A solar eclipse darkens American skies

Some observers in the western United States will see the Moon block out most of the Sun’s face May 20, while many others will witness a partial eclipse event.
By | Published: May 11, 2012
A ring of sunlight remains visible at the midpoint of an annular solar eclipse. Although the Moon and the Sun align perfectly, our satellite appears too small to cover the solar disk completely.
Jatin S. Rathod
The path of annularity cuts across the southwestern United States late in the afternoon May 20. Those along the center line will see the Moon block 89 percent of the Sun’s area, but even those outside the 185-mile-wide (298 kilometers) track can still witness a partial eclipse. Astronomy: Roen Kelly

For the first time in 18 years, residents in the western two-thirds of North America will witness the Moon pass in front of the Sun on May 20, creating a partial solar eclipse. And those lucky enough to be within a 185-mile-wide (298 kilometers) track that runs from Northern California to western Texas can experience the “ring of sunlight” that comes with an annular eclipse.

An eclipse occurs when the Sun, the Moon, and Earth line up, with our satellite in the middle. If the three align exactly while Luna lies closer to Earth than normal, observers will witness a total eclipse. But when the Moon lies farther away, it doesn’t completely block out the Sun, so viewers see a ring of sunlight in the sky, known as the “annulus.”

Just one day before the trio’s alignment, the Moon reaches the farthest point in its monthly orbit around Earth. This means it is too small to cover the Sun’s entire disk May 20. Instead, people along the center line of the eclipse will see Luna block out 89 percent of our star’s area.

The annular path begins at sunrise May 21 along China’s southeastern coast and quickly crosses southern Japan. Weather prospects aren’t great in these areas because it’s monsoon season.

As the eclipse treks across the Pacific Ocean, it crosses the International Date Line, meaning the event occurs May 20 in the Americas. The Moon’s antumbra (the part of its shadow beyond where a total eclipse would be visible) reaches land at the Northern California coast between Eureka and Crescent City, with annularity beginning at 6:24 p.m. PDT and lasting 4 minutes, 47 seconds.

After leaving the Golden State, the eclipse tracks southeast into the Nevada desert before crossing into southern Utah and northern Arizona. A spectacular scene will await those at the Grand Canyon, Bryce Canyon, and Zion national parks, even though the Sun stands only 10° above the horizon by this point in the afternoon. As sunset approaches, the Moon’s antumbra zips across New Mexico. The annular eclipse finally ends at sunset slightly southeast of Lubbock, Texas.

With such a wide path of annularity, millions of people will be within a short drive of seeing the event. But many more won’t have to travel at all to at least see a partial eclipse. “Anyone with a clear sky who lives west of a line that runs from western Texas to the western Great Lakes and into Canada will witness the Moon take a significant bite from the solar disk,” says Astronomy Senior Editor Richard Talcott. “Farther east, people can see the Moon nibble on a smaller part of the Sun just before the two set.”

Eclipse viewing tips

  • Don’t view this event without eye protection. Even during the annular phase, the Sun shines brightly enough to damage your retinas if you view it directly. Use only approved eclipse glasses, solar filters, or #14 welder’s glass.
  • Arrive at your viewing site an hour or more before the partial phases of the eclipse begin, especially if you want to photograph the event.
  • Once the Moon covers a large part of the Sun’s disk but before annularity begins, take a look at your surroundings to see the effects of the eclipse, including the tiny solar crescents created by sunlight filtering through any nearby trees.
  • If you want to see a planet during annularity, look 23° east (above and a bit to the left) of the Sun to find Venus.

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