Solar spectacle on horizon

May 17, 2012

A partial solar eclipse will be lighting up Bay Area skies early Sunday evening, and as luck would have it the weather is supposed to cooperate.

Between 5:16pm and 7:40 pm, the moon will pass in front of the sun in an alignment not seen in 18 years. During the annular solar eclipse, the moon will form a “black hole” in the center of the sun with sunbeams shooting out from the sides.

“You won’t be able to see a perfect ring in the Bay Area, but you will see a crescent,” said Jonathan Braidman, an astronomy instructor at Chabot Space and Science Center in Oakland. “Because the sun will be setting at this time you probably want an unobstructed view of the Southwestern horizon as much as possible.”

Word of warning: Don’t look directly at the sun-moon spectacle, as the ring of sunlight is blindingly bright, even though 94 percent of the sun’s disk will be covered.

“No one is going to completely not look,” said Braidman. “So all we can do is ask people not to look directly at the sun.”

A safe way to experience this rare event in all its glory is to visit one of the Bay Area’s viewing events where special goggles and solar telescopes will be on hand (see below for a listing).

There are also a number of DIY techniques, including using #14 Welder’s Glass or some other type of approved solar filter. You can also create a pinhole camera, or for fun visual effects try looking at the way light is scattered through tree leaves. You can also make a solar projector by crisscrossing your fingers waffle-style. Through the gaps, rays of light will have the same shape as the eclipsed sun.

The maximum viewing time, when the moon is most completely blocking the sun, is 6:30pm.

Photo by NASA.

The eclipse is occurring along the “path of annularity,” a 186-mile wide zone stretching from eastern Asian, across the Pacific to the Oregon border, and then southwest into Texas. So consider yourself lucky to be a part of it. Clear skies are expected on Sunday, which is fortunate because fog or clouds would certainly put a damper on things.

This unusual sun-moon alignment is part of the Saros cycle, equal to every 18 years and 11.33 days. That means you won’t be celebrating this one again in Northern California until 2030.

Spend some time looking around at wildlife during the event if you get the chance. Braidman said wildlife might get a little confused.

“These events are pretty rare, so I’d assume this kind of thing would really throw off wildlife in a way,” he said. “They might think it’s getting darker a little sooner.”

After the annular eclipse on Sunday comes a partial lunar eclipse on June 4, in which the moon will be covered one-third by the Earth’s shadow. The portion inside the shadow will be illuminated by sunlight refracted through the Earth’s atmosphere and will have a dimmer, reddish hue.

The following day, June 5-6, will be a “Transit of Venus,” among the rarest of predictable astronomical phenomena. Venus passes between the Earth and the sun, and is visible as a small, darkened disk traveling across the sun.

And mark your calendars for this: a total eclipse is coming our way on Nov. 13.

Fun Facts from NASA:

* Every eclipse begins at sunrise at some point in its track and ends at sunset about half way around the world from the start point.

* Eclipse shadows travel at 1,100 miles per hour at the equator and up to 5,000 miles per hour near the poles.

* Partial solar eclipses can be seen up to 3,000 miles from the track of totality.

* Before the advent of modern atomic clocks, studies of ancient records of solar eclipses allowed astronomers to detect a 0.001 second per century slowing down in Earth’s rotation.

* Local temperatures often drop 20 degrees or more near totality.

* During totality, the horizon is illuminated in a narrow band of light, because an observer is seeing distant localities not under the direct umbra of the Moon’s shadow.

* Only partial solar eclipses can be observed from the North and South Poles.

Spots to view the partial solar eclipse:

The San Francisco Amateur Astronomers is setting up on the Marina green and will provide solar telescopes for viewing starting at 5pm.

The Foothill College Observatory in Los Altos will be open for the eclipse and the Venus transit with the Peninsula Astronomical Society on hand to answer questions.

The Mount Diablo Astronomical Society will have solar telescopes available for viewing at the Juniper campground parking area. There is a $10 park entry fee.

Lassen Volcanic National Park is a bit of a trek, but if you can make it the show there should be quite memorable. Rangers will offer a one-hour program at the Kohm Yah-mah-nee Visitor Center beginning at 3pm and will sell eclipse glasses.

Unfortunately, the Chabot Space and Science Center is sold out — already. But it’s open for the lunar eclipse and the transit of Venus.


About the Author

Alison Hawkes was a Bay Nature editor from 2011-2017. Before Bay Nature she worked in journalism for more than a decade as a former newspaper reporter turned radio producer turned web editor with each rendition bringing her closer to her dream of covering environmental issues. She co-founded Way Out West, a site dedicated to covering Bay Area environmental news.

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