Lilienthal observatory

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The Lilienthal observatory

The Lilienthal observatory was an astronomical research facility founded in 1782 by Johann Hieronymus Schroeter in the village of Lilienthal near Bremen . It was largely destroyed in the Napoleonic Wars in 1813. With its instrumentation - especially large reflector telescopes - it was one of the world's leading observatories at the beginning of the 19th century .

history

In 1782, the chief bailiff Johann Hieronymus Schroeter , who was interested in astronomy , was transferred to Lilienthal in the service of the Electorate of Braunschweig-Lüneburg . He first set up a simple observation station in the garden of the office building.

Schroeter was acquainted with the Herschel family from Hanover and was in correspondence with Wilhelm Herschel , who lived in England and who had discovered the planet Uranus in 1781 . In 1784, Schroeter received a mirror with a diameter of 12 cm and eyepieces from Herschel, from which he made a mirror telescope . In 1786 Herschel sent him a mirror with a diameter of 16.5 cm, which he used for another telescope. In the same year Schroeter had a two-story observatory built in the official garden. A terrace led out of the basement onto which telescopes could be pushed. The upper floor was provided with sliding roof flaps.

In 1788, a second observation station was built about 70 meters away, an octagonal wooden structure that he called the "Urania Temple". From 1792 he developed with Professor Johann Gottlieb Friedrich Schrader from the University of Kiel and his gardener Harm Gefken methods for optimizing metallic telescopic mirrors. Devices with very good imaging performance were created, such as a telescope with a 24 cm aperture. In 1793 he began to manufacture a " giant telescope ", which was completed in 1794. It had an aperture of 50.8 cm and 8.25 m (27 feet) focal length . This telescope made the Lilienthal observatory world famous and from then on it was visited by astronomers, high state officials and the military from all armies.

Together with Franz Xaver von Zach and Heinrich Wilhelm Olbers , Schröter founded the Astronomical Society in Lilienthal in 1800 .

From 1799 onwards, Schroeter's salary as a senior bailiff was no longer sufficient to maintain the observatory and the costs of his publications. He therefore concluded a contract with the British-Hanoverian King George III through the mediation of a London friend . from. After that, all of the equipment in the observatory became the property of the king for the price of 1,200 English guineas (around 150,000 euros based on today's value). The devices were to remain in Lilienthal until Schroeter's death and then go to the University of Göttingen . Schroeter also received a pension of 300 thalers as well as 200 thalers for the maintenance of an "observatory inspector".

Karl Ludwig Harding , who had been teaching Schroeter's son Johann Friedrich since 1796, became the inspector . Harding discovered the third asteroid Juno from Lilienthal in 1804 . In 1805 he went to the University of Göttingen.

From 1806 to 1809 Friedrich Wilhelm Bessel worked as an assistant in Lilienthal. In 1809 Bessel received a call to the University of Königsberg .

Schroeter's former gardener Harm Gefken used his acquired knowledge and founded an optical workshop in Lilienthal for the manufacture of reflector telescopes, where he also supplied Schroeter. In the course of time, important work was done in Lilienthal on the moon and the planets Mercury , Venus , Mars , Jupiter and Saturn . This is also where Schroeter's large lunar atlas “Selenotopographical Fragments” was created.

As a result of the Napoleonic Wars , Lilienthal came under French administration in 1810 and Schroeter was forced into retirement. His salaries were no longer paid, the money from England had not been paid since 1806. On April 21, 1813, French troops carried out a punitive expedition and burned the village of Lilienthal. Schroeter's office house and records burned. The observatory was spared, but was looted. In November 1813, Schroeter was reinstated in his office. As his health deteriorated, he contracted to have all instruments that had been bought before 1799 transported to Göttingen. In 1816 Schroeter died in Lilienthal at the age of 70. After his death, the observatory deteriorated increasingly. In 1850 the last remains were torn down.

Today there is a local museum in Lilienthal , where some of the original telescopes can be viewed. A model of the giant telescope is located on an outer surface.

Furnishing

The first device at the observatory was an achromat from Dollond with a 5 cm aperture, 91.5 cm focal length and five interchangeable eyepieces, which Schroeter had purchased in 1799. He later set up the device in the "Urania Temple". A French officer stole the telescope during the looting in 1813. Schroeter received it again later.

The first reflector telescope from 1784 made of parts by Wilhelm Herschel had an aperture of 12 cm and a focal length of 122 cm. Eight eyepieces enabled 60 to 339 times magnifications .

The second reflecting telescope with a Herschel mirror had a 16.5 cm aperture and 2.14 m (7 feet) focal length. Ten eyepieces provided magnifications from 74 to 1200 times. The components cost 600 Reichstaler , which at the time was almost half of Schroeter's annual salary.

From 1792 onwards, several telescopes were manufactured in-house. Two of them, one with a 16.5 cm aperture and 2.14 m focal length (according to Schroeter's statements, absolutely equivalent to the Herschel devices), and one with a 24 cm aperture and 3.96 m (13 feet) focal length, remained in Lilienthal. The latter had excellent imaging performance and was the best telescope in the observatory for several years.

He obtained a micrometer glass from Augsburg optician Höschel , which he had made based on a model by Schroeter. This divided the field of view into parallel lines between 4 and 26 arc seconds . The device made it possible to determine the angular distances between stars.

Replica of Schroeter's telescope from 1794 in Lilienthal

The famous 27-foot “Lilienthal Giant Telescope” had an aperture of 50.8 cm and a focal length of 8.25 m. The metal mirror had been cast and polished by Schroeter and Gefken. It was 6 cm thick and weighed about 100 kg. To improve the reflectivity , 5 kg of arsenic were also processed. The tube was octagonal and made of fir wood. The entire telescope weighed around 700 kg. It was attached to a two-story 3.5 m wide and 6.5 m high brick tower with oak timber framework . The incline was aligned using pulley blocks , the horizontal movement via a bogie. The “gallery” (an observation area for several people) was moved around the telescope within a radius of 10.5 m. The telescope had two smaller finderscopes. Schroeter had special eyepieces made for his giant telescope, which allowed a magnification of 179 to 360 times. Schroeter estimated the total weight of the system at 20 tons.

In order to make comparisons with his own telescopes, Schroeter acquired the largest refractor of the time with a lens of 10 cm diameter and 3 m focal length from Dollond in 1795 . It was set up in the "Urania Temple" and later equipped with an equatorial mount . Schröter was satisfied with the device, but mostly observed with his own more powerful telescopes.

In 1803 Schroeter acquired a reflector telescope with a focal length of 2.14 m from Gefken's workshop.

Another device from its manufacture followed in 1805. It had an aperture of 30.5 cm and 5.57 m focal length. Gefken had re-ground a mirror made in 1796 that was intended for a 20-foot telescope. However, the device had proven unwieldy and was not used. The telescope built by Gefken was considered a masterpiece and, according to Schroeter, allowed 2000x magnifications.

In 1806 Schröter acquired two achromatic lenses with a focal length of 91 cm and 3.69 m from the "Optical Institute" founded by Fraunhofer in Benediktbeuern . However, the devices did not meet his expectations.

In 1807 another large, free-moving telescope was built in the official garden. The mirror manufactured by Gefken had a diameter of 30.5 cm with a focal length of 6.1 m. The telescope was attached to a scaffolding that ran on a rail circle of 12 m. The construction could be operated by one person.

Others

The writer Arno Schmidt (1914–1979) planned a novel about the Lilienthaler Astronomen-Kreis, but it never came about. Schmidt processed some of the collected material in his 1960 novel KAFF also Mare Crisium , which plays both in a " dump " on the edge of the Lüneburg Heath and on the moon and there in the area of ​​the lunar sea, Mare Crisium . Schmidt's remaining drafts of a Lilienthal novel were published from the estate in 1996.

literature

Web links

Individual evidence

  1. ↑ Fragments for a precise knowledge of the lunar area . On: website of the Deutsches Museum ; Retrieved November 2, 2013.

Coordinates: 53 ° 8 ′ 28.2 "  N , 8 ° 54 ′ 45.5"  E