The former astronomical observatory (IAU code 035) owned and operated by the University of Copenhagen. It opened in 1861 as a replacement for the University's old observatory at Rundetårn.

The foundation stone for the observatory at Rosenborg Bastion was laid on Nov. 15 1859 and it came into use in 1861. The building was designed by the architect Christian Hansen. Riflescope socket goes through the building and the hill down to the street level to avoid vibrations. Approximately 1/3 of the building bricks are used for the foundation. The garden in front of the observatory with the statue of Tycho Brahe was inaugurated in 1876. The original refractor-telescope was replaced with a bigger and better in 1895.