Solar Triple Play
Solar Triple Play: Venus Transit, Solar Eclipse, Partial Lunar Eclipse

Get ready for a celestial sports extravaganza as you’ve never before seen—not all at once, anyway. Coming up in May and June this year is a matchup of three rare and beautiful celestial events, conveniently scheduled back to back to back for your viewing enjoyment.

Game 1: On May 20th, a solar eclipse will darken our skies and dazzle our eyes. From the Bay Area, it won’t appear as a total solar eclipse, but it’s not far off from one either. If you want to see the full force of this eclipse, when the Moon’s disk lines up perfectly with the Sun’s, you’ll need to drive north and park within a swath of territory centered on Redwood National Park along the northern California coast, and inland, east and south, across Lassen Volcanic National Park. Here’s a play diagram to help guide you.

Within the swath of land following the Moon’s deepest shadow track you will experience what is called an annular solar eclipse—the brighter, though less famous sibling of a true total solar eclipse. An annular eclipse occurs when, at the time of this eclipse, the Moon is more distant from Earth than usual, its disk appearing smaller than the Sun’s disk. So, even when perfectly positioned in front of the Sun, a rim of sunlight will shine out from all around the edge of the Moon’s disk, creating a brilliant ring (or annulus) of golden sunlight for a few minutes. You may even look up at the sight and purr, “My precious….”

Here in the Bay Area, the eclipse will be a partial one—though a significant amount of the Sun will be covered, and Earth and sky will dim noticeably. The eclipse begins for us at 5:15 PM (PDT), when the Moon’s disk first touches the edge of the Sun, gradually covering more of it until reaching maximum occlusion at 6:32 PM. The Sun will set while the eclipse is still in progress—but what an unusual sunset we may see!

The second heat of our Solar Triple Play airs two weeks later on June 4: a partial lunar eclipse—a sort of opposite, not-quite-instant replay of the solar eclipse; the yin to its yang. The same close alignment between Sun, Earth, and Moon that produced the solar eclipse produces this lunar eclipse as well, the related events two weeks (or half a lunar orbit) apart.

Set to begin in the wee morning hours on a Monday (as if to mess with our celestial sports viewing schedule), the eclipse technically begins shortly before 2:00 AM—but that’s only the penumbral phase when the Earth’s partial shadow first contacts the edge of the Full Moon.

The better part of this game gets going a few minutes after 3:00 AM, when the Earth’s full, umbral shadow makes contact. Lunar eclipses are a contact sport, so this is when the viewing gets good. At half-time–shortly after 4:00 AM—the eclipse will be at its peak. Being a partial eclipse, only a portion of the Moon is darkened by Earth’s umbral shadow at this time, but it’s still a beautiful sight! The Moon will actually be setting toward the end of the fourth quarter (game time), so the finale of the Moon being obscured by Earth’s shadow will be the Moon obscured by the Earth itself!

And last, but certainly not least in our game line-up: The Venus Transit. In the mid afternoon and early evening hours of Tuesday, June 5th, starting at 3:07 PM PDT, the planet Venus will be making a 300,000 mile dash across the face of the Sun, and we will be sitting in prime stadium seats to see it!

The Venus Transit is both extremely rare and a historic-Hall-of-Fame-worthy celestial event, for it was by observation of Venus crossing the Sun a couple of centuries ago that we were able to calculate the distance between the Sun and the Earth—using, what else? mathematics! By observing the path of Venus across the face of the Sun from different locations on Earth, simple trigonometry was used to triangulate the then unknown Earth-to-Venus and Venus-to-Sun distances—put ‘em both together and you have one Astronomical Unit, the Sun-Earth distance (about 93 million miles!)

And, rarer than the Super Bowl, rarer than the Olympics, the Venus Transit takes place only once in more than a century at alternating intervals of 105 and 120 years. But this phenomenal phenomenon is equipped to provide an instant replay. Well, not quite instant: the century event occurs in pairs, eight years apart. There was a Transit in 2004, so don’t miss this one as it’s truly a last-in-a-lifetime experience!

We’ll be open for observation and fun activities at Chabot Space & Science Center for all three events (click on the Events link below the banner). Hope to see you up here at game time! Meanwhile, keep your eye on the ball, but be sure not to look at the Sun without proper eye protection.

A Celestial Sports Extravaganza: Solar Triple Play 11 June,2013Ben Burress


Ben Burress

Benjamin Burress has been a staff astronomer at Chabot Space & Science Center since July 1999. He graduated from Sonoma State University in 1985 with a bachelor’s degree in physics (and minor in astronomy), after which he signed on for a two-year stint in the Peace Corps, where he taught physics and mathematics in the African nation of Cameroon. From 1989-96 he served on the crew of NASA’s Kuiper Airborne Observatory at Ames Research Center in Mountain View, CA. From 1996-99, he was Head Observer at the Naval Prototype Optical Interferometer program at Lowell Observatory in Flagstaff, AZ.

Read his previous contributions to QUEST, a project dedicated to exploring the Science of Sustainability.

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