NEW YORK - Millions of people across North America readied for a total solar eclipse on Monday - some gazing anxiously at wayward clouds - as the moon began creeping across the face of the sun in western Mexico before it blocks it out completely.
The total eclipse will be viewable along a path starting in western Mexico and then crossing through the United States and into Canada and will last more than four minutes in some places.
The Mexican beachside resort town of Mazatlan was the first major viewing spot in North America. Thousands of people gathered along the coastal promenade, setting themselves up in deck chairs with eclipse glasses as an orchestra played the Star Wars theme.
In Texas, the south-central region was locked in clouds, but it was a little bit better to the northeast, said National Weather Service meteorologist Cody Snell.
"Dallas is pretty much a 50-50 shot," he said.
The Statue of Liberty is seen during a partial solar eclipse, where the moon partially blocks out the sun, at Liberty Island in New York City, on Monday. (Photo: Reuters)
One festival outside Austin wrapped up early on Monday because afternoon storms were in the forecast. Festival organisers urged everyone to pack up and leave.
The cliffhanging uncertainty added to the drama. But the overcast skies in Mesquite near Dallas did not rattle Erin Froneberger, who was in town for business and brought along her eclipse glasses.
"We are always just rushing, rushing, rushing," she said. "But this is an event that we can just take a moment, a few seconds that it's going to happen and embrace it."
The sky darkens as people take photos with their phones of the total solar eclipse at Sugarbush ski resort in Warren, Vermont, the United States, on Monday. (Photo: Reuters)
Sara Laneau, of Westfield, Vermont, woke up at 4am on Monday to bring her 16-year-old niece to nearby Jay Peak ski resort to catch the eclipse after a morning on the slopes.
"This will be a first from me and an experience of a lifetime," said Laneau, who was dressed in a purple metallic ski suit with a solar eclipse T-shirt underneath.
At Niagara Falls State Park, tourists streamed in under cloudy skies with wagons, strollers, coolers and lawn chairs. Park officials expected a large crowd at the popular site overlooking the falls.
During Monday's full eclipse, the moon slipped right in front of the sun, entirely blocking it. The resulting twilight, with only the sun's outer atmosphere or corona visible, would be long enough for birds and other animals to fall silent, and for planets, stars and maybe even a comet to pop out.
The out-of-sync darkness lasts up to 4 minutes, 28 seconds. That is almost twice as long as it was during the US coast-to-coast eclipse seven years ago because the moon is closer to Earth. It will be another 21 years before the US sees another total solar eclipse on this scale.
Extending five hours from the first bite out of the sun to the last, Monday's eclipse began in the Pacific and makes landfall at Mazatlan, Mexico, before moving into Texas, Oklahoma, Arkansas and 12 other US states in the Midwest, Middle Atlantic and New England, and then Canada. Last stop: Newfoundland, with the eclipse ending in the North Atlantic.
It will take just 1 hour, 40 minutes for the moon's shadow to race more than 4,000 miles (6,500 kilometres) across the continent.
A solar eclipse is seen from Mazatlan, Mexico, on Monday. (Photo: Reuters)
Eye protection is needed with proper eclipse glasses and filters to look at the sun, except when it ducks completely out of sight during an eclipse.
The path of totality - around 115mi (185km) wide - encompasses several major cities this time, including Dallas; Indianapolis; Cleveland; Buffalo, New York; and Montreal. An estimated 44 million people live within the track, with a couple hundred million more within 200mi (320km).
"This may be the most viewed astronomical event in history," said National Air and Space Museum curator Teasel Muir-Harmony, standing outside the museum in Washington, awaiting a partial eclipse.
Experts from the National Aeronautics and Space Administration (Nasa) and scores of universities are posted along the route, poised to launch research rockets and weather balloons, and conduct experiments. The International Space Station's seven astronauts also will be on the lookout, 270mi (435km) up.