Wednesday, November 5, 2014

Do sundials still work?

Dr Abe V Rotor
Living with Nature - School on Blog
Paaralang Bayan sa Himpapawid (People's School-on-Air) with Ms Melly C Tenorio
738 DZRB AM, 8-9 evening class Monday to Friday

The author examines the Sundial in Tagudin, Ilocos Sur, built in the 18th century at the town's plaza.

This caliper designed sundial at the College of Engineering, University of the Philippines, Diliman Quezon City is probably the biggest of its kind in the world. Photo by AV Rotor.

A sundial is a device that measures time by the position of the sun. It is like measuring the lengthening shadow of a standing person or a post, calculating the hour of the day in the process. This practice of telling time by the shadow we make is still common today in the provinces. Thus, a trained person tells the time to fetch children in school, to prepare meals, to go home and do his chores.

Telling time with the sundial is not of course accurate. First, it depends on the longitude and latitude of the place, meaning where exactly is the sundial located. This is important to know the position of the sun in relation to the place. Sundials in the south hemisphere are reverse to those in the north hemisphere. Sundials on the equator are marked differently and adjusted as you get closer to the north or south pole.

The other reason for the lack of exactness of sundials is because the earth's rotation around the sun is not a perfect circle; it is elliptical with the nearest distance called perigee and the farthest, apogee. And the pattern is not fixed year to year.

Today, with the introduction of mechanical and electronic devises to tell time, the sundial has been relegated to the museum, and landmarks, like the sundials in Tagudin, Ilocos Sur and the giant caliper-like sundial at UP Diliman. There are however, architecturally designed buildings to tell time by their shadow, such as Taipei 101 building in Taiwan, and sundials equipped with electronic systems that automatically make the necessary adjustments to the mentioned variables.

A typical analemmatic sundial, also known as a 'Human Sundial'. The person acts as the gnomon, standing in the proper position for the month. This sundial has a second, inner dial to show the daylight saving time , which is adopted in a number of countries.

Hemispherical Greek sundial from Ai Khanoum, Afghanistan, 3rd-2nd century BC.

An equatorial sundial in the Forbidden City, Beijing. The gnomon points true North and its angle with horizontal equals the local latitude. Closer inspection of the full-size image reveals the "spider-web" of date rings and hour-lines. The author had a chance to study some of the inventions of ancient China in 1982 and 1985, among them is this sundial.Near the site are surviving instruments to track celestial bodies, the early Chinese being advance in astronomy.

The Giant Sundial of Jantar Mantar in Jaipur, India, also known as the Samrat Yantra (The Supreme Instrument), stands 27m tall. Its shadow moves visibly at 1 mm per second, or roughly a hand's breadth.

This sundial displays a likeness of Father Time. Its motto quotes Robert Browning: "Grow old along with me; the best is yet to be."
Shadow of Taipei 101 in Taiwan. circular park (bottom) acts as the face of a huge horizontal sundial using the skyscraper as its style. The author was a visiting professor at the time the foundation this building, once the highest in the world (taller than the US Empire State and Sear's Towers, and Malaysia's Petronas Twin Tower) during its construction in 1992. 
Millennium Park in uses the shadow of Taipei 101 to mark afternoon hours for the skyscraper's occupants.

Acknowledgement: Photos other than those indicated were derived from the Internet's Wikipedia.

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