The Royal Observatory is where the Prime Meridian is.
The Camera Obscura: This camera obscura is housed where the astronomer Royal John Flamsteed had a camera obscura to observe the sun. This was an early time, using a telescope and a movable screen. Later the fifth astronomer Royal, Nevil Maskelyne, placed the camera in the turret of Flamsteed house. It was just like the one you are visiting today, with a lens and a mirror in the turret projecting an image down onto a viewing table.
Developments through the centuries with mirrors and lenses transformed the camera obscura from a darkened room into a portable instrument which was the forerunner of the modern camera.
This Long Telescope Tube is a replica of the kind used in the Octagon Room until 1765. The angle of vision was adjusted by moving the tube up or down the rings of the ladder fixed against the window.
The Dolphin Sundial (1977). The pointer of the sundial is formed by the tips of both dolphin’s tails, which almost meet. The tails cast a shadow on the dial plate that has engraved curves, representing the hours.
Throughout the Observatory you can find the Prime Meridian line.