Johann Heinrich von Madler (May 29, 1794 - March 14, 1874) was a German astronomer. He gave 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, and Madler 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 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. In 1836, Johann Franz Encke appointed Madler an observer at the Berlin Observatory. In 1840, he was appointed director of the Dorpat (Tartu) Observatory in Estonia where he made meteorological as well as astronomical observations. He remained in Tartu until he retired in 1865, and then returned to Germany. Next to his other numerous and important works, he made calculations concerning the true length of the tropical year with precision never attained before, though this fact is little known. He died in 1874 at the age of 79.