Essential Architecture-  Berlin

Observatory in Berlin

architect

Karl Friedrich Schinkel

location

The external view of the Observatory, in An der Sternwarte (Rosa Luxembourg Strasse), is fairly constricted, although it could be combined with a visit to the adjacent Babelsberg Park, on the banks of the Havel river.

date

1835

style

Greek Revival

construction

stone

type

observatory
 
  Painting by Freyendanck, 1838
 
   
The Berlin Observatory has its origins in 1700 when Gottfried Leibniz initiated the Brandenburgische Society which would later become Prussian Academy of Sciences. Although the original observatory was built in the outskits of the city, over the course of time the city expanded such that after two centuries the observatory was in the middle of other settlements which made making observations very difficult and a proposal to move the observatory was made. The observatory was moved to Babelsberg in 1913.

 
The refractor
by Joseph von Fraunhofer
in the Scientific Instruments exhibition

Gerhard Hartl

Click for larger photo

The refractor

The discovery of the planet Neptune
Astronomical telescope by Fraunhofer

Imagine we are living in the 1820s. Among the large and powerful instruments in astronomy, reflecting telescopes were still more important than refractors. Forty years earlier, on 13th March 1781, Friedrich Wilhelm Herschel (1738-1822) had discovered the planet Uranus, and shortly after this he had built his giant telescope (free refractor diameter 1.2 metres). The difficulties in building refractors of similar strength seemed insurmountable: the glass technology for the production of sufficiently large objective lenses was not controllable before Fraunhofer. Mounting large astronomical telescopes parallactically was another problem that had not been solved by that time. For such mounting, the mechanical system of the telescope is designed in such a way that one axis - the polar axis - is aligned in parallel with the rotational axis of the earth. If the telescope is swivelled around this axis against the rotation of the earth by means of a clockwork mechanism, the telescope is constantly directed to a particular point in the sky. Before Fraunhofer, nobody had succeeded in moving the heavy mass of a large telescope with the necessary precision.

Fraunhofer sets new standards



Joseph von Fraunhofer, optician and physicist, 1787-1826

Joseph von Fraunhofer (1787-1826) initiated a development that was to produce large, powerful refractors mounted parallactically. By improving the quality of the optical glass, he succeeded in producing larger achromatic objective lenses of the appropriate grade (homogenous glass body, free from reams and bubbles). The glass required for this purpose was produced in the glassworks at Benediktbeuern by Pierre Louis Guinand (1748-1824). From 1814 onwards, the objective diameters of the telescopes manufactured in his optical institute in Munich became larger and larger. Therefore, it must have been especially welcome and represented a special challenge to Fraunhofer when the astronomer Friedrich Wilhelm Georg von Struve (1793-1864), leader of the observatory of Dorpat (today Tartu, Estonia), ordered a large, parallactically-mounted refractor for his institute. Fraunhofer began designing it in 1818. The work lasted until 1824. With the Dorpat refractor, Fraunhofer had created the model of all large parallactically-mounted refractors. Every time the glass was melted, Fraunhofer had to travel the 50 kilometres between Munich and Benediktbeuern. On his way back to Munich in late summer of 1825, he used a raft to cross the River Isar and caught a bad cold which caused tuberculosis to break out. On 7th June 1826 Joseph von Fraunhofer died, only 39 years of age. However, the technical know-how for building astronomical observation and measuring instruments of a size and power unthinkable at the time was preserved in his institute.

After his return in 1827 to Berlin from a five-year expedition through the South American continent, Alexander von Humboldt (1791-1855) strongly supported the construction of a state-of-the-art observatory in Berlin. From the Prussian King Friedrich Wilhelm III he obtained permission to order a large refractor from the Fraunhofersche Werkstätte (Fraunhofer Workshops), and a new Royal Observatory was built at the Hallesches Tor (Halle Gate) by Karl Friedrich Schinkel (1781-1841).



Royal Observatory Berlin, constructed 1832-1835 according to the plans by Friedrich Schinkel, exterior view of around 1873.

The discovery of a new planet - Neptune

In 1781, W. Herschel had discovered Uranus, the first planet of our solar system, and one not visible by the naked eye. When it was certain that it really was a new planet, scientists set out to calculate its orbit. Also, the new planet fitted well into a special arithmetical relation that had been established by the Wittenberg Professor Johann Daniel Titius (1729-1796), and which is known as the Titius-Bode series: the mean distances of the planets to the sun follow a ratio of integers:

Mercury 4 + 0 = 4
Venus 4 + 3 = 7
Earth 4 + 6 = 10
Mars 4 + 12 = 16
(Planetoids) 4 + 24 = 28
Jupiter 4 + 48 = 52
Saturn 4 + 96 = 100
(Uranus) 4 + 192 = 196
(Neptune) 4 + 384 = 388


From this ratio of numbers, which did not have an upper limit, Johann Elert Bode (1747-1826), the director of the Berlin observatory, came to the assumption in 1784 that there might be more planets outside the orbit of Uranus.

In 1821, Alexis Bouvard (1767-1843) drew up new, improved tables of the planets, with indications of the time-dependent locations of the planets Jupiter, Saturn and Uranus. These tables reflected the theory of the influence of the planets on each other in their movements through gravitational fields. Up to 1790, calculations had corresponded well with actual observations. However, for observations made after 1790, differences increased rapidly. These differences could only be explained if one assumed the existence of another planet whose gravitation was causing these disturbances. Despite the enormous complexity of these calculations, some astronomers dedicated themselves to this problem. On 1st June 1846, Urbain Jean Joseph Leverrier (1811-1877) submitted his work to the Academy of Paris. In this work he indicated the position of an unknown planet that would supposedly disturb the orbit of Uranus on 1st January 1847. This position of the planet was calculated based on theory.



Johann Gottfried Galle (1812-1910), observer at the Royal Observatory in Berlin.

On 23rd September 1846 Johann Gottfried Galle received a letter in the Berlin observatory, in which Leverrier presented the following request: "Today I wish to request the untiring observer that he dedicate some moments to scanning a region of the sky where a planet may be discovered. It is the theory pertaining to the planet Uranus that has led me to this hypothesis." He probably turned to Galle because no colleagues at other observatories had followed up on his suggestion, first made in June 1846. Also, the Fraunhofer refractor represented a first-class instrument and was available in Berlin. What happened the following night is reported in the Astronomische Nachrichten (News in Astronomy) published on 12th October: "In the same night, Mr. Galle compared the excellent map drawn by Dr. Bremiker...with the sky and, very close to the location specified by Mr. le Verrier, he discovered almost immediately a star that was missing on the map." The eighth planet in the solar system had been discovered.

http://www.deutsches-museum.de/e_inhalt.htm
 
Berlin Observatory

The 150th. anniversary of the discovery of Neptune in 1996 brought a certain amount of attention to Berlin Observatory. In reality, the history of astronomy in Berlin encompasses more than the Neptune discovery, and even today there is much of interest there for the visitor who is also an amateur astronomer.

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Berlin Observatory
The Observatory where Neptune was discovered exists no more. It lay in the Kreuzberg area just south of present-day Checkpoint Charlie and was moved to the Potsdam suburb of Babelsberg, a district better known for the UFA (now DEFA) film studios, where films like The Blue Angel, Metropolis and Baron von Munchhausen were made. Close by is the Potsdam Astrophysical Laboratory, home of the Einstein Tower, this observatory being more accessible for public viewing. Since 1991, the two insitutions have been united as the Astrophysical Institute Potsdam.

The Observatory building in Kreuzberg was actually the Observatory's second home. The Observatory, as an organization, was originally inaugurated in 1700 in connection with the founding of the Brandenburg Society under the direction of the famous mathematician Leibniz, and has the distinction of being the oldest-existing observatory ( i.e. as an institution ) in "Germany". The first Observatory building came into service in 1711 and was based in present-day Dorotheenstraße .

In 1700 Germany did not actually exist as an entity and Berlin was a much less important town than it became later. The founding of the society was possibly all part of the first indications of Berlin's new confidence in itself as a city. In 1700 it was the capital of the state of Brandenburg, part of the Holy Roman Empire. By 1763 Brandenburg had become Prussia, a fully independent and enlarged state which continued to expand and became the state around which German unification was achieved in 1871. Leibnitz's society had, along the way, become the renowned Prussian Academy of Sciences.

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Johann Elert Bode
Johann Elert Bode was appointed to the Observatory in 1772. His name is well known because of Bode's Law although this relation was either a) actually discovered by Johann David Titius of Wittenberg with Bode just spreading the word about the discovery, or b) Bode had discovered it independently. It all depends on which source you consult. This law, ironically, was discredited by Berlin's later discovery of Neptune.

If you divide the distance from the Sun to Saturn into 100 lengths, then

Mercury is at 4 lengths

Venus is at 7 lengths (4+3)

Earth is at 10 lengths (4+6)

Mars is at 16 lengths (4+12)

Nothing was seen at 28 lengths (4+24)

Jupiter is at 52 lengths (4+48)

Saturn is at 100 lengths (4+96)

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Bode became enthusiastic about trying to find the 'missing planet' at 28 lengths. He became a member of what was known as the 'Celestial Police' which attempted to find this object, and then (after being pre-empted by Piazzi discovering Ceres before he was actually informed that he himself was a member of the 'Celestial Police') became instrumental in searching for asteroids - the total mass of these asteroids turning out to be insufficient to have originated from the single planet that was expected from Bode's Law.

He became director in 1786, a post he kept until 1826. During the 40 years of his directorship, Berlin became recognized for its observations of planets, double stars and comets.

In 1779, he discovered what is now M64, the Blackeye Galaxy, one of the brightest galaxies in the Virgo Cluster.

In 1781 Bode had suggested the name Uranus for the planet discovered by William Herschel, although this name was not fully adopted in Britain until 1850. He also discoverd that uranus had previously been unwittingly noted by Tobias Mayer in 1756 and John Flamsteed in 1690. These prior observations proved useful for calculating Uranus's orbit - it very soon became obvious that Uranus was deviating from these predictions of its orbit.

In 1774 he had founded the Berliner Astronomisches Jahrbuch (and compiled 51 annual issues). In 1801 he produced Uranographia, a collection of twenty star maps and a catalog of 17,240 stars and nebulae, 12,000 more than had appeared in earlier charts. Whereas previously star charts had only indicated the brighter stars, the Uranographia was the first reasonably complete depiction of the stars visible to the unaided eye. It included an early use of constellation boundaries, a concept accepted and refined by 19th-century cartographers

He produced a catalog of nebulae containing 75 objects in 1777 and 77 in 1780 (containing 50 "true" deep sky objects and 5 personal discoveries): "A Complete Catalogue of Hitherto Observed Nebulous Stars and Star Clusters".

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Johann Franz Encke
The original choice for Bode's successor in 1826 was Bessel but he preferred to stay in Königsberg. The job was given to a former pupil of Gauss, Johann Franz Encke.

An important event in this period had been the establishment in 1809 of Berlin University by Alexander von Humboldt (latterly the Humboldt University in East Berlin). Humboldt himself persuaded the King both to purchase three large telescopes (including the Fraunhofer-Refraktor used to discover Neptune) and to finance the building of a urgently-needed new observatory :- in the area between Lindenstrasse and Friedrichstraße, Kreuzberg. There is nothing to mark the exact spot where the observatory was actually situated, but the existence of an Enckestraße in the area provides a certain legacy. The basic plans were drawn up by Encke and carried out by the famous architect Schinkel, who was responsible for many of Berlin's public buildings, opening in 1835. The former observatory in Dorotheenstraße served for a time as a station on the optical telegraph connected to the Rheinland and was finally demolished in the early years of this century to make way for the building of the State Library on Unter den Linden.

The main instrument was a 9'' Fraunhofer refractor. It had an 8 meter rotatable dome, and the basement was split between living quarters and a working observatory section.

Encke was to establish Berlin as a leader in the field of minor planets. He concentrated on the calculation of the orbits of asteroids, and the large planets' influence on them.

For approximately 30 years up to 1859 he was engaged in the drawing up of the new star charts which had been the task of a commission set up by Bessel but which were largely carried out under the leadership of Encke. These charts were soon improved upon by charts produced by Argelander, the director of the Bonn Observatory (Bonn Durchmusterung), but nevertheless were invaluable in Encke's work on minor planets and were also an aid in the discovery of Neptune on the 26. September 1846.

He published 37 volumes of the 'Berliner Astronomisches Jahrbuch' (1830--66), along with his assistants, J.P.Wolfers and Bremiker.

Encke's name is well-known today because of Encke's comet. This was actually discoverd for what it was in 1818 by Jean Louis Pons of Marseille (and had, as it turned out, also been seen by Pierre Mechain in 1786 and Caroline Herschel in 1795, as well as Pons himself in 1805). In early 1819, Encke calculated its orbit, and its period - 3,3 years, the shortest period of any known comet. It was particularly sensational at the time because no comets were known with a period of less than 70 years. Encke's Comet is one of the few comets which are not named after their discoverer.

It's return in 1822 was only observable in the Southern Hemisphere, but was observed by Gauss in 1825, from the Seeberg Observatory, near Gotha, where he was working at the time.

On previous observations, the orbit was seen to be slowing by 2-3 hours, which Encke attempted to explain by proposing an interstellar ether. It is now known that the orbit is affected by the loss of material as the comet approaches the Sun. The comet is the source of the Taurid meteor shower.

In 1823, Encke had used information from the Transits of Venus of 1761 and 1769 to calculate a distance to the Sun of 153.303 million kilometers ( cf. modern value of 149.598 million kilometers ). In 1837 he discovered Encke's Gap, in Saturn's ring A - this Division is now known to be 270 km. wide. Under good seeing conditions, this ring can be seen at either end of the rings, but not all the way around.


rings and satellites of Saturn

Encke's gap is now known to be caused by a satellite - Pan. This satellite has a diameter of 20 km, and its gravitational effect maintains the gap at 270 kms wide, and causes wavelike disturbances in the ring either side of the gap. This satellite was only discovered in 1990, after a computer search of Voyager images taken a decade earlier, although its existence had been predicted earlier.

Encke had been appointed Professor in Astronomy at Berlin University in 1844, and remained in this post until 1863. He was still Observatory Director at the time of his death in 1865.

Although the observatory was later demolished, the square adjacent to its site is still known as Enckeplatz (since 1844).

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Johann Friedrich Galle
Encke was given an assistant for the new Observatory and the post was filled by Johann Friedrich Galle. In 1845, Galle sent his doctoral thesis to Le Verrier, director of the Paris Observatory, and Le Verrier had sent back details of his calculations of a new planet based on perturbations of Uranus. Within one hour of starting a search for this planet, on 23. September 1846, Galle and his colleague Heinrich d'Arrest had found the planet, 8 minutes of arc away from the predicted position (they had found it because it was absent from Encke's charts). The Fraunhofer telescope used to discover Neptune is now on display in the Deutsches Museum, München.

Apparently, Galle was also the first to identify the Crepe ring (Ring C) around Saturn, in 1838, although it was forgotten and re-discovered independently a few years later. In 1875, although by this time at Breslau, he was the first person to use an asteroid (Flora) to measure the distance to the Sun, calculating a value of 148.290 million kilometers.

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Heinrich D'Arrest


Soon after his part in the Neptune discovery, he discovered Comet D'Arrest on June 28. 1851, while working at the Leipzig Observatory. It was described as very faint. The comet was not found on the next night because the sky was too hazy, but on June 30, d'Arrest described it as large and faint.

The Comet has the designation 6P, and has a period of 6.2 years.

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Discovery of Neptune
The Berlin discovery is covered directly above, under Galle and D'Arrest.

A couple of weeks later (by October 10), the main satellite of Triton was discovered in Liverpool by William Lassell. It is a matter of conjecture as to whether Lassel could have found the planet himself if he had acted differently.

If we are to take the words of a few ex-Cambridge University graduates at face value, they 'cherish' the memory of Professor Challis, who 'probably' saw Neptune before the Germans but didn't realise it, and through a comedy of errors (and/or incompetence) failed to look carefully where the British mathematician John Couch Adams had told him to.

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Johann Heinrich Mädler

Mädler was never officially a full employee of the Observatory but he was effectively used by Encke in such a capacity. He had previously made a considerable number of observations at the private Observatory owned by the Berlin banker, Wilhelm Beer.

By 1830-32 Beer and Mädler had produced the first reasonably good charts of Mars. They had adopted the feature with the current name of Sinus Meridiani as their zero of longitude - today the zero is fixed as the center of a crater called Airy in the Sinus Meridiani ( the craters of Beer and Mädler also lie close to the meridian ). They were the first to report a dark band around the periphery of a shrinking polar cap and also recorded seeing streaks, which could have been the same streaks designated later as 'canali' by Schiaparelli (and misinterpreted as 'canals' by a few other people). The picture below shows their map of 1840.

Herschel had tried to measure the rotation period and his observations were re-worked by Beer and Mädler yielding a period of 24 hours 37 minutes 23.7 seconds, which is only one second in error ( should be 22.6 seconds ).

During 1834-6, Beer and Mädler published their Mappa Selenographica ( Der Mond nach seinen kosmischen und individuellen Verhältnissen oder allgemeine vergleichende Selenographie ), one of the best moon maps to appear until then (held by many to remain unsurpassed until 1878), and Der Mond (1837) , a classic on lunar research.

Both astronomers are mentioned briefly in Jules Verne's work 'From the Earth to the Moon'.

In 1836, Encke appointed Mädler as an observer at the Berlin Observatory, and here he continued his work on planets, and also studied double stars. In 1840 he moved to Dorpat as director of the Observatory.

Wilhelm Foerster

Wilhelm Foerster had been appointed a second assistant in 1855 and in 1865 he succeeded Encke as director. He modernised the Observatory, promoted the founding of Potsdam Astrophysical Observatory and founded the Urania Society to promote popular interest in Science.

In 1860, he discovered the asteroid Erato, the 62nd. asteroid to be discovered.

During the DDR-period, he received especial mentions for his anti-Bismarck stance, particularly during the period of the anti-socialist laws at the end of the 19. century. When the First World War broke out, he appealed to the government, along with Einstein, to cease hostilities.

Hermann Struve
The increasing size of Berlin made observations at the Berlin Observatory in Kreuzberg more difficult and Foerster attempted to persuade the government to finance a new building. However he retired in 1903 and the observatory actually moved to Babelsberg during the directorship of Struve.

Hermann Struve was a third-generation member of the famous family which had effectively controlled Pulkovo Observatory, near St. Petersburg, since its inception. Hermann had become director of Pulkovo, but moved to Germany, going first to Königsberg, and then Berlin. He was an expert on Saturn .and its ring system (contributing greatly to the modern theory of the movement of the satellites of Saturn), and studied other solar-system objects, as well.

The land for the new observatory was situated at the eastern end of Babelsberg Park and was provided free, the sale of the old observatory providing the money for construction and instrumentation. This old observatory was demolished.

The new observatory came into service in 1913. The central dome was occupied by a new 65 cm. refractor, delivered in 1914, the first big astronomical instrument manufactured by Carl Zeiss Jena. When a 120 cm. reflecting telescope was installed in 1924 (being delayed because of the war), Berlin could claim to be the best-equipped observatory in Europe.

His brother was also a professor of astronomy and director of Charkow observatory.

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Postwar
After the Second World War, the Observatory came again under the control of the (now DDR) Academy of Sciences after being, since 1919, under the full control of the University. However many of its instruments were shipped off to the Soviet Observatories of Pulkovo and Simeis to compensate for damage caused to these observatories by the Nazis (including the 120 cm. reflecting telescope).

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Location
The external view of the Observatory, in An der Sternwarte (Rosa Luxembourg Strasse), is fairly constricted, although it could be combined with a visit to the adjacent Babelsberg Park, on the banks of the Havel river.

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Potsdam Astrophysical Observatory
The new science of Astrophysics came into being in the later half of the 19. century, pioneered by Kirchoff and Bunsen in Heidelberg, and the first institution in the world specifically dedicated to this new science was the Potsdam Astrophysical Observatory, instituted in 1874.

Originally research was split between Potsdam town (under Spörer) and the Berlin Observatory in Kreuzberg (under Vogel) before the observatory building itself was finally finished in 1879. The building has three domes - the central dome contained the largest telescope, a smaller telescope was contained in the western dome, and the eastern dome contained Spörer's telescope and was used for solar research. The site chosen was on the Telegrafenberg, on the south side of Potsdam, to allow a clear view southwards. The hill had received its name because it was previously the site of a relay station on the optical telegraph to Koblenz.

It was originally planned that Gustav Kirchoff would be the director of the Astrophysical Observatory. He had been appointed professor of Mathematical Physics at Berlin University but turned down the post of director at Potsdam. For a short period the observatory was run by a committee before the appointment of Hermann Carl Vogel as director in 1882.


From 1890, plans were laid for a larger telescope to study weaker objects and in 1899, the Observatory started using this Great Refractor , actually a double refractor with lenses of 80 cm. and 50 cm, housed in a separate building and which, at that time, was the largest refractor in the World, mounted in a 24 m. diameter dome. A reflector was really required but the technology of the time could not deliver a suitable instrument. Furthermore the refractor produced disappointing results initially but was improved greatly by modifications carried out in 1914 by the as-yet-unknown optical worker, Bernhard Schmidt. Simultaneous with these developments, an adjacent residential building was modified as a solar observatory.

Hermann Carl Vogel


Vogel came to Potsdam in 1879, and from 1882 he was its Director, remaining so until 1907.

In 1871, before coming to Potsdam he had made the first observations of Doppler Shifts at opposite limbs of the Sun, confirming the solar rotation that was strongly inferred by the motion of sunspots

Vogel and Julius Scheiner are usually credited as being the first person to successfully use the Doppler shift to measure the radial velocities of stars - their work in this field caused a sensation in astronomy. Between 1888 and 1892, reliable Doppler Shifts for fifty stars were obtained (previous work had been attempted from 1868 onwards by William Huggins in London and Angelo Secchi in Rome).

In 1883, he published the first catalog of stellar spectra, and in the course of analying stellar spectra he had discovered spectroscopic binaries, being able to calculate properties such as the diameter of the binary system and its individual components, the orbital velocity and total mass of the system.

In 1889 E.C. Picker ing. of Harvard Observatory, had noticed spectral shifts in Mizar (of the Mizar-Alcor system) which could be explained by it being a binary star. A few months later Vogel noticed analogous shifts in Algol, although this time the companion was too faint to record a spectrum

Gustav Spörer
Spörer was born in Berlin on 23/10/1822. He had already been active in solar research in Berlin for some time and indeed the idea of an Astrophysical Observatory grew out of plans to build a solar observatory under his leadership.

He had earlier, in 1861, discovered a law concerning the variation in latitude of sunspot zones over the course of a solar cycle - Spörer's law - At the start of a cycle, spots occur at latitudes between 30 and 45 degrees. As the cycle progresses, spots appear closer to the equator until, at maximum, the average latitude of the groups is about 15 degrees. After maximum the spots become less common but still approach the equator reaching about 7 degrees. They die out before reaching the equator but, before they do so, spots of a new cycle are seen at higher latitudes. The effects of Spörer's Law can be displayed in a "Butterfly Diagram", although this diagram was only introduced later, by Maunder.

He also independently discovered the Maunder Minimum - a period between 1645 and 1715 when sunspots were virtually non-existant.

A.A. Michelson
A notable event occured in 1881, when Michelson attempted his first reliable experiment to detect the Earth's motion with respect to the ether, in the cellar under the eastern dome. His continual lack of success in detecting any motion in this and later experiments in America led eventually to the overthrow of the ether theory - and towards the Special Theory of Relativity.

Johannes Franz Hartmann
Hartmann had presented his doctoral thesis in Leipzig in 1891 on the Earth's shadow during moon eclipses (Die Vergrösserung des Erdschattens bei Mondfinsternissen). He worked in Wien, Austria, with de Ball and again in Leipzig with Bruns.

In 1896 he moved to Potsdam were he worked with H.C. Vogel and was promoted to 'Observer' in 1898 and to 'Professor' in 1902. During these years he became one of the leading astrophysicists of his time. His main work was on defining standards for wavelengths as well as in instrumentation (microphotometer). During this time the big refractor with a diameter of 80 cm was installed and Hartmann found the photographic telescope to be useless: the lenses were not good enough. Then he developed a method of testing telescope lenses, which is today named after him. After refiguring the main lens according to his recommendations the telescope was in good condition and went to work.

Hartmann found clouds of Calcium with this instrument during his spectrographic work. He found that Ca II absorption lines in the spectrum of the binary star δ Orionis failed to take part in the periodic oscillations of the other lines. He eventually that this was due to interstellar gas, an original concept at the time. Although receiving support from V.M. Slipher in 1909, Hartmann’s interpretation was not accepted immediately. In 1926, Eddington was able to produce conclusive support for it.

In 1909 he went to Göttingen as Director of the Observatory and Professor at the University there. Since the observing conditions in Göttingen were not to his needs he went to La Plata in 1921, where he developed a theory on Novae and discovered that the minor planet Eros is not a spherical body.

Karl Schwarzschild
In 1909 Karl Schwarzschild succeeded Vogel as director. In addition to Astronomy, Schwarzchild was also active in the field of Theoretical Physics. He had come from Göttingen where he had been made a full professor at the age of 28 and was also the director of Gauss's old observatory there.

Unfortunately he contracted a fatal disease on the Russian front during the war and died in Potsdam in May 1916, not before producing the work for which he is most famous i.e finding the first exact solution to Einstein's Field Equations - for the case of a gravitational field of a point mass in empty space - the Schwarzschild Solution (which therefore describes the field around a static black hole).

At almost the same time, while severely unwell, he had also produced important work in quantum theory. He was an early champion and great promoter of Nils Bohr's new quantum theory and had, in 1900, suggested that the geometry of space was not Euclidean.

Solar theory was one of his interests at Potsdam and in 1906 he explained solar limb darkening as being due to the fact that when we look at the center of the Sun, we are seeing into deeper and hotter layers. He took part in Potsdam's expedition to Tenerife in 1911 to study Halley's comet and studied the density and structure of its tail.

Ejnar Hertzsprung

In 1909, shortly after he arrived, Schwarzschild was joined by a colleague from Göttingen, Ejnar Hertzsprung, who stayed in Potsdam until moving to join De-Sitter in Leiden in 1919.

The first color-magnitude diagrams (an early version of the present-day Hertzsprung-Russell diagrams) to be published appeared in 1911, plotting stars of the Pleiades and the Hyades. Vogel had earlier attempted to classify stellar spectra, coming up with a scheme similar to the better-known scheme by Secchi - Vogel believed that his classification represented successive stages in stellar evolution, from young white stars to old red ones (an excusable error).The adjacent image is the Color Magnitude Diagram for the Hyades with magnitudes on the horizontal axis (absolute on top and 'absolute photographic magnitude' below, and color index on the vertical axis. These axes are the other way round to the current Hertsprung-Russell Diagram.

In 1911, he found that Polaris was a pulsating variable (i.e. a Cepheid). This had previously been assigned a magnitude of 2 and other stars assigned values relative to this, so Hertzsprung thereby showed Polaris to be an unreliable standard.

In 1913 he developed the method of distance determination using Cepheid variables, and used this method in an attempt to estimate the distance to the Small Magellanic Cloud (this was the first distance determination of an object outside our galaxy). Henrietta Leavitt had originally derived the Cepheid luminosity/period law by studying Cepheids in the SMC and made the realtion known in 1912. These clouds were not recognized at the time to be satellite galaxies of the Milky Way, but the assumption that all the stars within them were at more or less the same distance from Earth was nevertheless a valid assumption to make now and then. Leavitt did not identify the said stars as Cepheids - she said that ‘they resemble the variables found in globular clusters, dimishing slowly in brightness, remaining near minimum for the greater part of time, and increasing very rapidly to a brief maximum’. Hertzsprung showed they were similar to Cepheids and made the first attempt to calibrate Leavitt’s relation, i.e. to introduce absolute magnitude. Hertzsprung's estimate to the Small Magellanic Cloud was seriously in error because of the then unknown effect of dust absorption. (Shortly afterwards, Shapley made use of this relationship in a big way to derive distances to several globular clusters).

He developed a technique for observing double stars, using the Great Refractor, which eliminated errors to the extent that results were ten times more accurate than before.

Einstein Tower

Added in 1921/24, the 16 meter-high Einstein Tower is well known in its own right for being an example of expressionist architecture, being designed by the famous architect Erich Mendelsohn. Earlier, Schwarzschild had attempted (obviously unsuccessfully) to measure the redshift of Fraunhofer lines in the gravitational field of the Sun, as predicted in Einstein's theory, from the previously-mentioned solar observatory. The Einstein Tower was constructed to further research in this direction, thru the initiative of the physicist Erwin Finlay-Freundlich (who had been collaborating with Einstein, especially after Einstein had moved to Berlin in 1914 to work for the Academy of Sciences). Because of the sky-high inflation prevailing in Germany during construction, the original plan for reinforced concrete had to be abandoned and it was built in brick covered in plaster. The financing was dependent on private donations - the cost for the optical instruments was borne heavily by Carl Zeiss Jena. Needless to say, the tower had little success in its original purpose of detecting the gravitational red-shift but served as an important solar telescope in other work, for example - the measurement of magnetic fields in sunspots and investigations of the corona. It was severely damaged in a bomb attack of 14. April 1945 and it was some time before research was able to fully get started again.

Location
To reach the observatory you have to head southwards from the town center, towards a hill dominated by the Landtag (parliament) building (Potsdam is the capital of Brandenburg). You turn off the main road onto Albert Einstein Straße which, once you have eventually found it, takes you past the Landtag, and eventually to the Albert Einstein Scientific Park. There is a small kiosk if you require any information, and a small climb takes you to where the three main buildings of the Astrophysical Observatory are grouped together. In this out-of-the-way setting, it seems incredible that the Observatory should have suffered a direct hit from a bomb.

Miscellaneous
Starting from the second half of the 19th century, stellar magnitudes were revised to correct the crude methods that had existed up to then. A precise investigation at Potsdam resulted in the Potsdamer Photometrische Durchmusterung by G. Müller and P.Kempf. In full - 'Photometric Catalog of the Northern Sky, Containing the Magnitudes and Colors of all Stars of the B.D. to Magnitude 7.5' (Photometrische Durchmusterung des Nördlichen Himmels, enthaltend die Grössen und Farben aller Sterne der B.D. bis zur Grösse 7.5)

H. Ludendorff determined an orbital period of 27.1 years for the eclipsing binary ε Aurigae, soon after an eclipse of 1900-1902.

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University Research
There is a Department of Astronomy and Astrophysics at the Technical University of Berlin. Apart from their main observatory in Dahlem, they have a satellite station based in the Wilhelm-Foerster-Observatory.

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Other Research
The eastern suburb of Adlershof is one of the two bases ( the other is in Stuttgart) of the DLR Institute of Planetary Research (DLR being the national aviation and space research body). This Institute has responsibility for the cameras on the Mars 96 mission.

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Special thanks to http://bdaugherty.tripod.com/astronomy/berlin.html

links

 
www.essential-architecture.com