A total solar eclipse happens when the moon passes directly between our planet
and the sun, as seen from a particular place on Earth.
For a few minutes of "totality," the sun appears to be blotted out. And so for
those in its path, the eclipse promises a spectacle - weather permitting, of
course.
"What you would see is a sort of halo of light around the sun," says Apostolos
Christou, a research astronomer at Armagh Observatory in Northern Ireland.
"This is called the solar corona, it's made up of streams of particles that emanate
from the sun," he continues. "That's usually quite bright in absolute terms,
but we can't really see it most of the time because the disc of the sun is so
much brighter. You would probably also see some of the brightest stars and planets
that happen to be on the sky at that time."
On average, any one spot on Earth will see a total eclipse only rarely - perhaps
once every hundred years or so, though occasionally, two consecutive eclipses
will cross paths at the same place.
But total eclipses are actually fairly common overall, with one visible somewhere
on earth every couple of years.
So the era of modern travel has given rise to a new breed of eclipse enthusiasts. "Eclipse
chasers," as they're known, travel the world to catch a glimpse.
Take Olivier Staiger, a Swiss limousine driver. He's now in Egypt to see his
10th total eclipse. Every one is different, he says. And he remembers his first,
in November 1994, as being "like a first love."
"So I went to Brazil, the fantastic waterfalls of Iguacu was one of the places
where you could see it," he says. "And I saw it, it was really overwhelming.
I was on my knees and whispering, 'Oh, my God.' This was really a breathtaking
and stunning event. And that was where I decided to travel and see other ones."
It's not surprising then, that countries along the eclipse path are taking advantage
of this opportunity. Libya, Egypt, Turkey, and the Greek island of Kastellorizo
have all drawn thousands of tourists for the event.
But aside from the spectacle and the tourist dollars, solar eclipses are of scientific
value, too.
"Nowadays, the eclipse can be used to study more about its effects on the Earth
and its atmosphere rather than [to study] the sun itself, which was the historical
importance of them," says Andrew Norton, who teaches astronomy at the Open University
in the United Kingdom.
He says scientists, for example, can use the total eclipse to study so-called "shadow
bands."
"Shadow bands is a sort of optical interference effect just before and just after
the total eclipse, when you have a narrow edge of the sun visible," Norton says. "This
narrow source of light can give you this optical interference effect where you
get very faint alternating bands of bright and darkness that chase across the
landscape as the eclipse moves. Studying those can tell you about the structure
of the Earth's atmosphere and the movement of pockets of air of different temperatures
in the atmosphere."
Aside from those able to see the total eclipse, a partial eclipse will be visible
along a much broader area in Africa, Europe, and Central Asia.
But for anyone planning to watch on March 29, a word of warning from Armagh Observatory's
Christou: "Don't forget - never view the sun without the appropriate filters.
You watch a solar eclipse with an unaided eye at the wrong time for one second
[and] you're blind."
It's safe to look when the sun is completely blotted out. That part - "totality" -
will last anywhere from one to four minutes, so for those in the right place,
there should be enough time to enjoy the eclipse without risking your eyesight.
