Christie's altazimuth in dome, Greenwich, London, 1914.
© Science Museum / Science & Society Picture Library
Photograph showing Christie's Altazimuth installed at the Royal Observatory, Greenwich in 1896. Designed by the Astronomer Royal, W H Christie (1845-1910) the instrument was used make observations anywhere in the sky. Unlike a transit instrument, which is limited to measuring an object's position in the north-south meridian, the altazimuth could make measurements in any direction. This was particularly important for monitoring the complex motion of the Moon and allowed observations to be made at every opportunity. The instrument is shown with the telescope lifted off the trunnions, so that its pivots can be reversed. Today the observatory now forms part of the National Maritime Museum. The dome for this instrument is now occupied with a telescope used for public viewing.