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Tuesday, June 26, 2012

Rendezvous With a Shadow

Hidden under a thick pack ice of clouds for much of the year, the Pacific Northwest might not seem the ideal place for amateur astronomy. Weeks can pass without a break in the roiling mass of gray. But such conditions breed a certain combination of patience and optimism ideal for one particular aspect of the science: Eclipse-chasing.

A map of impending solar eclipses shows curving brushstrokes across the earth's surface:

These lines mark the path traced by the pinpoint tip of the moon's shadow, sweeping along the ground as the planet rotates.

If the sun, moon and earth had perfectly flat, circular orbits like CDs lying on a cosmic coffee table we'd have a total solar eclipse at the earth's equator every new moon and a total lunar eclipse every full moon. But contrary to the neat diagrams I studied in the World Book Encyclopedia when I was a kid, the orbits of all the planets and moons in the solar system are elliptical, and tipped at angles like a Calder mobile. (Also, protons and electrons are not, I've since learned, little spheres with pluses and minuses stamped on them as they were depicted in the Encyclopedia. But I still can't help thinking of them that way). The upshot of of all this cosmic complexity is that unless you are willing to stand very still in the same spot for about 400 years, you must travel if you want to see a solar eclipse.

But even getting to the right place at the right time is no guarantee. As any Northwesterner can attest, the weather can ruin the most carefully-laid plans. Imagine waiting months or years and traveling thousands of miles, only to have the appointed time come and go with the entire event hidden from view. It takes a certain strength of both spirit and wallet to keep trying, especially when all you have to show for the experience is photos. Unlike the big game hunter's house with its walls of glassy-eyed animal heads, the eclipse-chaser's home and hard drive are filled with Eye of Sauron-like images of black centers surrounded with flaming rays.

photo: Luc Viatour

Each is equally important to the stalker who bagged it, although in the case of the eclipse-chaser no animals lost any major body parts.

Determining how heroic an effort to make to watch a solar eclipse involves an equation of location congeniality (Honolulu or Mogadishu?), likihood of cooperative weather (San Diego in August, or London in February?) and practicality (Orlando or Easter Island?). Nature supplies an additional factor: Is the eclipse "total" or "annular?"

Because the moon's orbit isn't circular, its distance from earth varies slightly. The difference is not usually noticeable, but it creates two kinds of solar eclipses. When the moon is close to to earth at eclipse time it looms large enough in the sky to completely cover the sun's disk, creating the famous spectacle of a visible corona laced with raging fountains of fiery prominences.

When the moon is further away, it's small enough in the sky to allow a rind of the sun to show around its edges. This "annular" type of solar eclipse is much less of a spectacle, because if even a smidgen of the sun's disk is visible it's so bright that it completely overwhelms the corona.

Totality is the white-tie state dinner of celestial happenings, drawing important scientists, committed amateurs with imposing equipment, and vain celebrities in Learjets. Annularity is more of a local backyard barbecue; a few friends gathered around their telescopes for burgers and beer.

On May 20 of this year one of the brush lines on the map crossed through a swath of countryside in southern Oregon, 500 miles from my home. It was an annular affair, beneath the notice of the elite of the eclipse-chasing world, but worth a day's drive to me.

I needed a long head start on the moon's shadow, since it was traveling approximately ten times as fast as I was. The rain was unrelenting when I left, but I was trusting a forecast that claimed better weather awaited in Ashland. By noon, while I was on Interstate 5 south of Portland, jockeying for position through heavy traffic and clouds of semi-truck spray, the shadow hit the ground in Japan. Observers in Tokyo snapped pictures of the ghostly ring over their city's skies as the shadow began to slice across the Pacific at a thousand miles per hour.

An hour later, as the shadow swung over the Aleutian Islands and starting its turn south toward Oregon, the clouds began to break up and the air warmed. I accelerated over the final stretches of freeway, past columns of circling hawks teetering upwards on the bubbles of almost visibly hot air mushrooming from the lion-colored hills.

Sweating and glancing at my watch, I roared off at the Ashland exit and sped though town to the science museum where Twitter had promised the local astronomy club had set up public viewing stations.

Sure enough the parking lot was filling rapidly with parents who lofted their children onto their shoulders and or held their tugging hands. A line snaked into the museum building for free solar-viewing glasses.

One of the advantages of a solar eclipse is that it is easily seen via projection from a telescope onto a screen. So I had the good fortune to be able to crowd with the children around one projected image after another, watching the spectacle progress.

The shadow duly arrived about a half hour after I did, and the moon began to cross the face of the sun.

The bite got slowly bigger, as wisps of cloud drifted in front of the spectacle.

Soon the sun was nearly gone. The air cooled noticeably, and birds began to sing as though it was dusk.

Finally, the "ends" of the "crescent sun" joined into a ring.

People of all ages crowded around. I realized this was the first "Social Media" eclipse, live-tweeted around the world.

But plenty of people were just as happy to enjoy the spectacle in a more time-honored way:

The next solar eclipse in the Northwest will be the Big Event, totality in 2017. I hope to be there.

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