Johann Heinrich von Mädler (May 29, 1794- March 14, 1874) was a German astronomer. Along with his patron, Wilhelm Beer, he produced the first true maps of the planet Mars, and established the Sinus Meridiani as the prime meridian for Martian maps. They also came within 1.1 seconds of determining Mars' rotation period. They also produced the first accurate map of the Moon, Mappa Selenographica, published in four volumes between 1834 and 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 Both were the best descriptions of the Moon for many decades, not superseded until the map of Johann Friedrich Julius Schmidt in the 1870s. In 1836 Mädler was made an observer at the Berlin Observatory, and hev was appointed director of the Dorpat (Tartu) Observatory in Estonia in 1840. He remained in there until his retirement in 1865, and then returned to Germany. He published many scientific works, among them a two-volume History of Descriptive Astronomy in 1873.