Christopher Wren's Octagon Room

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Location	Royal Observatory
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The Octagon Room is the oldest part of the Royal Observatory Greenwich.

It was commissioned by King Charles II, designed by famed architect Sir Christopher Wren and completed in 1676.

The Octagon Room, an eight-sided wood-panelled room in the Royal Observatory

The room's eight-sided shape, high windows and lofty position were all designed to provide astronomers with an uninterrupted view of the night sky. The high ceilings also allowed the Observatory to install some of the most advanced clocks of the age.

Clocks set into the dark wood panelling of the Octagon Room at the Royal Observatory

Architecture, astronomy, royal pomp and ceremony: discover the many sides to the Octagon Room as part of your visit to the Royal Observatory.

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Whereas, in order to the finding out of the longitude of places for perfecting navigation and astronomy, we have resolved to build a small observatory within our park at Greenwich, upon the highest ground, at or near the place where the castle stood, with lodging-rooms for our astronomical observator and assistant"
King Charles II

An illustration showing astronomers at work in the Octagon Room of the Royal Observatory. One is looking through a telescope pointed out of the high window on the right hand side

History of the Octagon Room

The beautiful Octagon Room was created by Christopher Wren on the orders of Charles II. It is one of the few Wren-designed interiors that you can still see in London today.

The room's high windows and multiple south-facing views gave first Astronomer Royal John Flamsteed a panoramic view of the night sky. Different instruments could be set up to carry out observations from each window, as this rare print illustrating the interior of the 'Star Room' shows.

The main Observatory building was constructed using the old foundations of Greenwich Castle, which had fallen into decay following the British Civil Wars.

It was a practical solution for a project short of funds. However, this construction made the room less useful when attempting to measure the position of stars.

Astronomers use meridian lines — imaginary lines running due north or south of the viewer — as a reference when making star observations. By repeatedly measuring at what time and what height the stars cross these lines, it's possible to build up an accurate map of the sky.

In the Octagon Room however, none of the walls align with a meridian. Flamsteed in fact made many of his observations from a small brick shed in the garden outside the main Royal Observatory building.

Behind the scenes

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It's about Time

In early 2022 essential refurbishments were carried out in order to safeguard the Octagon Room's unique interior. The room's historic timepieces and astronomical instruments were returned once the work was complete. Here Horology and Scientific Instruments Conservator Daniela Corda examines one of three clock dials designed to fit into the room's wooden panels.

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A window into the Universe

The Octagon Room's large windows aren't just helpful for astronomy. This tall ladder normally acts as a mount for a telescope located within the room. Once refurbishment works were complete, the ladder had to be passed back into the room via the window.

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Finding the perfect angle

This is a quadrant, a movable metal frame with a scale running along the circular edge. A telescope could be mounted to this frame and astronomical measurements taken.

This is a scaled-down version of the one originally used in the Royal Observatory from the 1750s.

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An image showing 'Finding the perfect angle'

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Telling time by the stars

This unusual clock was designed by Astronomer Royal John Flamsteed to help him map the stars. It was made in 1691 by Thomas Tompion.

Instead of a conventional 24-hour clock face, the clock divides the Earth’s daily rotation into 360 degrees, subdivided into arcminutes and arcseconds.

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An image showing 'Telling time by the stars'

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Mark of the King

When you visit the Octagon Room, don't forget to look up at the ceiling. Picked out in gold lettering are the initials 'CR', standing for Charles Rex. This is King Charles II, a reminder of the Observatory's original royal patron.