Crowds gather on the beaches of northern Australia on Tuesday in anticipation of a total solar eclipse that will begin early on Wednesday morning.
People have travelled here to Cairns in Queensland from around the world to witness the eclipse, which will completely block the Sun for about two minutes.
Fred Espenak from NASA's Goddard Space Center is full of excitement.
(SOUNDBITE) (English) NATIONAL AERONAUTICS AND SPACE ADMINISTRATION'S GODDARD SPACE FLIGHT CENTER ASTROPHYSICIST FRED ESPENAK SAYING:
"It's the most spectacular natural phenomenon you can see with the naked eye. It's just beyond description."
But cloud cover could pose a major problem.
(SOUNDBITE) (English) UNNAMED ECLIPSE WATCHER SAYING:
"We've just driven 3,000 km for this weather and to see the eclipse. You can't pick your weather can you? You can pick your friends!"
(SOUNDBITE) (English) ASTRONOMER JAY PASACHOFF SAYING:
"People have looked back at cloud statistics from weather satellites going back 20 years so we know it's a 50/50 or 60/40 chance. We're still hoping for good weather."
A total solar eclipse occurs when the moon passes directly between the Sun and the Earth.
It's expected to cast a shadow 95 miles wide over the northern tip of Australia before moving out into the Pacific Ocean where there is no land in its direct path.