This Saturday, May 5, brings not just Cinco de Mayo but an easy-to-observe astronomical event: the “supermoon.”

Full moons appear to vary in size because of the moon’s elliptical orbit. This year’s perigee moon, or full moon closest to the earth, is on Saturday night. NASA scientists say Saturday’s moon will appear 14 percent bigger and 30 percent brighter than other full moons during 2012.

At 8:35 p.m. the moon will reach it’s largest size. But the best times to witness the full effect of the supermoon is when it rises at 8:03 p.m. and sets at 5:35 a.m., because moons look largest when viewed against the horizon when there are trees, skylines and other objects in comparison.

“It’s called the moon illusion. It is a perceptual trick of the human brain or eye,” says Ben Buress, staff astronomer at the Chabot Space and Science Center. “Your brain is comparing [the moon] to nearby objects, and then comparing it to a different scale when it’s up on its own.”

Skies are supposed to be clear throughout the Bay Area on Saturday. Buress says anywhere with a clear view of the moon during moonrise is a good place to view the event. But for a closer look, or companionship, the telescope at the Chabot Space and Science Center is open to the public on Friday and Saturday evenings.

NASA video: The Super Moon of 2012

View photos here from last year’s super moon.

Tips for photographing full moons.

For more on astronomy visit Buress’ blog at QUEST.

Best Times to Watch Saturday’s Supermoon 4 May,2012Lisa Pickoff-White

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