Johann Gottfried Galle

German astronomer

• Born: June 9, 1812; near Gräfenhainichen, Kingdom of Saxony (now Germany)
• Died: July 10, 1910; Potsdam, Germany

Nineteenth-century German astronomer Johann Gottfried Galle discovered several new comets and one of Saturn’s rings, but he is best remembered as the person who used another scientist’s calculations to find and view Neptune—the first planet to be discovered based on mathematical prediction.

Primary field: Astronomy

Specialties: Observational astronomy; theoretical astronomy; meteorology; astrophysics

Early Life

Johann Gottfried Galle was the eldest of seven children, born at the Pabsthaus (“Pope’s house”) near Wittenberg, Germany. His father operated a tar kiln business, dry-heating wood to derive pitch used in coating wooden ships to preserve them from rot. Johann received his primary education from a neighborhood pastor before he entered Wittenberg Gymnasium. After graduating in 1830, he hiked from Berlin to the Rhine River and Switzerland. He then enrolled at Berlin University.Among Galle’s teachers were many leading scholars, including the philosopher Georg Wilhelm Friedrich Hegel, astronomers Enno Dirksen, Christian Ideler, and Johann Encke, mathematician Johann Dirichlet, and physicists August Seebeck and Heinrich Dove. Galle graduated in three years and afterward taught mathematics for two years in high schools in Guben and Berlin.

In 1835, Galle was hired to assist his former astronomy professor, Johann Franz Encke (1791–1865), who had become the director at the newly built Berlin Observatory. Galle made regular meteorological observations and routinely studied various stars and planets while competing for telescope time with his superior, Encke, a veteran spotter of comets and asteroids who was a pioneer in calculating orbits of stellar objects.

Using the observatory’s telescope, which had an aperture of around nine inches, Galle in 1838 observed the so-called crepe ring (later called the C ring) of Saturn. Director Encke downplayed the discovery when presenting a paper to the Berlin Academy that year, instead promoting his own discovery, the Encke Gap, found in Saturn’s A ring, and the crepe ring remained unknown until its existence was published by the American astronomers William and George Bond in 1850.

Between December 1839 and March 1840, Galle found three comets—the first new comets found in five years—discoveries for which the young astronomer received the Lalande Prize from the French Academy of Sciences and specially struck medals from the king of Denmark.

Life’s Work

In 1846, after receiving his doctoral degree, Galle made the discovery for which he is best known: the planet Neptune. For his discovery—a major event, the first new planet to be found since the discovery of Uranus in 1781, and the last until the 1930 sighting of Pluto—Galle received the French Cross of the Legion of Honor and his second Lalande Prize. The following year, Galle was a major contributor to the Encke-edited second edition of Heinrich Wilhelm Olbers’s work, Abhandlungen über die Bahn eines Kometen (Papers concerning the courses of comets), providing a supplement that listed pertinent information about the 178 comets then known.

After sixteen years as an assistant in Berlin, and after publishing many scholarly papers in the German journal Astronomische Nachrichten (Astronomical news) Galle left in 1851 to become professor of astronomy and director of the observatory at the University of Breslau (today the University of Wroclaw, Poland). He remained there for the rest of his professional life.

In 1857, Galle married Cäcilie Eugenie Marie Regenbrecht (1827–86), daughter of the University of Breslau professor Michael Eduard Regenbrecht (1792–1849). Galle fathered two sons: Andreas, later a professor and longtime director of the Geodetic Institute in Potsdam, Germany, and Georg, later a physician in Hirschberg, Germany.

In 1872, Galle contributed a new technique of determining solar parallax, useful in ascertaining the value of an astronomical unit (AU), or the average distance between Earth and the sun, a fundamental measurement convenient for calculating the long distances and vast dimensions in space. Prior to Galle’s suggestion, the measurement of solar parallax was typically based on observations of a transit of the planet Venus across the disc of the sun, a relatively rare occurrence and fraught with difficulty due to the brightness of the sun and the uncertainty of its boundaries. Galle instead used celestial mechanics to observe against reference stars and to accurately calculate the distance to the minor planet Flora (discovered in 1847) in terms of AU. His method was afterward successfully employed to measure the distance of the near-Earth asteroid Eros (discovered in 1898) and to calculate the solar parallax with even greater accuracy.Galle retired from his posts at Breslau in 1897 and moved to Potsdam to be close to his elder son’s family and some of his grandchildren. Five years later, on the occasion of his ninetieth birthday, representatives from the Astrophysical Institute of Potsdam, the Berlin and Breslau Observatories, and other scientific organizations threw him a large celebration. He remained active, alert, and a faithful correspondent with his many friends in the scientific community until his death at age ninety-eight.

Impact

Galle was one of Germany’s most important nineteenth-century scientists. His telescopic discovery of Neptune using mathematical calculations thrust him into the limelight. The discovery launched further outward explorations, resulting in the sighting of the first Neptunian moon within weeks. Later observations of irregularities in Neptune’s orbit led to speculation that another unknown object might be causing the disturbances; the search culminated in the discovery of Pluto, considered the solar system’s ninth planet from 1930 to 2006, when it was downgraded to a dwarf planet.

In 1894, Galle made another long-lasting contribution to astronomy. With the assistance of his son Andreas (who had worked alongside his father in the observatory between 1880 and 1883 after graduating from the University of Breslau), he published a comprehensive catalogue of the 414 known comets and their attributes. The work, complete with names of objects and their discoverers, dates of observation, longitudes and latitudes of the comets, orbits and distances, classification by type and brightness, remained the definitive guide to comets for more than thirty years, when a plethora of new early-twentieth-century discoveries necessitated its updating.

For his many accomplishments during a long lifetime devoted to his science, a crater on the moon and a crater on Mars, an asteroid (2097 Galle), and one of Neptune’s rings were named in Galle’s honor.

Bibliography

Benton, Julius. Saturn and How to Observe It. New York: Springer, 2005. Print. Provides a wealth of data incorporating everything currently known about the solar system’s second-largest planet and its complex ring structure, plus a multitude of black-and-white and color photographs.

Galle, Johann Gottfried. Galle’s Catalogue of Comets, from 1860 to 1884: Translated from the Astronomische Nachrichten Nos. 2665 and 2666, by William C. Winlock and Reprinted from the Sidereal Messenger for November 1885, and January and February 1886. Charleston: Nabu, 2011. Print. A reprint of Galle’s comet charts, considered the most authoritative source of information on comets between the late nineteenth and early twentieth centuries.

Schilling, Govert. The Hunt for Planet X: New Worlds and the Fate of Pluto. New York: Springer, 2009. Print. A detailed account of the search for stellar objects, with a focus on the personalities, techniques, and controversies involved in the hunt. Includes interviews with scientists and many illustrations.

Standage, Tom. The Neptune File: A Story of Astronomical Rivalry and the Pioneers of Planet Hunting. New York: Berkley Trade Books, 2001. Print. Provides an account of the issues and characters behind the race to discover the planet that became known as Neptune, including reprints of actual documents related to the search.