The Royal Observatory, Greenwich was commissioned in 1675 by King Charles II.
At this time the king also created the position of Astronomer Royal, for John Flamsteed, to serve as the director of the observatory.
The Observatory is situated on a hill in Greenwich Park in Greenwich, London, overlooking the River Thames.
The Greenwich Meridian runs through the site of the Observatory. It is the line at which the longitude is defined as 0°.