The astronomy collection - Observatoire astronomique de Strasbourg

The Strasbourg Observatory’s collection includes more than 200 instruments: its quality and diversity reflect the complexity of its long history.
It includes in particular :

fixed objects such as equatorial telescopes, meridian circles and the Repsold altazimut
objects for representing celestial bodies, including Coronelli’s celestial globe, an armillary sphere by Delamarche and an original moon globe by von Lade
movable instruments such as chronoscopes, sextants…

TO BE DISCOVERED DURING THE VISIT

Coronelli’s celestial globe
The comet finder
The large refracting telescope
The altazimuth
The Newton telescope
The clocks

OTHER REMARKABLE PIECES OF THE COLLECTION

The meridian circle
The Cauchoix meridian telescope
The Moroccan astrolabe
The Western astrolabe
The Humboldt instruments

TO BE DISCOVERED DURING THE VISIT

Coronelli’s celestial globe

The comet finder

The Merz-Repsold comet finder consists of a refractor with a diameter of 162 millimetres and an azimuthal chair in which the observer could sit. This azimuthal mount allows the sky to be scanned along parallels to the horizon, which increases the chances of discovery. The comet finder’s observation chair pivots on a wooden axis and is equipped with a system that allows it to be tilted. The armrests are equipped with levers that allow for movement in azimuth and height. The whole unit was mobile, as it was positioned on rails around the Grande Coupole.

The large refracting telescope

The Merz-Respold equatorial refracting telescope was built for the Imperial Observatory in Strasbourg in 1879 and installed in 1881. It was the most powerful refracting telescope in Germany.
The objective of the telescope has an aperture of 49 cm and a focal length of 7 metres. It is the third largest refracting telescope in France after those in Paris-Meudon and Nice.
The telescope was dismantled by German astronomers at the beginning of the First World War to protect it from possible bombing. After the observatory was handed over to France in 1918, Ernest Esclangon, the then director of the observatory, undertook to refurbish and electrify the dome and the instruments. It was not until 1922 that the lens was replaced in its barrel. The mobile staircase is the originality of this dome: it allows the observer to follow the rotation movements of the telescope without having to turn his eye away from the eyepiece.

View of the upper part of the instrument

The altazimuth

The altazimuth was built in Hamburg in 1879 by Repsold. When the observatory was founded, it was installed in the northern dome of the meridian observation building. This instrument, one of the largest of its kind, was used to replace the meridian circle in bad weather. It could fulfil the functions of the first vertical and was also used for the measurement of declinations of circumpolar stars by observing their greatest elongations, for measuring latitude with the Talcott method, for the observation of the moon or as a universal instrument. It can also be used for daytime observations.
Despite its versatility, it seems that the use of this instrument was quickly abandoned. Indeed, it presents some imperfections at the level of its mount which makes it an instrument lacking in precision.

View of the restored and reassembled altazimuth

The Newton telescope with Herschel suspension mount

There is very little evidence to situate this Newton telescope historically. The instrument is not signed, and the optical part and the mirror are missing. It may be a local construction based on the Herschel system. It has an octagonal tube made of oak and a suspension mount, also made of oak. The mount is placed on a wooden frame with three castors.

THE CLOCKS

Astronomical clock (Riefler constant pressure astronomical controller No 95)

This Riefler Astronomical Constant Pressure Regulator has a circular silver brass dial with a gold brass frame. The large dial shows the minutes, the small upper dial the seconds and the small lower dial the hours.

Horloge astronomique (régulateur astronomique Petit No 340)

This regulator comes from the old Observatory which was located in the rue de l’Académie, and seems to date from 1840. At that time, German astronomers used the Cauchoix telescope to observe the Moon and planets and to determine the time.
This is a rare example of a regulator with sidereal and mean time.

Astronomical clock (Schweizer astronomical regulator No. 58)

This clock is probably the first precision clock installed at the Strasbourg Observatory; it was acquired at the same time as a second identical clock. One of these two clocks was installed in the Grande Coupole.

Riefler Astronomical Controller No. 95, front view

OTHER REMARKABLE PIECES OF THE COLLECTION

The meridian circle

Old view of the observation room
of the Repsold meridian circle

The Repsold meridian circle, built in 1880, is installed in the meridian room of the observation building. The room has a through opening, a zenith hatch and high windows to allow the meridian axis to be seen for observations. The meridian circle was originally equipped with two sights for the control of the rotation axis and two sights for collimation. The huts housing the north and south sights are still visible in the observatory garden.
The meridian circle is still in its original location today, the room having been converted into a working area.

The Cauchoix meridian telescope

This refracting telescope was made for the observatory located in the rue de l’Académie around 1840. Its use is only documented from 1872. It was installed on a vault of the building and used to determine the time, observe the Moon and the planets. Once installed in the new Observatory located on the imperial campus, the Cauchoix telescope was used for student instruction. The instrument was then installed in the western meridian room, the current planetarium.

The Moroccan astrolabe

The Moroccan astrolabe has five Arabic tympans, two astrological tympans as well as an eighth tympan, added later, for the latitude of 48° – the instrument probably passed into Western hands in Strasbourg.

This astrolabe bears the inscription in kufic Arabic Made by Abû Bakr ibn Yûsuf in the city of Marrakesh – may God make it prosperous – in the year 605 [605 A.H. or 1208/9]. Little is known about this astrolabe maker except that he was one of the greatest instrument makers of the Maghreb in his time. Six pieces of his production have been identified.
This instrument, which was part of the collection of Julius Reichelt (1637-1719), creator of the observatory in the Tower of the Hospital in Strasbourg in 1673, was given to the university by his son-in-law, Johann Joachim Haubenstricker, in 1719. It fell into oblivion before being rediscovered by chance by Pierre-Frédéric Sarrus (1798-1861), professor of mathematics at the Strasbourg Faculty of Science, in 1830, while clearing the old observatory of the civil hospital. Sarrus spent several years studying the astrolabe before publishing a detailed description in 1852.

For more information : https://oscahr.unistra.fr

The Western astrolabe

The second astrolabe was made in 1579 by Johannes Krabbe (1553-1616). It is the first astrolabe made by the German silversmith – he was only 26 years old at the time. We know that he made a second one in 1583, as well as others, made of paper or cardboard, which have not survived. The young craftsman, whose practical intelligence was complemented by solid scientific knowledge, tried to make the astrolabe accessible to everyone through his work: he was the first to recommend the manufacture of paper astrolabes to be glued to wood or cardboard. He also published a treatise, Newes Astrolabium, in 1609 in Frankfurt am Main, which accompanied the use of the astrolabe. The work was written not in Latin, the scholarly language of the time, but in German, in order to make it accessible to all those likely to use the compass and the square: doctors, astronomers, soldiers, surveyors, stonemasons, architects and sailors. The success of this manual was demonstrated by its six editions.

For more information : https://oscahr.unistra.fr

The Humboldt instruments

Among the 75 instruments used by the famous German naturalist Alexander de Humboldt (1769-1859), 9 came to the Strasbourg Observatory at the end of the 19th century. Four of them remain today: two sextants, an astronomical telescope and a black mirror.
The sextant is used to measure the height of a star above the horizon and has a graduated sector with an opening of 60°, which gave it its name. The two Humboldt sextants held by the observatory were built at the beginning of the 19th century by the best English manufacturers of precision instruments, one by Jesse Ramsden (1735-1800) and the other by Edward Troughton (1753-1830). The latter instrument is accompanied by a black mirror, an accessory that serves as an artificial horizon to take the height of the Sun by reflection. Listed in the inventory of the Strasbourg observatory’s equipment since 1872, alongside an astronomical telescope by Dollond (1731-1821), the three instruments were used by Humboldt during his various scientific expeditions: Troughton’s sextant was taken by Humboldt when he travelled to Asia in 1829, at the invitation of Tsar Nicholas I, to search for minerals in Asian Russia. Ramsden’s sextant was part of Humboldt’s 1799-1804 voyage to America with the French botanist Aimé Bonpland (1779-1858). Although the trajectory of these objects remains mysterious, their presence in Strasbourg attests to their highly symbolic value.