The National Maritime Museum represents an ensemble of important historic buildings set within an iconic landscape, the whole comprising theGreenwich World Heritage Site. The project for the Royal Observatory inGreenwich Park encompasses the restoration and upgrading of the SouthBuilding, a new planetarium and the redesign of the landscaping andvisitor route through the museum. This exciting new development respondsto the diverse demands of planetarium audiences, education groups andsite visitors whilst opening up the south half of the Royal Observatory site.A new 118 seat planetarium has been inserted in the centre of the site.Access to the auditorium is at lower ground level through a spacious newfoyer. The Peter Harrison Planetarium is housed in a cone whose geometryreflects key astronomical concepts in its relation to the space. Above roundthis is manifested as a tilted bronze cone aligned with the north star at51.5°. The disc cut at 90° through its apex is parallel to the celestialequator. This plane is clad in layers of reflecting glass in which the spaceof the passing sky is revealed.The cone is constructed from 250mm concrete to keep out sound, whichis clad in an 8mm thick phosphor bronze carapace. The metalwork wasprefabricated in Gateshead then brought to site in 18 segments, whereit was site welded to achieve the exact conic geometry of an astronomicalinstrument. The final bronze finish has been achieved by layers ofpatination, a technique usually applied to bronze sculptures, which willget richer over time.