Alte Sternwarte, Observatory in Südstadt, Bonn, Germany.

Alte Sternwarte is a classical-style observatory at Poppelsdorfer Allee 47 in Bonn's Südstadt, built 1840–1844 to a design by Argelander and Peter Josef Leydel, revised in Berlin by Karl Friedrich Schinkel. The main building carries a central dome and six smaller cylindrical domes, two on each of its three side wings, giving the cross-shaped plan the IAU cites alongside Berlin's 1835 observatory. The separate Refraktorium of 1899 has a hemispherical dome.

The building was constructed between 1840 and 1844 following designs by architect Karl Friedrich Schinkel. It opened in 1845 and quickly gained status as a royal observatory, becoming one of the leading centers for astronomical observation.

Since 1975 the 1899 refractor room has been used by the Volkssternwarte Bonn, a public amateur observatory. The building's name lives on in the Argelander Institute for Astronomy, formed when the university's astronomical institutes merged in Endenich. Some original instruments are now in the University Museum Bonn and the Deutsches Museum in Munich.

The building is located on Poppelsdorfer Allee and is visible from outside, with parking available nearby. Visitors should check ahead about access, as it is not always open to the public and operates mainly for special events and guided tours.

The main building's domes are all cylindrical, but the detached 1899 Refraktorium has a hemispherical dome, the form more common in later observatories. Since 1975 the Volkssternwarte Bonn has used that refractor room. Some original instruments are now in the University Museum in Bonn and the Deutsches Museum in Munich.