Sundial. Sundial attached to the wall of a church. The sundial measures time using a shadow formed by the spike (gnomon). This shadow moves across the face of the sundial as the Sun moves across the sky. Each of the lines which radiate out from the gnomon denote an hour of the day. The time is read by seeing which line the gnomon's shadow lies on. This sundial shows the time as 9:30, while the clock (upper left) shows 10:15. The difference is due to British Summer Time (BST), when clocks advance an hour from GMT. This is Sherborne Minster, Dorset, England.