Solar eclipse to set over eastern U.S.

Dennis di Cicco captured this 1973 annular eclipse over Costa Rica in an image sequence that he combined with an earlier photo of the landscape.

By Richard Stenger
CNN Sci-Tech

(CNN) -- A partial solar eclipse will be seen, where weather allows, from the eastern United States around sunset local time on Friday. Earlier in the day, the spectacle will be observable from much of North and South America. And in a small part of Central America, it will be seen as a rare annular or ringed eclipse.

This partial solar eclipse, in which the lunar disk obscures a fraction of the sun, will be the first sighted from North America since December 25, 2000.

In the Eastern time zone, the event should be visible just before twilight, as the sun dips below the horizon. Forecasts of cloudy skies could dampen the viewing prospects.

Astronomers caution onlookers to use special optical filters or projection devices to look at a partial or annular eclipse, as viewing with the naked eye or improper protection can cause serious eye damage.

"Viewers across the southern tier of states will enjoy the best show, with the moon blocking out roughly 40 to 60 percent of the sun's disk in the Southeast," says Robert Naeye of the Astronomical Society of the Pacific.

EXTRA INFORMATION For more detailed information on eclipse-viewing times and phases visible from cities in the Americas, visit this NASA-affiliated site.

"As one moves further north, the moon's coverage of the sun decreases. In the upper Midwest and Pacific Northwest, the coverage will be 10 percent or less."

The eclipse will not be seen from New England and most of Canada. Hawaii should have the best view in the United States. In the morning there, local time, when the eclipse shadow passes over the islands, the moon will block more than 70 percent of the sun.

Sightings of the partial eclipse phases will last from minutes to hours, depending on the location of an observer.

Annular eclipse to the south

Weather permitting, eclipse watchers in Costa Rica and a sliver of Nicaragua will catch a glimpse of the annular solar eclipse, in which the sun appears as a bright ring of light around the silhouette of the moon.

The moon will appear to pass directly in front of the sun for as long as several minutes. But the lunar disk, approaching the most distant point in its orbit around Earth, will not entirely block out the sun.

The annular eclipse shadow will become visible from the Pacific near the international date line in the morning; appear to race 8,000 miles (12,800 kilometers) in less than four hours; and disappear from the sight of viewers in the Caribbean at sunset.

Shortly before its finale, the narrow eclipse shadow, only about 90 miles (144 kilometers) wide, will make its only major landfall. San Jose, the capital of Costa Rica, lies just inside the annular shadow path.

Since the moon will not appear to block the entire sun, the dimming effect will seem negligible at best for most viewers.

Always use proper protection

Astronomers caution that observers should never look at a partial or annular eclipse with the naked eye, binoculars, cameras or telescopes without specialized solar filters.

How the sun will look from various cities during mid-eclipse. A safe solar filter is mandatory to view the sun without risking eye damage.

"The eclipse itself is no more dangerous to view than the sun is on any other day. The only difference is that human curiosity impels some people to stare directly at the sun during an eclipse and this can cause permanent damage to your eyesight," said Fred Espenick, an eclipse expert with NASA.

Solar scientists urge the use of protective optical devices or projection devices to watch the celestial show. They include everything from No. 14 arc-welders glass and Mylar filters to a simple pinhole projector.

"Take two pieces of cardboard or thick paper. Prick a pinhole in one. Then stand with your back to the sun and let the sunlight pass through the hole and onto the other sheet," Naeye said.

"You'll get a small but distinct inverted image of the eclipsed sun. A large hole gives a bright but fuzzy image while a small hole yields a dim but sharp image."