South Africa has been an important site for southern hemisphere astronomy since La Caille's observations in the 1750s. A new phase of international significance now dawns as the Square Kilometre Array (SKA) is being assembled in the Karoo. This huge project forms part of an international consortium and it promises to give South Africa a leading edge in radio astronomy. A strong developmentalist agenda pushed by its promoters goes along with the promise that science can benefit humankind. This article surveys the history of astronomy in South Africa from the perspective of the politics of knowledge. It identifies several different phases in the development of astronomy, from its colonial origins in the 19th century to its entrenchment as a South African-based discipline in the 20th century, following a long period of heavy reliance on investment and expertise from abroad. The article argues that astronomy was only fully 'nationalised' in the apartheid era. In the post-apartheid era, South Africa's special place as a portal into the southern skies has been important to the country's re-emergence as a site for the globalisation of knowledge and legitimated by the promise of a scientifically led 'African renaissance'. The article concludes by posing questions about the SKA's future in the light of the history of colonial and post-colonial knowledge exchange.