Hamburg Observatory - Overview:
Buildings & Telescopes
The 1m Reflector Telescope at Hamburg Observatory is, by merit of its Zeiss
mounting, one of the most unusual constructions among telescopes. Prior to
1920, and again between 1946 and 1960, it was the largest telescope in Germany. A very
similar 125cm reflector telescope of Berlin Observatory (Babelsberg) surpassed the
1m Reflector in the years 1920 - 1946, however, that instrument was dismantled, and
transported to the former Soviet Union after World War II as part of the reparations
(where it is still in use at Crimean Observatory).
When the relocation of Hamburg Observatory to Bergedorf took shape at the beginning of
this century, and future instrumentation had to be chosen, the large refractors were
at the peak of their development. With the rise of astrophysics, however, reflector
telescopes had become increasingly important.
In new observing techniques like celestial photography in particular, they were superior
because of their larger focal ratios and absolute lack of
chromatic aberration. Although some remarkably large reflectors had been built in
the 19th century (Birr Castle: 1.80m, Malta: 1.20m, Melbourne: 1.22m), little success
was assigned to them, due to their heavy, difficult to polish, metal mirrors.
Only after L. Foucault had been able to prove the usefulness of silver-coated
glas mirrors for astronomical purposes, and by merit of the
excellent exposures made by J. E. Keeler at the turn of the centuries with the 91cm
Crossley Reflector (Lick Observatory), did reflector telescopes start their triumph.
The Hamburg 1m Reflector was the world's fourth largest reflector at the time it
started to work in 1911 (after Mt. Wilson: 1.52m, Paris: 1.20m, Lowell-Obs. Flagstaff:
1.07m), especially since the metal reflector telescopes no longer existed or were - as
was A. A. Commons 1.52m reflector with glas mirror - no longer used.
The order to build the optical and mechanical components of the telescope, as well as
the 10m dome, went to Carl Zeiss in Jena. The astronomical section of that firm had
heen founded only a few years before in 1897. Prior to the Hamburg instrument, Zeiss
had delivered only two medium sized reflector telescopes to Heidelberg (72cm) and
Innsbruck (40cm). Thus the 1m Reflector was the first large Zeiss telescope.
It was the first telescope to be equipped with a Zeiss-mounting after Fr. Meyer.
In such a construction with its characteristic bars and counterweights, the
declination and right ascension axes are performed as hollow-axes. Inside,
rods carry the load of telescope and counterweights, while the weight on
the bearings of the axes themselves is reduced. A very exact and frictionless motion
was thus achieved. The telescope, despite its weight of 26 tons, is indeed easily
movable with one hand. Another advantage is that it can be moved across the
meridian without - as with a German Mounting - turning the telescope to the
Apart from the Hamburg 1m Reflector, only two further large reflector telescopes were
built with this kind of mounting: the above mentioned 1.25m telescope of Babelsberg
Observatory, and a twin of the Hamburg instrument which was delivered to the royal
Belgian observatory in Uccle (Brussels). Tube and optics of the Belgian telescope were
lost in world war II; the mounting was equipped with a new 84/120cm Schmidt
telescope in 1958.
The 1m Reflector was built as a Newton system with an extremely high focal
ratio (3m focal length). Access to the Newton focus was provided by a platform in
front of the dome opening which could be moved up and down, as well as into the dome.
Because of the extremely large focal ratio of 1:3, image distortion was naturally very
large. Pointlike stellar
images could be obtained only very close to the plate centre, however, fields up to
2 x 2 deg² have been successfully investigated. If necessary, the image quality could
be improved by reducing the aperture by means of an adjustable iris diaphragm
in front of the primary mirror. Tracking corrections could be made with the aid of an
off axis guiding eyepiece in the Newton focus, or with the guiding refractor (aperture
20cm, focal length 3.40m). A 10cm finder was also available.
Although the new building was completed in 1907, and the dome in 1909, the telescope
could not start operating before the end of 1911. Performance tests proved
unsatisfactory, and Zeiss had to make a new mirror cell because of irregular bending of
the 17cm thick prime mirror. These works took nearly a year so that regular
observations could start only in early 1913.
During its first years, the telescope was used mainly by the
director Richard Schorr and the Danish astronomer Thiele. Until 1920, these two
observers took more than 1700 photografic plates which were used primarily for the
search and position determination of comets and planetoids. 30 new asteroids and one
new comet (1918III Schorr) were found with the 1m Reflector in these years, and two
periodical comets were rediscovered.
In April 1920, young Walter Baade took over the telescope. Had the research
program been hitherto mainly concerned with classical astronomy, so now astrophysics
became more and more dominant. Baade took countless photographs of stellar clusters,
gaseous nebulae, and galaxies. Downright epoch-making were his studies of variable
stars in, and close to, globular clusters, in particular M53. Baade could prove - for the
first time - the existence of isolated stars in the halo, i.e. far outside the galactic
plane. He compared occurence and types of variable stars in fields with different
galactic latitudes, which later led to his famous discovery of the
two different stellar populations. Further work of Baade with the 1m Reflector
included, among others, the Orion nebula, and the discovery of two clusters of
galaxies in Ursa Maior. It is little known that Baade managed as early as 1921 (and
thus three years earlier than Hubble at Mt. Wilson) to identify three variable stars
in the nearby spiral galaxy M33 with the 1m Reflector.
Because these were not
Cepheids, they could not prove the extragalactic nature of M33. Baade never published
this discovery. Besides that, Baade regularly took up Schorr's favourite interest
and searched for comets and asteroids. His search resulted in the discovery of comet
1922II Baade, and the rediscovery of three periodic comets. In addition, several new
asteroids were found, among them the unusual object 944 Hidalgo which orbits the sun
far outside the asteroid belt, between Jupiter ad Saturn.
In 1931, Walter Baade left Hamburg Observatory to enter a new position at
Mt. Wilson Observatory (California). The twelve
years at his hands were the most productive phase in the history of the 1m Reflector.
Back in 1927, after he returned from his first visit to Anmerica, Baade had suggested
to move the telescope to a more southern region with better climate. This idea was
never realised, nor was Baades suggestion to convert the 1m Reflector into a Schmidt
During the following years, Richard Schorr took over the telescope again, using the
instrument once more for comet and asteroid observations. An exception was the
detailed investigation of the emission line spectrum of the Orion nebula by Rudolf
Minkowski, F. Goos, and P. Koch in the years 1931 to 1934. For that purpose, a prism
spectrograph with Fabry-Perot plate had been mounted in the telescope's prime focus.
Further observations, until 1939, were made by Brüggemann, Larink, Dieckvoß
Observational work rested during World War II, yet plans ripened to use the instrument
for stellar spectroscopy in the future. An already existing prism spectrograph,
originally bought for the Great Refractor, was intended to be used. However, it could
mounted in the prime or Newton focus. Moreover, a larger focal length was required -
usually realised in the Cassegrain or Coudé focus. In the middle of the war,
two new auxiliary mirrors were ordered from Zeiss: a hyperbolic convex mirror
to increase the focal length to 15m, and a flat mirror to direct the light beam out
of the tube towards the Nasmyth focus. Nobody intended to run the risk of drilling a hole
through the primary mirror as is usual for Cassegrain telescopes. In 1944,
the primary mirror was taken out, and sent to Jena for proper figuring of the new optics.
After the capitulation, its fate was uncertain, since Thuringia was first occupied by
America, but afterwards added to the Soviet occupation zone. That notwithstanding,
the mirror returned safely to Bergedorf about Christmas 1945, the auxiliary mirrors
following a little later.
The Zeiss spectrograph was put into service in autumn 1947.
This prism spectrograph has an unusual, very compact design with a folded
light path to avoid bending effects as far as possible. By exchange of
two prism boxes with one or three prisms in series, respectively, and with camera
objectives of different focal lengths, dispersions between 8 and 72 Å were
available. The light of an iron arc could be reflected into the light path to obtain
Between 1947 and 1972, thousands of star spectra were observed with this
instrument, among them the Zeta Aurigae systems, novae, radial velocity standards,
MKK standard stars, spectroscopic binaries, and variables. The most untiring
observers in these years were P. Wellmann and H.G. Groth. Other successful observers
with the 1m Reflector were, among others, D. Labs, J. Hardorp, T.
Herczeg, M. Grewing, I. Yavuz, U. Gehlich, and R. Wehmeyer.
In 1974 and 1975, a new grid spectrograph destined for the new
was tested at the 1m reflector. Between 1976 and 1978, finally, optical period
monitoring of the Crab pulsar, begun some years earlier at the
Great Refractor, was continued with the fast
photometer of the 1m Reflector. The old prism spectrograph was remounted in the
eighties, and the instrument was used only for teaching purposes (sun spectrum)
The 1m Reflector telescope is presumably the historically most valuable instrument at
Hamburg Observatory. On one hand, numerous exciting discoveries were made with the
instrument in he hands of one of the most important astronomers of the 20th century.
On the other hand , except for the change from Newton focus to Nasmyth focus, the
telescope is practically in its original state. Finally, it has a special rank in
technical history due to its nearly unique construction. Although the telescope is in
full working order, its general state is very poor. To avoid further damages, it
needs derusting and preserving. Unfortunately, neither the financial nor the
personal situation of Hamburg Observatory permits these works to be started.
German text and images: Matthias
Hünsch, historical fotos: Hamburg Observatory;
English translation: Kerstin Molthagen