The Archenhold Observatory, named in honor of Friedrich Simon Archenhold, is an observatory in Berlin-Treptow. It was opened to the public on 1 May 1896 as the Treptow Observatory to coincide with the Great Industrial Exposition of Berlin. Based on Archenhold's design it contained what was then the world's longest telescope, with a focal length of 21 m. The Observatory was named after Archenhold at its 50th anniversary in 1946.