UW Today

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March 4, 2004

Web site features pioneer EarthDials from around the globe

News and Information

Join a dozen “EarthDialers” at  http://planetary.org/mars/earthdial  as the modern marvel of the webcam merges with the ancient technology for marking time, the sundial.

The EarthDial Project Web site carries a global network of sundials that, thus far, includes half a dozen in the United States, as well as ones in Spain, Malaysia, Honduras and even Antarctica. The sundial at the South Pole, currently basking in sunlight 24 hours a day, will plunge later this month into six months of darkness.

A project of the Planetary Society, the world’s largest space interest group, Seattle’s Bill Nye the Science Guy, and UW Astronomy Professor Woody Sullivan, the Web site gives viewers a palpable sense of what time is on the globe. “As your eye sweeps across the world map on the screen, you’ll see the shadow angles changing just like the hands on a clock in different time zones,” Sullivan says. He hopes this map will inspire others to set up their own EarthDials in coming months.

The EarthDial Project coincides with exploration by the Mars rovers Spirit and Opportunity, each of which carries a sundial calibrated to Martian solar days (http://redrovergoestomars.org/marsdial/). The motto “Two Worlds — One Sun” is inscribed on project sundials on both planets.

Schoolteachers, observatory staff members and amateur astronomers are among those who responded to a call, first issued last November, to build sundials to EarthDial Project specifications and set up webcams with around-the-clock Internet connections to provide images of the various sundials every 5 to 10 minutes. If a person can’t see a shadow on a particular sundial, then it is probably cloudy. And if the image on the Web is black, it’s probably night.

Each EarthDial is about 32 inches across. The path the sun traces across the sky differs greatly between the Northern Hemisphere, the tropics and the Southern Hemisphere, Sullivan says, so each dial has a pattern appropriate to where it’s located. Outside the standardized main circle, the various sundials include personal touches such as text in local languages and regional icons.

The first set of EarthDials at http://planetary.org/mars/earthdial includes:

• One on the roof of a Fairfax County high school in Alexandria, Va., that has, as part of its Web site, a sophisticated animation of a spinning Earth and time-lapse images of the sun’s shadow across the site during the previous 24 hours (http://www.wsanford.com/webcam/earthdial/composite.html).

• An EarthDial in Antarctica, operated by a researcher at the National Science Foundation’s Amundsen-Scott South Pole Station, that is presently in sunlight 24 hours a day because the Earth’s south pole is tipped toward the sun. Instead of rising and setting, what one sees each day is the sun making a complete circle around the horizon at a constant height. Thus the sundial there has markings like a pie with 24 slices. Eventually, as the Earth tips the other way, the sun will circle down below the horizon, plunging everything into dark for six months. Visitors should note that webcam images are live only for a variable 8 hours a day because of satellite coverage.

• A sundial in Valencia, Spain, of hand-inked ceramic tiles mounted on a stand in a sea-green pond on the grounds of the Astronomical Observatory of the University of Valencia.

• The project’s single dial in Asia so far, built by a 16-year-old student in Penang, Malaysia.

• “ED-1,” or EarthDial-One, the original dial of the project at the Seattle laboratory of Nye, who along with Sullivan and others devised a way for the Mars rovers to be equipped with MarsDials.