Year-going clock by Thomas Tompion, 1676

This is one of two clocks especially commissioned by Sir Jonas Moore, Master of Ordnance and patron to the first Astronomer Royal, John Flamsteed, for use at the Royal Observatory from its opening in 1676. The weight-driven clock was originally fitted with a 13 foot pendulum that was suspended behind the wainscot in the north-eastern corner of the Great Room.

The clock offered unprecedented accuracy and allowed Flamsteed to determine that the speed of the Earth’s rotation was constant. This proof was fundamental to the work at the Observatory in providing an accurate method of determining Longitude at sea.

Following Flamsteed’s death in 1719, the clock was sold by his Widow, Margaret and was subsequently converted for use as a domestic clock. After a 275 year absence the clock was purchased by the Museum and is now displayed in the Octagon Room (formerly known as the Great Room) at the Royal Observatory, Greenwich.