings were often designed as astronomical towers , such as the Kremsmünster observatory (Upper Austria), the Prague Clementinum or the Mannheim observatory .

At the beginning of the telescope era, the Paris Observatory 1667 and the Royal Greenwich Observatory 1675 were built. The first observatory after Stjerneborg where the instruments were placed in a single-storey building was the Seeberg Observatory in Gotha, which opened in 1790 was taken. These early observatories were mainly devoted to astrometry (determination of star locations and planetary orbits) and also served as base points for navigation and land surveying .

Observatories only became accessible to the public after the construction of public observatories in the 19th century. The first school observatory in Germany was founded in Bautzen , East Saxony , in 1872 .

Many important observatories in Central and Northern Europe were founded between 1790 and 1830, including those in Hamburg-Altona, Munich, Düsseldorf, Gotha, Leipzig, Halle, Königsberg and Dorpat. Russia and the USA followed suit in 1839 with St. Petersburg-Pulkowa and Harvard. This wave of founding is mainly related to the successes of celestial mechanics (planetary orbits, comets, asteroids, double star research, star catalogs), as well as the development of measurement technology. In contrast, the university observatories in the southern half of Europe were mostly built earlier. The second founding boom can be seen at the turn of the century and brought about the development of astrophysics  - see, among others, Potsdam (astrophys. Inst.), Vienna (Univ. And Kuffnersternwarte), Zurich and the large observatories in the USA such as Yerkes, Lick and Lowell. These included some private observatories that are important for research .

The Vienna University Observatory opened in 1883 . Today the observatory park is located in a densely populated area (Vienna XVIII)

A sky that is as dark as possible (low light pollution ) is important for the quality of the observation . Nevertheless, until the end of the 19th century, most observatories were located near or even in cities - also to be close to the financier, generally the local royal court. For the current location, see the previous sections.

The growth of cities and the associated light pollution (light smog) , which increasingly impaired observations, led in the 20th century to a shift to increasingly remote areas that were not yet affected by light smog, such as mountains , initially closer mountains such as the Pyrenees or the Alps and finally in areas far away from larger settlements and with clear and calm air, such as on Mauna Kea in Hawaii or in the Atacama Desert in Chile .

At the same time, technological progress made it possible to manufacture ever larger telescopes that can capture ever weaker amounts of light and thus allow observations into ever greater depths of space. These instruments also reach their limits due to the natural unrest in the air . Powerful adaptive optics are able to almost completely correct this disadvantage, but usually only in very small image fields. One way out was in the construction of space telescopes that enable observations outside of the disturbing influence of the earth's atmosphere , such as the Hubble space telescope . In addition, space telescopes have been developed to enable observations in spectral ranges that are inaccessible from the ground, such as in the far infrared or in the range of X-rays .

Individual observatories and observatories

Prehistoric and early historical buildings (selection)

State Observatory Heidelberg -Königstuhl
Historical photo of the Sonneberg observatory

Observatories in Germany (selection)

Research institutes

Public observatories

Volkssternwarte Aachen
Regiomontanus Observatory Nuremberg, public observatory from 1930
Fritz Weithas Observatory in Neumarkt, Upper Palatinate
Zollern-Alb observatory in Rosenfeld, Swabian Alb
Zweibrücken public observatory

Other observatories

Stuttgart observatory
Peterberg Observatory
Leopold Figl Observatory on the Schöpfl (900 m), main dome of the 150 cm reflector telescope

Observatories in Austria (selection)

Kanzelhöhe solar observatory on the Gerlitzen

Observatories in Switzerland (selection)

Urania observatory Zurich

Research institutes

Private and public observatories

Historical observatories (selection)

Observatory of Kremsmünster Abbey (1749) with natural science. Collections
Lilienthal observatory; Third asteroid Juno discovered here in 1804

Other observatories (selection)

In the airspace (selection)

In space (selection)

Measures regarding the corona pandemic

At the beginning of the lockdown in March 2020 due to the corona virus, almost all observatories stopped their public tours. Restricted operation was only possible where there was sufficient space outdoors or very well ventilated domes.

Since the relaxation, which began in different countries in June or July, various measures have been tried out in public observatories and astro clubs [1] , [2] in particular

Public observatories with a larger outdoor area or astro clubs can be

See also

literature

  • David Leverington: Observatories and Telescopes of Modern Times - Ground-Based Optical and Radio Astronomy Facilities since 1945. Cambridge University Press, Cambridge 2016, ISBN 978-0-521-89993-2 .

Web links

Commons : Observatories  - collection of images, videos and audio files
Wiktionary: Observatory  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. ↑ H. Zimmermann, A. Weigert: ABC Lexicon Astronomy . Spectrum Academic Publishing House, Heidelberg 1995.
  2. ^ GD Roth: Kosmos Astronomie-Geschichte: Astronomers, Instruments, Discoveries . Kosmos-Verlag, Stuttgart 1987.
  3. ↑ Most modern observatory in Central Europe opened orf.at, August 12, 2018, accessed on August 12, 2018.