Sundial
A sundial shows the current solar time during the day. It does this because the sun appears to move through the sky. At different times in the day when the sun is shining, a shadow is cast in different places on the dial. A person marks the dial with the time at a certain shadow. This lets users easily see the time. There are a few commonly seen designs, such as the 'ordinary' or standard horizontal garden sundial. However, sundials can be designed for any surface where a fixed object casts a predictable shadow. They may be horizontal or vertical or tilted.
Ancient Egypt had sundials. Other cultures developed them further, including the Greeks and Romans.
Sundial Media
SSW facing, vertical declining sundial on the Moot Hall in Aldeburgh, Suffolk, England. The gnomon is a rod that is very narrow, so it functions as the style. The Latin motto loosely translates as "I only count the sunny hours."
A horizontal dial commissioned in 1862, the gnomon is the triangular blade. The style is its inclined edge.
A combined analemmatic-equatorial sundial in Ann Morrison Park in Boise, Idaho, 43°36'45.5"N 116°13'27.6"W
Top view of an equatorial sundial. The hour lines are spaced equally about the circle, and the shadow of the gnomon (a thin cylindrical rod) moving from 3:00 a.m. to 9:00 p.m. on or around Solstice, when the Sun is at its highest declination.
Bowstring sundial in Singapore Botanic Gardens. The design shows that Singapore is located almost at the equator.
World's oldest sundial, from Egypt's Valley of the Kings (c. 1500 BC)
Reconstruction of the 2,000 year old Phoenician sundial found at Umm al-Amad, Lebanon
A Korean sundial (Angbu-ilgu) first made by Chang Yŏngsil in the Joseon period, displayed in Gyeongbokgung.
A London type horizontal dial. The western edge of the gnomon is used as the style before noon, the eastern edge after that time. The changeover causes a discontinuity, the noon gap, in the time scale.
Southern-hemisphere sundial in Perth, Australia. Magnify to see that the hour marks run anticlockwise. Note graph above the gnomon of the Equation of Time, needed to correct sundial readings.
Related pages
Other websites
- Sunbeams and Sundials Children's guide to the sun, the seasons and sundials.
- There is a book from 1319 that talks about sundails
- There is another old book from the 1500's that talks about how to make a sundial. It's written in the Arabic language