Potsdam Great Refractor (Große Refraktor) is an historic astronomical telescope in an observatory in
Potsdam, Germany
Potsdam () is the capital and, with around 183,000 inhabitants, largest city of the German state of Brandenburg. It is part of the Berlin/Brandenburg Metropolitan Region. Potsdam sits on the River Havel, a tributary of the Elbe, downstream of B ...
.
Completed in 1899, it is a double telescope for astronomy, a
great refractor
Great refractor refers to a large telescope with a lens, usually the largest refractor at an observatory with an equatorial mount. The preeminence and success of this style in observational astronomy defines an era in modern telescopy in the 19 ...
with two objectives of different size on the same
equatorial mount
An equatorial mount is a mount for instruments that compensates for Earth's rotation by having one rotational axis, the polar axis, parallel to the Earth's axis of rotation. This type of mount is used for astronomical telescopes and cameras. The ...
.
One lens in 80 cm in aperture and the other is 50 cm.
The 80 cm diameter lens was designed for
astrophotography
Astrophotography, also known as astronomical imaging, is the photography or imaging of astronomical objects, celestial events, or areas of the night sky. The first photograph of an astronomical object (the Moon) was taken in 1840, but it was no ...
, and the 50 cm diameter lens for visual work.
The telescope was made by Repsold,.
The objective lens glass blanks were made in
Jena
Jena () is a German city and the second largest city in Thuringia. Together with the nearby cities of Erfurt and Weimar, it forms the central metropolitan area of Thuringia with approximately 500,000 inhabitants, while the city itself has a popu ...
by Schott, and the lenses figured by Steinheil of Munich.
History
![Potsdam Great Refractor](https://upload.wikimedia.org/wikipedia/commons/4/43/Potsdam_Great_Refractor.jpg)
An observatory had been established in the late 1870s near Potsdam, and had gained notice for its work on photographic
spectroscopy
Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. Matter wa ...
of stars.
A new telescope was acquired by 1899, to continue this work and by 1904 the interstellar medium was discovered spectroscopically. The telescope mostly survived to the 21st century with an archive of
photographic plates
Photographic plates preceded photographic film as a capture medium in photography, and were still used in some communities up until the late 20th century. The light-sensitive emulsion of silver salts was coated on a glass plate, typically thinn ...
, and is a popular tourist destination in the modern day after the site was restored.
With this type of telescope, the dome opening must move in synchrony with the telescope or the view would be blocked; in addition the floor inside the dome also moves to keep the astronomer aligned with viewing end of the telescope.
;Background & Development
The observatory institution the
Astrophysical Observatory Potsdam (AOP) was founded in 1878.
The observatory started off with various instruments including a 30 cm (~11.8 in.) refractor by Schroeder and a 20 cm (8 in) Grubb.
A larger double telescope with a combination of visual and astrographic refractors was installed in 1889.
This had an aperture of 32 cm for photography, and a smaller 24 cm for visual work.
This telescope was used in support of the
''Carte du Ciel'', international astronomical project.
Other projects of the observatory include solar observations,
spectroscopy
Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. Matter wa ...
, and a
stellar luminosity
Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object over time. In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a st ...
catalog with many stars from the ''
Bonner Durchmusterung
In astronomy, Durchmusterung or Bonner Durchmusterung (BD) is an astrometric star catalogue of the whole sky, compiled by the Bonn Observatory in Germany from 1859 to 1903. The name comes from ('run-through examination'), a German word used for ...
'' (BD) .
In the mid-1800s the principle of
Doppler frequency shifting was discovered, and the next step was to apply this to changes in frequency of light, and further enhancement was achieved with photographic spectroscopy.
The 30 cm Schrodeder telescope was used to take the
spectrum
A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors i ...
of stars photographically, and the observatory became known for its work on stellar spectrographs. By 1892, they published a list of 52 photographic-based radial velocities from
spectroscopy
Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. Matter wa ...
.
However, with this they ran out of stars that could be observed with photographic spectroscopy using the 30 cm (12 inch) Schroder.
A bigger telescope would be needed to expand this area of study.
Major discoveries that the observatory was recognized for, were determining that
Spica
Spica is the brightest object in the constellation of Virgo and one of the 20 brightest stars in the night sky. It has the Bayer designation α Virginis, which is Latinised to Alpha Virginis and abbreviated Alpha Vir or α Vir. Analys ...
was
spectroscopic binary
A binary star is a system of two star, stars that are gravity, gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separa ...
in 1878, and also breakthrough on understanding of
Algol
ALGOL (; short for "Algorithmic Language") is a family of imperative computer programming languages originally developed in 1958. ALGOL heavily influenced many other languages and was the standard method for algorithm description used by the ...
.
Also, while the newer 32 cm
astrograph
An astrograph (or astrographic camera) is a telescope designed for the sole purpose of astrophotography. Astrographs are mostly used in wide-field astronomical surveys of the sky and for detection of objects such as asteroids, meteors, a ...
was felt to be adequate for photography, the director of the observatory was unhappy with its performance in spectroscopy.
Thus planning for a larger instrument, and a building to house it was undertaken in the 1890s.
In 1895 a new instrument for the observatory was approved.
;Design & Construction
The overall telescope was built by Repsold.
Repsold was a German optics company started by the astronomer
Johann Georg Repsold
Johann Georg Repsold (19 September 1770 – 14 January 1830) was a German astronomer and fireman. He began to make astronomic instruments mainly for his own use and his third son Adolf Repsold went on to establish a well-known astronomical i ...
, and made various optical instruments until 1919; they were based out of
Hamburg
(male), (female) en, Hamburger(s),
Hamburgian(s)
, timezone1 = Central (CET)
, utc_offset1 = +1
, timezone1_DST = Central (CEST)
, utc_offset1_DST = +2
, postal ...
.
Both objectives were figured by Steinheil from glass blanks made by Schott.
Steinheil was a German optics company founded by
Carl August von Steinheil
Carl August von Steinheil (12 October 1801 – 14 September 1870) was a German physicist, inventor, engineer and astronomer.
Biography
Steinheil was born in Ribeauvillé, Alsace. He studied law in Erlangen since 1821. He then studied astronomy i ...
.
The two objective lenses were completed by the firm Steinheil of Munich, figured from glass blanks made by Schott in Jena.
The 50 cm was designed optical for the human visual range, and was intended as a guide for the photographic telescope.
The visual 50 cm was regarded as satisfactory, although Bernard Scmdit adjusted the lens figuring in 1911 and 1914.
The 80 cm was found to have some
chromatic
Diatonic and chromatic are terms in music theory that are most often used to characterize scales, and are also applied to musical instruments, intervals, chords, notes, musical styles, and kinds of harmony. They are very often used as a pair, ...
errors and
Astigmatism
Astigmatism is a type of refractive error due to rotational asymmetry in the eye's refractive power. This results in distorted or blurred vision at any distance. Other symptoms can include eyestrain, headaches, and trouble driving at nig ...
, that lead to some refiguring of the optics in following years, as well as development of a new optical test.
;First light & Beyond
![PSM V58 D020 Photographic refracting telescope at potsdam](https://upload.wikimedia.org/wikipedia/commons/e/eb/PSM_V58_D020_Photographic_refracting_telescope_at_potsdam.png)
The telescope was inaugurated in August 1899 with attendance by
Kaiser Wilhem II
Wilhelm II (Friedrich Wilhelm Viktor Albert; 27 January 18594 June 1941) was the last German Emperor (german: Kaiser) and List of monarchs of Prussia, King of Prussia, reigning from 15 June 1888 until Abdication of Wilhelm II, his abdication on 9 ...
.
There was also an address by Director Vogel at the dedication.
The
Hartmann test was developed in response to the need to test the 80 cm objective lens, and this test became a famous way to test the optical properties of instruments in the 20th century. The telescope had a problem being used for spectroscopy and Hartmann developed the mask test to identify the issue with the main objective lens; this led to the lens being refigured to help the problem.
Inaugural instruments for the telescope included two spectrographs.''
''
In 1904, one of the discoveries made using the telescope was of the
interstellar medium
In astronomy, the interstellar medium is the matter and radiation that exist in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, as well as dust and cosmic rays. It fills interstella ...
.
The astronomer
Professor Hartmann determined from observations of the binary star
Mintaka
Mintaka , designation Delta Orionis (δ Orionis, abbreviated Delta Ori, δ Ori) and 34 Orionis (34 Ori), is a multiple star system some 1,200 light-years from the Sun in the constellation of Orion. Together with Alnitak (Zeta Orio ...
in Orion, that there was the element
calcium
Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to ...
in the intervening space.
The telescope was damaged during World War II, but repaired in the early 1950s.
Astronomical science work with the telescope was concluded in 1968, after which there was only basic upkeep for a long time.
In 1983 the building was recognized as a historical monument.
A foundation for preservation and function of the Great Refractor was founded in 1997, and with a considerable donation the telescope and site were refurbished with increased quality and made available for public observation programmes.
The organization that organized this was called ''Förderverein Großer Refraktor Potsdam e.V.,'' working in coordination with the observatory and benefactors. ''
''
The Great Refractor building is also noted for storing a collection of thousands of photographic plates.
These photographic plates, which in some cases date back to the late 19th century, are valued in modern times for software driven searches.
(see also
precovery
In astronomy, precovery (short for pre-discovery recovery) is the process of finding the image of an object in images or photographic plates predating its discovery, typically for the purpose of calculating a more accurate orbit. This happens mos ...
)
In May 2006, the telescope and facility were reopened after an extensive refurbishment of the telescope and dome mechanisms.
This included the dismantling of the great refractor in Jena by an engineering team.
In addition, important mechanical parts of the facility needed for operation of the telescope, such as the dome mechanism, were restored.
In 2017, after a year of restoration work on the dome and building, the Great double lens telescope facility was re-opened.
In 2019, the double refractor building hosted a reception for dignitaries, including Dutch royals, politicians, and bureaucrats from various organizations.
Dome and site
![Großer Refraktor-Detailaufnahme](https://upload.wikimedia.org/wikipedia/commons/1/1c/Gro%C3%9Fer_Refraktor-Detailaufnahme.jpg)
The moving weight of the telescope is 7000 kg (7 (metric) tons), and the dome weighs 200 (metric) tons (200 000 kg).''
''
The dome is constructed primarily of iron and wood, with the iron component manufactured by Bretschnieder and Kruger, while the wood was from Joester of Potsdam.
The dome could be rotated around in five minutes by
electric motor
An electric motor is an Electric machine, electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a Electromagneti ...
s, but it also had a manual turning option.
The electric controls could be operated near where the observer would be.
Also the entire floor could be rotated along with the dome to keep the observer aligned with the telescope.
The interior floor was done by Hoppe and the electric drive systems by Siemens & Halske.
The new dome was built in the style of the existing buildings, which had been designed by P. Spieker.
Two concepts for the new building were to have harmony with the older buildings and have the same design style.
The telescope and its dome were erected in Telegraph Hill (''
Telegrafenberg
The Einstein Tower (German: ''Einsteinturm'') is an astrophysical observatory in the Albert Einstein Science Park in Potsdam, Germany built by architect Erich Mendelsohn. It was built on the summit of the Potsdam '' Telegraphenberg'' to house ...
),''. Today the building is located in
Albert Einstein Science Park The Albert Einstein Science Park is located on the Telegrafenberg hill in Potsdam, Germany. The park was named after the physicist Albert Einstein. The best known buildings in the park are the Einstein Tower, an astrophysical observatory that was b ...
.
Spectrographs
Two new spectrograph instruments were developed for the Great double refractor.
There was a larger one that used three
prism
Prism usually refers to:
* Prism (optics), a transparent optical component with flat surfaces that refract light
* Prism (geometry), a kind of polyhedron
Prism may also refer to:
Science and mathematics
* Prism (geology), a type of sedimentary ...
s, with the prisms made by Steinheil.
The spectrograph weighed 31 kg, and was installed on the end of the telescope.
The other spectrograph weighted 20 kg, but only had a single prism made by Zeiss in Jena.
An
ultraviolet
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...
spectrograph was commissioned by the observatory and built by Toepfer and Son, however the 80 cm was limited to 360 nm wavelength light.
''Astronomical Spectrographs and Their History'' reports that the instrument worked in the lab down to 285 nm.
See also
*
List of largest optical refracting telescopes
Refracting telescopes use a lens to focus light. The largest refracting telescope in the world is the Yerkes Observatory 40 inch (102 cm) refractor, used for astronomical and scientific observation for over a century. The Swedish 1-m S ...
*
List of largest optical telescopes in the 20th century
The following is a list of the largest optical telescopes in the 20th century, paying special attention to the diameter of the mirror or lens of the telescope's objective, or aperture. Aperture rank currently goes approximately by the usable physi ...
*
Leibniz Institute for Astrophysics Potsdam
Leibniz Institute for Astrophysics Potsdam (AIP) is a German research institute. It is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Observatory Potsdam (AOP) founded in 1874. The latter was the world's first o ...
*
Einstein Tower
The Einstein Tower (German: ''Einsteinturm'') is an astrophysical observatory in the Albert Einstein Science Park in Potsdam, Germany built by architect Erich Mendelsohn. It was built on the summit of the Potsdam '' Telegraphenberg'' to house ...
(A nearby solar observatory and historical structure, erected 1924)
*
References
External links
{{commons category, Großer Refraktor (Potsdam)
Photo Gallery by AIP
Optical telescopes
1899 establishments in Germany
Potsdam
Great refractors
Double telescopes