Background

Johann Galle was born on June 9, 1812, in Radis, Germany. He was the son of J. Gottfried Galle and Henriette Pannier. He was born in an isolated house on the Dübener Heide, a wooded heath between the Elbe and the Mulde, where his father was manager of a tar distillery.

Education

Johann attended school at Radis, his mother’s birthplace. There the local clergyman prepared both one of his own sons and Galle for the secondary school at Wittenberg. Galle was at Wittenberg from April 1825 until April 1830, when he went to study in Berlin. His teachers there included Hegel, Dirichlet, Dirksen, Dove, Ideler, and Encke. In 1833 Galle was granted the facultas docendi to teach mathematics and physics at the Gymnasium level. Having continued his theoretical studies, Galle wished to obtain the doctorate. The government gave him financial aid and he received the degree on 1 March 1845. His thesis, Olai Roemeri triduum observationum astronomicarum, was based upon unanalyzed data from three days of exceptionally good meridian observations made by the Danish astronomer in 1706.

Career

Johann spent the required probationary year teaching at Guben and Berlin, where he was made assistant teacher at the Friedrich-Werder Gymnasium in March 1834. While he was teaching in secondary school, Galle kept in touch with Encke; and in 1835 Encke, who had become director of the Berlin Observatory, had Galle appointed to an assistantship that had been created especially for him.

Galle spent the next sixteen years at the observatory, where his duties concerned him largely with astrometry. He became in addition an avid observer of comets, including Halley’s comet in its appearance of 1835. In 1839 and 1840 Galle himself discovered, in quick succession, three new comets, and thus attracted the attention of experts in the field as well as royal recognition.

In 1836 Alexander von Humboldt invited Galle to participate in the computation of the astronomical material that he had collected during his journeys and thereby initiated a professional association that was to last fifteen years. During this same period, Galle again attended Encke’s lectures in order to further his theoretical knowledge, and Encke entrusted him with further computational work involving the minor planets, especially Pallas, which he had previously observed. In about 1839 Galle began to compute the ephemerides of this planet for the Berliner astronomisches Jahrbuch. He continued these calculations for thirty years. He made other computations of the elements and ephemerides of comets, including two of those that he had discovered. In 1838 he observed the crepe ring of Saturn, although he did not publish this discovery.

Le Verrier informed Galle of the presumed position of a planet beyond Uranus whose orbit he had computed from the perturbations of Uranus’ motion and encouraged Galle to look for this planet since he thought the telescopes available to him at the Paris observatory inadequate to this purpose. On 23 September 1846 he and d’Arrest, who was at that time studying in Berlin, searched the region cited and found it within 1° of the predicted position. The planet was at first called “Le Verrier’s planet,” but its name was shortly thereafter changed to Neptune.

Following the discovery of Neptune, Galle contributed observations and computations of a provisional circular orbit toward the further tracking of the planet. His modesty prevented him from capitalizing on his discovery, and it was Encke who reported in detail on it to the Berlin Academy and in the Astronomische Nachrichten. Galle’s achievement was nevertheless widely hailed.

Galle continued to work in Berlin as Encke’s assistant - he was even referred to as his teacher’s mirror image. Among other projects, Galle made numerous distance measurements of double stars and, in 1847, published a supplement to the new edition of Olbers’ Abhandlungen, a list of all comet orbits computed up to that time, with important emendations and references to the literature.

In June 1851 Boguslavsky died at Breslau and Galle was offered the post of director of the observatory and professor of the university there. It was not easy for him to decide to leave the well-equipped Berlin Observatory for a small, almost obsolete observatory situated in the very center of the provincial town, but he accepted the opportunity to do independent work. Galle stayed at Breslau for forty-six years. In 1856 he became Professor of Astronomy at the Schlesischen Friedrich-Wilhelms-Universität Breslau (today the University of Wrocław). In 1874-1875 he performed the duties of rector of the university. He taught all aspects of astronometry and meteorology, but devoted much of his classroom activity to studies of comets and planetoids. He was a vivid lecturer and attracted large audiences - as many as sixty auditors are recorded at one time.

The primitive equipment available at the Breslau observatory did not permit Galle to do any pioneer work. He did, however, often participate in astronomical-geodetical tasks for the Europäische Gradmessung. As late as 1885 and 1888, he took part in the determinations of longitude between Berlin and Breslau. He also continued to observe comets, although he was mainly concerned with meteors, a continuation of his work in Berlin. He had already found that there is a relationship between the meteor showers recorded over the centuries and the appearance of comets.

In 1864, Galle issued a new edition of Olbers’ Abhandlungen, this time including the orbits of 231 comets. In a supplement of 1885, he increased the number to 286.

As did many of his fellow astronomers, Galle made regular meteorological observations or had them made for him. As conditions for astronomical observations became worse at the Breslau observatory, he placed increasing emphasis on meteorological and even geomagnetic measurements. He conducted the latter from 1869 to 1897. These were considerably impaired, however, by the construction of a streetcar line near the university, started in 1893. Through these abortive observations Galle wished to examine the magnetism of the earth in relation to “northern lights and other terrestrial and even cosmic conditions.” He also published a series of papers on climatology and weather forecasting.

Achievements

• Johann Galle was an eminent astronomer who on September 23, 1846, was the first to observe the planet Neptune at the request of the French astronomer Le Verrier. He studied the rings of Saturn and suggested a method, later successful, of measuring the scale of the solar system by observing the parallax of asteroids. Throughout his life, Galle received numerous honors, especially memberships in scientific societies all over the world. Two craters, one on the Moon and one on Mars, the asteroid 2097 Galle, and a ring of Neptune have been named in his honor.

Works

More photos

• book

  • Galle's catalogue of comets from 1860 to 1884 1886
  • Verzeichniss der Elemente der Bisher Berechneten Cometenbahnen Nebst Anmerkungen und Literatur-Nachweisen 1894

Views

Galle tried to compute the orbit of the Lyrid meteor shower around the sun and to demonstrate its connection with comet 1861 I, discovered by Biela. He proved that meteors were to be expected to attend the descending node of the comet’s orbit. His theoretical assumptions were confirmed by a great number of shooting stars as predicted on the night of 28 November 1872, establishing the relation between meteor showers and the decomposition of a parent comet. Galle continued these investigations, examining a variety of significant meteor appearances and computing the Cosmic orbits of such meteors, which he classified as often hyperbolic.

Galle’s interest in the minor planets led him to propose in 1872 that corresponding data on these bodies, observed at a close approach to the earth, be used to determine the solar parallax. The oppositions of Mars and lower conjunctions of Venus, particularly its passages in front of the sun’s disk, had already been observed with this objective; but Galle, who was widely experienced in the observation of the larger planets, correctly stressed that observations of the planetoids should be free from systematic errors. Galle corresponded extensively with astronomers of leading observatories, particularly those in the southern hemisphere, on this proposal. His suggestions were adopted and a series of simultaneous observations of Flora were made. These showed close agreement with the values derived by Simon Newcomb from other measurements.

It is also known that Galle was also considering the possible existence of a planet between Mercury and the sun, a hypothesis repeatedly put forth by Le Verrier. He seems to have dismissed its likelihood, however, reasoning that such a planet of any notable magnitude would be visible during total solar eclipses or on other occasions.

Connections

In 1857 Galle married C. E. M. Regenbrecht, the daughter of a professor from Breslau. She died in 1887. They had two sons, one of whom, Andreas, was for many years an astronomer and geodesist at Potsdam.

Father:

J. Gottfried Galle

Mother:

Henriette Pannier

Spouse:

C. E. M. Regenbrecht

Son:

Andreas Galle

colleague:

Johann Franz Encke

References

• Dictionary of Scientific Biography