July 9, 2010:  It's every vacationer's dream: You stretch out on a white sandy beach for a luxurious nap under the South Pacific sun. The caw of distant gulls wafts across the warm sea breeze while palm fronds rustle gently overhead. You take it all in through half-closed eyes.

Could Paradise get any better? This weekend it will.

On Sunday, July 11th, the new Moon will pass directly in front of the sun, producing a total eclipse over the South Pacific. The path of totality stretches across more than a thousand miles of ocean, making landfall in the Cook Islands, Easter Island, a number of French Polynesian atolls, and the southern tip of South America: map, timetables.

Shooting from the Cook Islands, astrophotographer Alan Dyer recorded this South Pacific eclipse on July 22, 2009.

"It's going to be a beautiful sight," says Lika Guhathakurta of NASA's Heliophysics Division in Washington DC. She herself has witnessed more than eight solar eclipses in a variety of environments from busy cities to lonely deserts to remote mountain peaks. "The South Pacific eclipse could top them all."

As seen from space station Mir, the Moon's shadow sweeps across Earth during an eclipse in 1999. [more]

She imagines how the event will unfold: First, the Moon's cool shadow will sweep across the landscape, bringing a breeze of its own to compete with the sea's. Attentive observers might notice shadow bands (a well-known but mysterious corrugation of the Moon's outermost shadow) rippling across the beach as the temperature and direction of the wind shift. The ensuing darkness will have an alien quality, not as black as genuine night, but dark enough to convince seabirds to fly to their island roosts. As their cries subside, the sounds of night creatures come to the fore, a noontime symphony of crickets and frogs.

Next comes the moment that obsesses eclipse chasers: The corona pops into view. When the Moon is dead-center in front of the sun, mesmerizing tendrils of gas spread across the sky. It is the sun's outer atmosphere on full display to the human eye.

"You can only see this while you are standing inside the shadow of the Moon," says Guhathakurta. "It is a rare and special experience."

Because the sun's atmosphere is constantly shape-shifting, every total eclipse is unique. Predicting what any given one will look like can be tricky.

The sun's corona shows itself during the total solar eclipse of March 29, 2006. Credit: Koen van Gorp. [more]

Nevertheless, Guhathakurta is making a prediction. It's based on a new development in solar physics. For the first time, NASA has two spacecraft stationed on opposite sides of the sun. "STEREO-A and STEREO-B are giving us a realtime 3D view of the solar corona, something we've never had before," she explains. "This helps forecast the appearance of the corona during an eclipse."

Inspecting images from STEREO and also from the Solar and Heliospheric Observatory (SOHO), she predicts observers could see four ghostly-white streamers, two on either side of the sun. They will stretch out two to three degrees, forming a gossamer "X" in the sky with a black hole at the crossing point.

"I'm prepared to be wrong," she confesses. "This is the first time anyone has tried to make such a forecast using STEREO data. It will be interesting to see if it works."

Check NASA's eclipse home page for more information about the July 11th eclipse, and stay tuned to Science@NASA, post-eclipse, for images from the path of totality.

Author: Dr. Tony Phillips | Credit: Science@NASA