A Total Solar Eclipse is Coming August 21, 2017
On August 21, 2017, that shadow will sweep across North America as millions revel in a total solar eclipse. It’s the first one to grace the continental United States since 1979 and the first to run from sea to shining sea since 1918.
Although a total solar eclipse — when the new moon passes in front of the sun and blocks its bright disk — happens once every year or two somewhere in the world, it’s still a rare sight. Roughly 70 percent of Earth’s surface is covered in oceans, causing many to miss the land. Even then, the moon’s shadow might sweep across the isolated deserts of the Sahara, remote mountaintops in the Sierras, or the war zones in Syria. But this August, the shadow will glide across a strip (roughly 4,000 kilometers long and 120 kilometers wide) of solid and accessible ground.
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On Aug. 21, 2017, American skywatchers will be treated to a rare and spectacular celestial show — the first total solar eclipse visible from the continental United States in nearly four decades.
Next year’s “Great American Total Solar Eclipse” will darken skies all the way from Oregon to South Carolina, along a stretch of land about 70 miles (113 kilometers) wide. People who descend upon this “path of totality” for the big event are in for an unforgettable experience, said eclipse expert Jay Pasachoff, an astronomer at Williams College in Massachusetts.
“It’s a tremendous opportunity,” Pasachoff told Space.com. “It’s a chance to see the universe change around you.” [Solar Eclipses: An Observer’s Guide (Infographic)]
The fact that total solar eclipses occur at all is a quirk of cosmic geometry. The moon orbits an average of 239,000 miles (384,600 kilometers) from Earth — just the right distance to seem the same size in the sky as the much-larger sun.
But most solar eclipses are of the partial variety, in which the moon appears to take a bite out of the sun’s disk. Indeed, two to five solar eclipses occur every year on average; total eclipses happen just once every 18 months or so. (Eclipses are relatively rare because the moon’s orbit is inclined about 5 degrees relative to that of Earth. If the two bodies orbited in exactly the same plane, a solar eclipse would occur every month, during the moon’s “new” phase.)
How Solar Eclipses Work: When the moon covers up the sun, skywatchers delight in the opportunity to see a rare spectacle.
Furthermore, the narrow path of totality is often inaccessible to skywatchers — most of Earth is covered by water, after all — so a total solar eclipse that occurs over populated areas is quite special. Indeed, the August 2017 event will be the first one whose totality path lies completely within the United States since 1776, experts have said.
That path goes from the Oregon coast through Idaho, Wyoming, Nebraska, Kansas, Missouri, Illinois, Kentucky, Tennessee, Georgia, North Carolina and South Carolina. While just 12 million people or so live within the narrow band, perhaps 220 million reside within a day’s drive of it, according to Space.com skywatching columnist Joe Rao. [Incredible Solar Eclipse View Shot During Alaska Airlines Flight (Video)]
Pasachoff advises folks to make that drive when the time comes.
“Though the rest of the continental U.S. will have at least a 55 percent partial eclipse, it won’t ever get dark there, and eye-protection filters would have to be used at all times even to know that the eclipse is happening. The dramatic effects occur only for those in the path of totality,” Pasachoff said in a statement.
“If you are in that path of totality, you are seeing the main event, but if you are off to the side — even where the sun is 99 percent covered by the moon — it is like going up to the ticket booth of a baseball or football stadium but not going inside,” he added.