Johann Hieronymus Schröter

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Johann Hieronymus Schröter (August 30, 1745 – August 29, 1816) was a German astronomer.

Schröter was born in Erfurt, and studied law at Göttingen University from 1762 until 1767, after which he started a ten-year-long legal practice.

In 1777 he was appointed Secretary of the Royal Chamber of George III in Hanover, where he made the acquaintance of two of William Herschel's brothers. In 1779 he acquired a three-foot-long (91 cm, almost one metre) achromatic refractor with 2.25 inch lens (50 mm) to observe the Sun, Moon, and Venus. Herschel's discovery of Uranus in 1781 inspired Schröter to pursue astronomy more seriously, and he resigned his post and became chief magistrate and district governor of Lilienthal.

In 1784 he paid 31 Reichsthaler (about 600 Euros) for a Herschel reflector of 122 cm focal length and 12 cm aperture. He quickly gained a good name from his observational reports in journals, but was not satisfied and in 1786 paid 600 Reichstaler (an equivalent of six months earnings) for a 214 cm focal length 16.5 cm aperture reflector with eyepieces allowing up to 1,200 magnification, and 26 Thaler for a screw-micrometer. With this he systematically observed Venus, Mars, Jupiter, and Saturn.

Title page from the Selenetopographische Fragmente

Samples from moon maps in the Selenetopographische Fragmente

He made extensive drawings of the features of Mars, yet curiously he was always erroneously convinced that what he was seeing was mere cloud formations rather than geographical features. In 1791 he published an important early study on the topography of the Moon entitled Selenotopographische Fragmente zur genauern Kenntniss der Mondfläche. In 1793 he was the first to notice the phase anomaly of Venus, now known as the Schröter effect, where the phase appears more concave than geometry predicts.

In his later years he suffered the disruptions of the Napoleonic Wars when his observatory was looted by French troops.

His drawings of Mars were not rediscovered until 1873 (by François J. Terby) and were not published until 1881 (by H. G. van de Sande Bakhuyzen), well after his death.

Schröter crater on the Moon and Schroeter crater on Mars are named after him. Also, Vallis Schröteri (Schröter's Valley) on the Moon is named after him.

[edit] References

William Sheehan & Richard Baum, Observation and inference: Johann Hieronymous Schroeter, 1745–1816, JBAA 105 (1995), 171 [1]
Mallama, A. (1996). "Schroeter's Effect and the twilight model for Venus". Journal of the British Astronomical Association 106 (1): 16–18.