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'Great American Eclipse': Sky Show Will Dazzle U.S. Two Years From Now

Two years from now, on Aug. 21, 2017, North Americans will get an opportunity to observe nature's greatest sky show.

Two years from now, on Aug. 21, 2017, North Americans will get an opportunity to observe nature's greatest sky show.

Picture this: The day starts off bright and sunny. Then, a bit later, you begin to notice that, although it is still sunny, the day doesn't seem quite so bright. And still a little while later, it almost seems like some big storm is brewing. Then, suddenly, and without any warning, the midsummer day turns strangely dark.

A few stars come out. Birds and animals become confused and quickly head home to sleep. Night insects begin to chirp. All around the horizon, there is a strange yellow-orange glow resembling a weird sunset. And meanwhile, up in the sky where the sun should be, there appears instead a jet-black disk surrounded by a softly glowing halo. [Amazing 2015 Solar Eclipse Photos]

The European Space Agency's Proba-2 satellite captured this view of the Image:European Space Agency Astronaut Sam Cristoforetti (@AstroSamantha)

Then, just as suddenly, the sky brightens up. The stars disappear, birds and animals awaken, and the sun returns.

What you have just witnessed is a total eclipse of the sun.

This total solar eclipse of 2017 will be the first time in nearly four decades that such an event will be visible so close to home. "Close," of course, is a relative term. But for most Americans, this spectacular phenomenon will occur literally in their own backyards.

Contrary to popular belief, total solar eclipses are not particularly rare. Astronomers predict 68 to take place during the present century — one about every 17.6 months. On such occasions, the moon casts its dark, slender cone of shadow (called the umbra) upon the Earth's surface. [How Solar Eclipses Work (Infographic)]

Related: 'Blood Moon' Eclipse Dazzles Skywatchers

The track traced by the moon's umbra can run for many thousands of miles, but it's also very narrow — at most, about 167 miles (268 kilometers) wide. For this reason, it has been calculated that, on average, a total eclipse of the sun is visible from the same spot on Earth only once in about every 375 years.

In recent years, for instance, assiduous eclipse chasers had to travel to remote locations such as Ellesmere Island in Nunavut, Canada (2008), Easter Island (2010) or the Norwegian archipelago of Svalbard (2015).

But Aug. 21, 2017, will mark the first time this century, and the first time since 1979, that a total solar eclipse will cross the contiguous (lower 48) United States (Alaska had its turn in 1990; Hawaii in 1991). And for the very first time, the shadow track — better known as the "path of totality" — will sweep only over the United States and no other country, leading some people to refer to this upcoming event as "The Great American Eclipse."

Map showing the path of totality across the United States for the total solar eclipse of Aug. 21, 2017.Fred Espenak/NASA GSFC

Many Americans taking full advantage of this event's close proximity to their homes will have a golden opportunity to witness firsthand one of the most beautiful and most exciting of nature's sky events. The total eclipse will be seen by an estimated 12 million people who fortuitously live within the totality path. However, the number of people who are within just one day's drive of the totality zone is probably around 200 million. [How to Safely Photograph the Sun (Photo Guide)]

Not since 1970 has there been an opportunity to see a total solar eclipse in such easily accessible and widespread areas of the United States. There have been a couple of limited opportunities, such as in 1972 (Quebec and the adjacent Canadian Maritime Provinces) and 1979 (the Pacific Northwest and Northern Plains), but the areas of visibility were either limited or somewhat difficult to reach. And not until April 2024 will there be another opportunity comparable to that offered on Aug. 21, 2017.

Notable cities inside the totality path include Idaho Falls, Idaho; Casper, Wyoming; Grand Island, Nebraska; Lincoln, Nebraska; Columbia, Missouri; Nashville, Tennessee; Columbia, South Carolina; and Charleston, South Carolina. The metropolitan areas of Kansas City, Missouri, and St. Louis are right on the edge of the totality path.

Warning: Never stare directly at the sun, either with your unaided eye or through telescopes and binoculars, without proper protection. Serious eye damage can occur. Solar eclipse observers and astronomers use special filters to safely observe the sun.

This is a condensed version of a report from Read the full report. Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmer's Almanac and other publications, and he is also an on-camera meteorologist for News 12 Westchester, New York.Follow us @Spacedotcom, Facebook and Google+.

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