Observatory building for seven inch heliometer, Cape, 1909.
© Science Museum / Science & Society Picture Library
Photograph of the observatory building for the seven inch aperture heliometer at the Cape Observatory, South Africa. Made by Repsold and Sons, Hamburg in Germany, the instrument has a split main lens that is used to measure very precisely the angular separation of objects in the heavens. Sir David Gill (1843-1914), Scottish astronomer, used this heliometer to determine stellar and solar parallax to measure the distance to nearby stars and that of the Sun.