A rare annular solar eclipse of enormous size will appear in the continental United States on Sunday for the first time since 1994.
Unlike a spectacular total solar eclipse, which occurs when the moon passes between the Earth and sun and blocks all but the sun’s corona, Sunday’s annular eclipse will leave a visible “ring of fire” surrounding the moon’s dark silhouette.
Instead of the moon moving directly in front of the sun, the moon will be slightly off-center and the effect will be more of a “C” shape instead of a omplete “O,” experts said.
“This is probably the most easily accessible (annular solar eclipse) for people in the Bay Area in their remaining lifetimes. To see the complete ring is rare and they should do it,” Alex Filippenko, an astronomy professor.
Both types of solar eclipses require alignment of the three bodies, but in an annular eclipse the moon is far enough away from Earth that is doesn’t fully obstruct the disk, leaving the slim ring of sunlight.
The event comes two weeks after a “supermoon,” in which the full moon appeared when it was close in orbit to the Earth. Now the new moon is at the far end of the lunar orbit.
The annular solar eclipse begins in Asia, travels across the Pacific Ocean and hits the West Coast near the California-Oregon border and moves southeast through Eureka, Reno, parts of Utah and Arizona, and Albuquerque, N.M., before ending in Lubbock, Texas.
Viewers in a 150-mile-wide swath of the eclipse path — clear skies permitting — should be able to see the full annular effect, where the moon ultimately will cover about 89 percent of the sun, said Paul Doherty, senior scientist at the Exploratorium in San Francisco.
The moon will pass in front of the sun between 5:16 p.m. and 7:40 p.m., with the peak of the eclipse occurring about 6:33 p.m., Doherty said.
“We’re close enough that we get a good partial eclipse,” he said.
Experts warned that no one should look directly at the sun or a solar eclipse because of the danger of permanent eye damage.
Instead, viewers should get specially made solar eclipse glasses available at science supply stores, some museums or on the Internet.
Viewers also can use No. 14 welders glass, which is hard to find because welders do not need glass that dark. Filippenko aid, however, welding supply shops can recommend glass combinations that can be stacked together to allow for the same protection.
Filippenko said it is important that glasses or other material used to view the eclipse specify that it is capable of blocking 99.999 percent of light.
Another easy and inexpensive method to view the celestial event is to create a pinhole viewer by poking a small hole in a piece of cardboard; something the size of a box side will work. A hole poked by a pencil or pen should be enough to project an image of the eclipse on a surface behind it. Doherty suggested a white surface placed about 6 feet behind the cardboard.
Clouds or fog could ruin the chance to witness the event, but conditions appear to be shaping up well.
“It should be good, but no guarantees,” said Suzanne Sims, a meteorologist at the National Weather Service.
The marine layer has been burning off by afternoon, especially in Contra Costa County. Areas closer to the coast could have fog, but that will depend mostly on how much fog develops in the morning, Sims said.
Next up on the celestial calendar: a June 4 lunar eclipse followed the next day by a rare “Transit of Venus,” in which Venus passes before the sun. That event won’t be visible again on Earth for more than 100 years.
To learn more about the science of eclipses and to read more viewing tips, go to www.nature.nps.gov/features/eclipse.