Long-Awaited E-Day Arrives for San Diego’s Eclipse Watchers

The moon will begin sliding across the sun during a solar eclipse at 10:13 a.m. today, dimming the sky here and casting an eerie, six-minute, 53-second shadow across the Gulf of California later this morning.

Since coastal low clouds threaten to obscure the view, astronomers have two words of advice: Drive inland.

How far? Until there are no clouds overhead. That could be El Cajon or Alpine or farther.

But, if it’s clear, the best bet for viewing in San Diego will be in Balboa Park at the Reuben H. Fleet Space Theater and Science Center, where telescopes will be set up for the public, monitors will show a live televised transmission of the total eclipse from Hawaii and Baja, and astronomers will field questions.

Astronomers now know that solar eclipses occur about 24 times somewhere on the planet each decade. There are never more than five each year, and never fewer than two. The last partial solar eclipse to cast its shadow on San Diego occurred March 7, 1989.

Calculating an eclipse was not always so simple. A few ancient Chinese astronomers were beheaded by their emperors when they failed to correctly predict the eclipse.

But, for today’s astronomers, an eclipse is somewhat ho-hum, though it may be exciting for the rest of us.

“There’s not a whole lot of research or science done during an eclipse anymore because there’s really not that much left to learn. It’s more of an aesthetic thing, especially to amateur astronomers,” said Greg Cade, a board member of the San Diego Astronomy Assn. “It’s just a neat event.”

And it’s the kind of event that has made money for the shrewd entrepreneur. Those in Baja California Sur state will be treated to a spectacular view of the total eclipse, as well as hats, T-shirts and umbrellas stamped with the official “Eclipse 1991” logo.

In San Diego, the view will not be as dazzling, nor has merchandise swamped the shops. But the Space Center has done a brisk trade in eclipse-viewing glasses. By the end of the day Wednesday, 4,000 pairs of protective glasses had been sold, said Connie C. Meyers, spokeswoman for the Space Center.

“This (eclipse) has gotten so much interest because the path is crossing over major resort areas in Hawaii and Mexico,” said Ronald Angione, director of San Diego State University’s Mt. Laguna Observatory and chairman of the astronomy department. “It’s a marketer’s dream.”

The moon’s 139-mile-wide shadow will first touch the Earth at sunrise over the Pacific Ocean, about 300 miles east of the International Date Line. Four and a half minutes later, traveling at 16,000 miles per hour, the shadow will hit Hawaii.

Traveling eastward, the shadow will have grown to 160 miles wide when it hits the Gulf of California. In Baja California, observers will experience almost seven minutes of darkness when the moon blocks the sun.

Mistaking this for night, roosters usually crow. And the temperature drops. The sun’s corona, or outer atmosphere, will emerge like a feathery halo. And, as the moon moves out from in front of the sun, there will be sparkling bits of light, called Bailey’s Beads. These flashes are caused by light pouring through the mountains and valleys of the moon.

Locally, however, the eclipse will be much less sensational because only 74% of the sun will be blocked. The remaining quarter of the sun is bright enough to lessen the overall effect. Instead of a theatrical darkening, San Diegans will see a dimming of light, much like that of a hazy day.

At 10:13 a.m. in San Diego, if it’s clear, the moon will become visible against the sun’s southwestern edge. As the Earth turns on its axis, the sun travels westward and the moon glides eastward, increasingly blocking the sun.

At 11:30 a.m., 74% of the sun will be obscured. Only light from the sun’s edge will reach the Earth. The moon will continue traveling eastward, revealing more of the sun’s disk, and brightening the sky.

At 12:52 p.m., the last bit of moon will slip away from the sun’s southeastern edge.

The alignment of the Earth, moon and sun will also produce unusually high tides in Southern California. The highest tide today will be 7.8 feet at 9:41 p.m. in San Diego. It is the highest tide this year, and there will be no higher tides for the rest of this century.

Experts warn that eclipse viewers should not look directly at the sun. Even at the height of the eclipse, the sun’s rays can permanently damage the retina in just a few seconds, and this damage is irreversible.

Viewers without special glasses can construct a pinhole camera with just two pieces of cardboard to provide safe viewing. Punch a one-eighth-inch hole in one card, and allow sunlight to shine through it and fall on the second, held two to three feet behind it.

Alternatively, eclipse watchers can punch a small hole in one end of a cardboard box and allow the sun’s image to be projected onto the opposite end. To watch, the box is held over the head.

Under no circumstances should the eclipse be observed through conventional sunglasses, smoked glass or exposed photographic film, experts said. Irregularities in the coatings can allow damaging light rays to pass through such objects.

However, welders’ goggles or welders’ glass with a rating of at least 14 can be used safely, most experts say.

During a March 7, 1970, eclipse over the southeastern coast of the United States, 145 cases of eye burns were reported, Angione said. Of those cases, 60% said they had looked directly into the sun with no protective eyewear. The others said they used improper techniques such as looking through sunglasses, exposed film, smoked or tinted glass, or reflections in the water.

Times staff writers Thomas Maugh and G. Jeanette Avent contributed to this report.