- This is the first eclipse to pass over the United States in the 21st century.
- The path of totality spans about 70 miles (113 kilometers) and will pass through 14 states.
- Researchers say the eclipse is important because it will enable astronomers to study the outer realm of the Sun.
On Monday, August 21, for the first time in 99 years, a
total solar eclipse will march across the entire United States.
"The Great American Eclipse" will cast a shadow
over the whole country, moving diagonally from Oregon in the northwest to South
Carolina in the southeast.
Here are some facts
on this eclipse, and what makes it so unique:
This is the first eclipse to pass over the United States in
the 21st century.
It is the first total eclipse on American soil since 1991,
when one was visible from the Big Island of Hawaii.
But it has been 38 years since the mainland United States
glimpsed a total eclipse. The last one was in 1979, and that swept only a
handful of northwestern states.
Having a total solar eclipse move across entire the United
States is quite rare. The last time it happened was in 1918.
A different kind of eclipse -- called an annular eclipse, or
"Ring of Fire" eclipse -- did cross the
United States from coast to
coast in 1994.
Because the Moon was near its farthest point from Earth at
that time in its orbit, it blocked about 94 percent of the Sun's light.
Solar eclipses occur when the Moon moves between the Earth
and the Sun, blocking light from the Sun.
Total solar eclipses happen because the Sun's diameter is
400 times wider than the Moon's, but it is also 400 times farther away.
From Earth's perspective, this geometry makes the Sun and
Moon appear to be the same size.
When the two line up just right, the Moon obscures the
entire Sun, and the skies go dark.
These total eclipses happen every 12 to 18 months somewhere
in the world, often over the open ocean since most of the Earth is covered by
water.
The partial phase of the Great American Eclipse begins over
the Pacific Ocean at 8:46 am local time (1546 GMT).
Unless it's cloudy, Lincoln Beach, Oregon, will be the first
location in the continental US to see the eclipse, beginning at 9:05 am (1605
GMT), according to NASA.
"Totality" -- the term for when the Moon
completely blocks out light from the Sun -- begins near Lincoln Beach, Oregon,
at 10:16 am Pacific time (1:16 pm Eastern, or 1716 GMT).
The path of totality spans about 70 miles (113 kilometers)
and will pass through 14 states.
"Its longest duration will be near Carbondale,
Illinois, where the Sun will be completely covered for two minutes and 40
seconds," says the US space agency.
The total eclipse ends at 2:48 pm (1848 GMT) near
Charleston, South Carolina.
Then, the partial eclipse resumes as the Moon moves out of
the Sun's way. The event ends when the lunar shadow leaves the United States,
at 4:09 pm (2009 GMT).
The entire eclipse will take a total of four hours, four
minutes to make its way across the nation.
Hundreds of millions of people will fall under the shadow of
the eclipse, since the whole country will be darkened -- some parts more than
others.
About 12 million people live in the path of totality,
according to the American Astronomical Society.
Researchers say the eclipse is important because it will
enable astronomers to study the outer realm of the Sun, known as the corona.
Understanding more about how the Sun works, and how solar
flares emerge, can help protect astronauts in space as well as electrical grids
on Earth.
To avoid eye damage,
experts say everyone should wear special solar glasses or use darkened welder's
glass when looking at the Sun.
The light from the
Sun can burn the retina, leading to permanent or long-term damage and blind
spots in one's center of vision.
Another option, to avoid looking skyward, is to make a
pinhole in a sheet of paper or cardboard, and project the Sun's image onto
another piece of paper.
