A millennium monument to time
A sundial in Blackfriars
One of three polar sundials, designed by Piers Nicholson, and built by the Royal Engineers in late 1999 for the Tylers and Bricklayers Company of the City of London.
Noon at Blackfriars 
Sundials measure time by the Sun. On a sunny day, the shadow of the oxhead gnomon on this sun dial indicates the time. The Roman numbers show Winter time while the Arabic numerals show Summer time.
Noon is when the Sun is highest in the sky. Noon at Blackfriars is 24 seconds later than noon at Greenwich.
The time between successive noons varies by as much as 30 seconds from 24 hours due partly to the Earth? orbit being in a different plane from the plane of the equator and partly due to the Earth moving at different speeds as it goes round the Sun on its elliptical orbit.
Sundials on the Internet is a web site which explains the difference between Sun time and clock time and where you can find out more about the technicalities of sundials.
Submitted by: Andrew Hunt, 15 January 2007
