Beer's fame derives from his hobby,
astronomy. He built a private
observatory with a 9.5 cm
refractor in
Tiergarten, Berlin. Together with
Johann Heinrich Mädler he produced the first exact map of the
Moon (entitled
Mappa Selenographica) in 1834–1836, and in 1837 published a description of the Moon (
Der Mond nach seinen kosmischen und individuellen Verhältnissen). Both remained the best descriptions of the Moon for many decades. In 1830, Beer and Mädler created the first globe of the planet
Mars. In 1840 they made a map of Mars and calculated its
rotation period to be 24 h 37 min 22.7 s, only 0.1 seconds different from the actual period as it is known today. ==Other work==