'I am moved to tears': Total solar eclipse mesmerises America

For the first time in nearly four decades the US has witnessed a total solar eclipse.

After weeks of anticipation millions of Americans looked skyward through protective glasses, telescopes and cameras as day briefly turned to night.

While the earth, the moon and the sun perfectly line up around every 18 months this time was particularly special because it's one of the rare instances where the eclipse could be seen in populated areas – the first since 1979.

This total solar eclipse was only visible from America where the moon's shadow passed through what's called the path of totality.

It travelled coast to coast, tracing a 113km path across 14 US states, moving from Oregon on the west coast to South Carolina in the east.

Festivals, rooftop parties, weddings, camping trips and astronomy meet-ups popped up nationwide for what NASA expected to be the most heavily photographed and documented eclipse in modern times, thanks to the era of social media.

Whoops and cheers rose from the crowd as totality began at 1716 GMT over Oregon, and similar cries of joy erupted roughly 90 minutes later when the phenomenon ended at 1848 GMT in Charleston, South Carolina.

"It was incredibly beautiful. I am moved to tears," Heather Riser, a 54-year-old librarian from Virginia said as she sat on a blanket in Charleston's Waterfront Park where thousands had gathered on the grass to watch.

• Twitter erupts as Trump stares directly at the solar eclipse

Crowds in Lincoln Beach, Oregon were first to witness the partial phase of the Great American Eclipse, from about 1605 GMT.

Just inland, more than 100,000 people gathered at Madras, Oregon – typically a town of 7,000 – in what experts described as perfect viewing conditions.

In Los Angeles, "oohs and aahs" emanated from the crowd of thousands of people gathered at the Griffith Observatory in the hills above the city as the partial eclipse began.

"This is a once in a lifetime event," 42-year-old Chad Briggs said.

"We have to start eating salad and be healthy if we want to make it till the next eclipse!"

Many had hiked to the site to avoid massive traffic jams. Some watchers had fashioned their own pinhole projectors out of cardboard and scotch tape.

In Mexico, where there was a partial eclipse, astronomy buffs set up telescopes fitted with special sun filters in parks and squares in various cities.

"Put down your smartphone and experience this one emotionally, psychologically, physically, rather than just through the screen," advised prominent US astrophysicist Neil DeGrasse Tyson.

'Sensory overload'

"It is such an incredible, sensory-overload kind of event," eclipse-chaser Fred Espenak, a retired NASA astrophysicist, said of the first total solar eclipse he saw in the United States back in 1970.

In the US capital, where 81 per cent totality occurred, President Donald Trump watched the partial eclipse from the White House with his wife Melania and son Barron.

At one point, Trump glanced skywards without protective eyewear – a big no-no, according to experts.

"Don't look," an aide shouted to him.

He later donned glasses.

'Permanent damage'

Experts warn that looking directly at an eclipse can cause permanent eye damage.

"The damage can really be permanent and right smack in the centre of their vision," said Vincent Jerome Giovinazzo, director of ophthalmology at Staten Island University Hospital, Northwell Health.

The only safe time to look at it is for those within the path of totality - and only during the brief moments when the sun is completely blocked.

Everyone else should use proper solar eyeglasses, which are far darker than regular ones, or make a pinhole projector to see the eclipse while avoiding the glare of the sun.

It's estimated it will be the most photographed, the most watched, and the most studied eclipse of all time.