Dial in Londonderry

This conjectural design consists of a vertical direct south facing dial with a horizontal pointed rod gnomon at the top. Spirals were used by the Neolithic people as a sun motif on their megalithic stone carvings, so spirals were used on this dial to indicate the turning of the seasons and a noon line was also incorporated to mark the passing of the first half of every day. On any day, when the sun is due south and at its highest in the sky, the shadow of the tip of the gnomon touches the vertical line at mid-day, twelve noon, which is marked on the dial with the Roman numeral XII for clarity. The length of the shadow, which varies throughout the year, indicates the occurrence of the Eight Calendric Events when it touches the varying sized spirals, the smallest anti-clockwise indicating the cold mid-winter, the largest clockwise the warm mid-summer with a double spiral at the Equinox marking the transition from winter to summer and vice versa. Ref: Michael Harley, www.sundials-ireland.com