Johann Hieronymus Schroeter

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Johann Hieronymus Schroeter

Johann Hieronymus Schroeter (partly also Schröter ; born August 30, 1745 in Erfurt , † August 29, 1816 in Lilienthal ) was a leading German astronomer and administrative officer . He carried out the most precise observations of the planets , made very detailed moon maps and built large mirror telescopes . The Lilienthal observatory he built was equipped with the largest telescopes in Europe and was the place where Friedrich Wilhelm Bessel began to work in astronomy.

Life

Youth and student days

Johann Hieronymus Schroeter was born the son of a lawyer. The father died when Schroeter was nine years old. After completing his school education, he began studying theology at the University of Erfurt in 1762 . He was also interested in music and astronomy . A makeshift observatory with a telescope had been set up in the tower of the Schottenkirche . Here he was observing the sky with friends.

In March 1764 changed Schroeter at the University of Göttingen to law study. He also heard physics and astronomy from Abraham Gotthelf Kästner , who became his patron, and regularly visited the Göttingen observatory. In 1767 he completed his law studies and began a career as a civil servant - first in Polle an der Oberweser, then in Herzberg am Harz .

From lawyer to astronomer

In 1777 Schroeter was transferred to Hanover as secretary of the “Royal Chamber” . Through his interest in music, he got to know the family of the Hautboist and mechanic Isaak Herschel . His second son, Wilhelm Herschel , had gone to England as a musician and was now working as an astronomer with self-made telescopes .

Inspired by the reports of Herschel's siblings, Schroeter turned again to astronomy. He first borrowed a simple telescope from an optician . After advice and mediation from Dietrich Herschel, in 1779 he acquired a double- lens (pure color) terrestrial telescope, an achromatic lens from John Dollond with a 2¼ inch aperture and 3 feet focal length (approx. 5½: 91 cm) with 5 interchangeable eyepieces (22 to 130 times) . He began by observing the sun , moon and planets . Wilhelm Herschel's discovery of Uranus in 1781 prompted Schroeter to conduct systematic and more intensive observations of the sky.

In May 1782 Schroeter was transferred to the secluded moorland village of Lilienthal near Bremen , where he took up a position as senior bailiff. This activity gave him enough time to devote himself to astronomy. In the garden of the office building he first set up a simple observatory. In 1784 he built a powerful reflector telescope with a 12 cm aperture and 122 cm focal length. Wilhelm Herschel had sent him the mirror and eight eyepieces from England. Schroeter published the results of the observations of the moon and Venus made with it in specialist publications.

Private observatory, giant telescope and "Sky Police"

After an intensive exchange of letters with Herschel, Schroeter received additional components in 1786 with which he built a reflector telescope with a 16.5 cm aperture and 2.14 m focal length. He had a two-story observatory built in the garden. He wrote work plans for the systematic investigation of the sun, moon, Venus, Mars , Jupiter , Saturn as well as variables , double stars and foggy objects .

In 1788 Schroeter set up a second observation site in the garden, which he named "Urania Temple". In his observations he benefited from his excellent visual acuity . He was therefore particularly critical of his self-made telescopes and continued to improve their performance.

Replica of Schroeter's telescope from 1794 in Lilienthal (completed in 2015)

In 1792 he made the acquaintance of Professor Johann Gottlieb Friedrich Schrader from the University of Kiel . In the period that followed, the two of them, together with Schroeter's gardener Harm Gefken, optimized the process for manufacturing telescope mirrors, which at that time were still made of metal . To increase the reflectivity , they vaporized a layer of arsenic on the conventional copper - tin alloy. After appropriate adjustment, telescopes with very good imaging performance were created, e.g. B. one with 24 cm opening.

In 1794 he completed a " giant telescope " with a 50.8 cm aperture and 8.25 m focal length. It was mainly used to observe the night side of the moon, the registration of nebulae and star clusters and the planets in daylight. It was through the telescope that Schroeter became famous and he received visits from astronomers, high-ranking officials and the military.

With Franz Xaver von Zach and Heinrich Wilhelm Olbers , he founded the Astronomical Society in Lilienthal in 1800 to promote the dissemination of knowledge and discovery data. Schroeter became the first president of the society. He and Zach organized the so-called " Sky Police " for a targeted search for a suspected planet between the orbits of Mars and Jupiter (see Titius-Bode series ). The areas around the ecliptic were assigned to different observatories and the search was started, but by chance Piazzi discovered the first minor planet (1) Ceres in Palermo . In contrast, the asteroids (2) Pallas , (3) Juno and (4) Vesta were discovered in Bremen and Lilienthal in the following years .

Harding and Bessel

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 sold the entire equipment to the Anglo-Hanoverian King George III. The devices remained in Lilienthal. Schroeter received 1200 English guineas (according to today's value about 150,000 euros ), a pension of 300 thalers and 200 thalers for the maintenance of an "observatory inspector". After Schroeter's death, the devices were to go to the University of Göttingen.

Schroeter employed two inspectors one after the other who, as a result of their achievements in Lilienthal, received important positions in astronomy. The first inspector was the studied theologian Karl Ludwig Harding , who had been teaching Schroeter's son Johann Friedrich since 1796. Harding discovered the third asteroid Juno in Lilienthal in 1804 ; In 1805 he went to Göttingen University as a professor. His successor was the trained businessman Friedrich Wilhelm Bessel , who worked as an assistant in Lilienthal from 1806 to 1810. In 1809 he was appointed to the University of Königsberg , where he carried out pioneering work over the next few decades.

Schroeter's former gardener Harm Gefken used his acquired knowledge and founded an optical workshop in Lilienthal for the manufacture of reflector telescopes, which he also supplied to Schroeter. Gefken died in 1811 at the age of 55.

The end of the observatory

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 and his records were also burned. The observatory was spared, but was looted. In November 1813, Schroeter was reinstated in his office. However, as his health deteriorated, he had all instruments that had been bought before 1799 transported to Göttingen in accordance with the contract .

On August 29, 1816, the day he completed his 71st year of life, Schroeter died in Lilienthal. He was buried on the west side of the monastery church there.

After his death, the observatory fell into disrepair. The last remains were demolished in 1850.

Scientific work

Title page of the selenotopographical fragments
Moon maps in selenotopographical fragments

In 1791 Schroeter published the first part of his extensive work on the moon, the Selenotopographical Fragments, at his own expense . They contained 43 panels with images of the lunar surface, which had been created in countless nights of observation. For his drawings, Schroeter used a map of the moon by Tobias Mayer , who first divided the moon into degrees of longitude and latitude .

In 1796 Schroeter published a work on Venus, the Aphroditographic Fragments . He had found that there were systematic differences between the geometrically calculated phase of Venus and the phase actually observed. First of all, Schroeter said that these irregularities, as in the case of the Earth's moon, are due to surface details, e.g. B. mountain ranges, declined. In a paper published in 1803 on the Venus phase at the time of the dichotomy (half-venus), he correctly concluded that it was twilight effects in the Venusian atmosphere. This is why this phenomenon is now generally called the “Schroeter effect” after the name introduced by Patrick Moore . The effect can easily be observed as "Venus horns" even with small telescopes.

In 1800 the Hermographic Fragments about the planet Mercury appeared , in 1802 the second part of the moon work.

In 1808 he summarized his observations of the planet Saturn and its satellites in the Kronographic Fragment (n) .

In 1802, Schroeter determined that the fixed stars closest to the sun were so far away that their annual parallax must be less than 0.75 arc seconds . This was confirmed in later investigations: His former assistant Friedrich Wilhelm Bessel was able to measure a star parallax ( 61 Cygni ) with 0.3 "in 1838 .

Schroeter's 1803 areographic contributions to a more precise knowledge of the planet Mars initially remained unpublished. It was not until 1881 that the Leiden University , which held the records, had them printed. The work caused a stir in specialist circles. Schroeter had already described the phenomenon of the Martian canals in it, but viewed them as optical illusions .

Schroeters instruments

In addition to his excellent visual acuity, the constant improvement of his instruments also played a major role in Schroeter's success. The arsenic-coated mirrors developed jointly with Schrader and Gefken were optically equivalent to those by Herschel, but only cost half as much. However, the brittle material had to cool down very slowly. The best pieces, which with 6½ and 9½ inch aperture corresponded to today's standard of the "eight-inch", kept Schroeter as the so-called "Schrader" for his observatory himself. The larger "13-foot" mirror with a focal length of 4 meters provided unusually sharp Images and was considered the best Lilienthal telescope for many years. With it, Schroeter was able to go to the optical limits when observing planets and the moon, and with special eyepieces magnified up to 500 times.

The telescopes received a device that allowed the free opening to be gradually reduced to 3 inches, thereby completely eliminating the so-called "irradiation", a glare that otherwise required corrections in the calculations when determining planetary diameters. They also received eyepiece mounts with a uniform diameter. This enabled the respective eyepiece to be used on several instruments to control observation results and the number of possible magnification scales increased.

Memberships

Johann Hieronymus Schroeter was a member (full or corresponding) of the following scientific societies:

Posthumous honors and commemorations

In Lilienthal today there is a home office where a model of the observatory can be viewed.

The lunar crater Schröter , the moon valley Vallis Schröter , the Martian crater Schroeter and the asteroids (4983) Schroeteria and (28547) Johannesschröter were named after Schroeter .

In his hometown Erfurt a street bears his name.

Others

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

literature

  • Johann Hieronymus Schroeters Mondatlas 1791, The 43 copper plates from the "Selenotopographical Fragments" facsimile true to the original, provided with explanations, Albireo Verlag, Cologne 2018, ISBN 978-3-9816040-5-4 .
  • Günther Oestmann:  Schroeter, Johann Hieronymus. In: New German Biography (NDB). Volume 23, Duncker & Humblot, Berlin 2007, ISBN 978-3-428-11204-3 , p. 590 f. ( Digitized version ).
  • Harald Kühn: Johann Hieronymus Schroeter. Family history news. In: Heimat-Rundblick. History, culture, nature . No. 98, 3/2011 ( autumn 2011 ). Druckerpresse-Verlag , ISSN  2191-4257 , pp. 28-29.
  • Peter Richter, Harald Kühn (author); Heimatverein Lilienthal e. V. (Ed.): Fascinated by the world of stars. The Lilienthal astronomer Johann Hieronymus Schroeter and his unusual family history discovered 200 years later. New edition. Druckpresse-Verlag, Lilienthal 2013, ISBN 978-3-9815264-2-4 .
  • Jörg Drews / Heinrich Schwier (eds.): "Lilienthal or the astronomers". Historical materials for a project by Arno Schmidt . edition text + kritik, Munich 1984, ISBN 978-3883771694 .
  • Dieter Gerdes, (author); Heimatverein Lilienthal e. V (Ed.): Die Lilienthaler Sternwarte 1781 to 1818, Publisher : Simmering, M, Lilienthal (1991), ISBN 978-3927723092

Web links

Commons : Johann Hieronymus Schroeter  - Album with pictures, videos and audio files

Individual evidence

  1. ^ Gazetteer of Planetary Nomenclature
  2. ↑ Susanne Fischer (Ed.): Arno Schmidts Lilienthal 1801, or Die Astronomen . 19 four-color facsimiles with transcriptions, illustrations and photos. Suhrkamp Verlag, Frankfurt 1996, ISBN 978-3518800737 .


personal data
SURNAME Schroeter, Johann Hieronymus
ALTERNATIVE NAMES Schröter, Johann Hieronymus
BRIEF DESCRIPTION German lawyer and astronomer
DATE OF BIRTH August 30, 1745
PLACE OF BIRTH Erfurt
DATE OF DEATH August 29, 1816
Place of death Lilienthal