Johann Heinrich Mädler (May 29 1794 – March 14 1874) was a German astronomer.

He was orphaned at age 19 by an outbreak of typhus, and found himself responsible for raising three younger sisters. He began giving academic lessons as a private tutor and in this way met Wilhelm Beer, a wealthy banker in 1824.

In 1829 Beer decided to set up a private observatory with a 95-mm refractor telescope made by Joseph von Fraunhofer, and Mädler worked there. In 1830 they began producing drawings of Mars which later became the first true maps of that planet. They were the first to choose what is today known as Sinus Meridiani as the prime meridian for Mars maps.

They made a preliminary determination for Mars' rotation period, which was off by almost 13 seconds. A later determination in 1837 was off by only 1.1 seconds.

They also produced the first exact map of the Moon, Mappa Selenographica, published in four volumes in 1834–1836. In 1837 a description of the Moon (Der Mond) was published. Both were the best descriptions of the Moon for many decades, not superseded until the map of Johann Friedrich Julius Schmidt in the 1870s. Beer and Mädler drew the firm conclusion that the features on the Moon do not change, and there is no atmosphere or water.

In 1836, Johann Franz Encke appointed Mädler an observer at the Berlin Observatory , and he observed with its 240-mm refractor. In 1840, Mädler was appointed director of the Dorpat Observatory in Tartu, Estonia, succeeding Friedrich Wilhelm Struve who had moved to Pulkovo Observatory. He carried out meteorological as well as astronomical observations. He continued Struve's observations of double stars. He remained in Tartu until he retired in 1865, and then returned to Germany.

By examining the proper motions of stars, he came up with his "Central Sun Hypothesis", according to which the center of the galaxy was located in the Pleiades star cluster and that the Sun revolves around it. He got the location wrong.

He published the two-volume History of Descriptive Astronomy in 1873.

Mädler crater on the Moon and Mädler crater on Mars are named after him.

External links

• http://www.uapress.arizona.edu/onlinebks/mars/chap04.htm

Obituary

• MNRAS 35 (1875) 171