Octagon Room, Flamsteed House at Royal Observatory, Greenwich, 2007 (photo)

The centrepiece of Christopher Wren's Flamsteed House was the Octagon Room, with tall windows and an elaborate plaster ceiling. One façade was orientated orientated north, though not exactly enough to allow certain types of observation, since another of the economies was building the Observatory on the pre-existing foundations of a demolished medieval tower, latterly called Greenwich Castle. The Octagon Room housed the original observatory and Flamsteed's eccentric collection of instruments, above the Astronomer Royal's own quarters. These were to be Flamsteed's home for nearly four decades. In this time he prepared some of the most accurate star maps ever produced, mainly using a transit telescope exactly mounted on the first 'Greenwich meridian' (north-south line) in a small brick shed at the bottom of the garden.