Jonathan Amos
Science correspondent

Possible stages - partial eclipse (top left), diamond ring (top right), Baily's Beads (bottom left), totality (bottom right) and a view of the corona (middle).

Partial eclipse: The Moon progressively covers the Sun's disc. Everything gets darker and darker.

Diamond ring: The last vestige of strong sunshine decreases to a brilliant point of light, as if a big diamond.

Baily's Beads: As the diamond dissipates, any remaining light sparkles through deep valleys on the Moon's edge.

Totality: Day turns to night, but be aware also of changes in temperature, in the wind, in the clouds and in birdsong.

Corona: Your chance to see the Sun's hidden secret - the delicate tendrils of light in our star's outer atmosphere, its corona.

And then it all happens in reverse. Totality is broken by the beads. The diamond reappears and expands the light back to its normal blinding intensity, and the corona is hidden once more.

Simon King
BBC weather presenter and meteorologist

At the start of the eclipse there should be some good clear skies in Mexico but Texas, Austin and Dallas are looking quite cloudy with an increasing threat of some severe weather.

For eastern areas of Texas, severe storms including tornadoes may actually impact travel after the spectacle.

This severe weather could also affect Oklahoma and southern Arkansas but further north in Arkansas, cloud cover is looking a little better up into Indiana where there should be some decent clear spells.

By the time the eclipse reaches northern Indiana, Ohio and northeast portions of the US, there’ll generally be some clear spells but some high level cloud could be a bit thicker to obscure the Sun.

For eastern Canada, Maine and up to New Brunswick, the forecast is looking good with cloudless skies - however in the far east, over Newfoundland, some snow is forecast.

Nadine Yousif
BBC News

Image source, Kate Russo

It was 25 years ago when Kate Russo saw her very first total solar eclipse.

The Australian psychologist was living in Northern Ireland at the time and had always wanted to witness the spectacle in person.

She was in between her Masters and PhD studies in her 20s when, in 1999, the path of totality happened to cross nearby over the southern coast of France.

Today, Russo will watch her 14th total solar eclipse, this time in Uvalde, Texas. She is one of many eclipse chasers who have arrived in North America in recent days.

Experts estimate that more than a million people from inside and outside North America will travel towards the path of totality.

Many are individuals who have combined their love of astronomy, exploration, science and travel into a mission to see as many eclipses in their lifetime as possible.

Some are driven by their love of space and desire to understand the universe around them. Others, like Ms Russo, pursue the indescribable feeling that comes with seeing a total solar eclipse in person.

Sarah Bregel
BBC Future

Image source, AFP

According to Nasa, this event will be different from past total solar eclipses, external.

Scientists say the Sun's corona (its outermost layer) will be more visible than the last total solar eclipse (in 2017) due to the Sun's heightened activity at the time of the event.

The 2024 eclipse will also be visible for nearly two minutes longer than 2017's.

The path of totality is longer, too, meaning the eclipse will be visible to more people, external than the most recent total solar eclipse. About 31.6 million people live in the 200 mile (322km) path of totality – more than doubling the number of people who will be able to see the event since the last of its kind.

Even people who live elsewhere will be able to see the eclipse in some form. "99% of people who reside in the United States will be able to see the partial or total eclipse from where they live," Nasa states on its website.

British scientists in Dallas have teamed up with Nasa to use a polarimeter to examine the directional quality of the corona's light and a spectrometer to look for the behaviour of excited iron atoms.

"During an eclipse, nature gives us a unique opportunity to measure this region with relative ease, and to see the connections between the Sun and solar wind," explained Dr Huw Morgan from Aberystwyth University.

Separately, Ellie MacDonald - a science educator at Kielder Observatory near the Scottish border - has travelled to Texas to live stream the event.

MacDonald, 26, has never seen an eclipse before, and says she’s thrilled to be able to share her footage with followers.

She tells BBC News: "Everyone says how amazing it was in 1999 and a lot of people remember going to see it in Cornwall. Hopefully the livestream will be the next best thing."

Image source, Kielder Observatory

Jonathan Amos
Science correspondent

If an eclipse is all about the Earth, Moon and Sun lining up, then you might think that because the Moon orbits the Earth once a month, the three would line up with that same frequency.

But the Moon’s orbit around the Earth is on a slightly different plane with respect to the Sun and the Earth - it’s tilted by about 5 degrees.

So, it’s only once every 18 months that the three bodies line up perfectly to create a total solar eclipse.

Rebecca Morelle
Science editor

The Moon’s deep shadow lifts off the surface of the Earth way out in the Atlantic Ocean, about 1,000km (620 miles) before reaching the continent of Europe.

But that doesn’t mean it’s a total non-event. In regions like Normandy in France and in western parts of the UK, it should still be possible to witness the tail end of a partial eclipse just before sunset.

For Brits - essentially, if you draw a line from about Fowey in Cornwall to Berwick-upon-Tweed in Northumberland, then everything west of that line might just get a view of the Moon biting the edge of the Sun as it disappears over the horizon.

You'll need to be on high ground and have clear sky. Tricky, I know, but sometimes the gods do favour us.

The Moon's deep shadow, or umbra, is forecast to race across the Earth's surface at more than 2,500km/h (1,500mph).

That’s roughly twice as fast as the speed of sound and faster than a speeding bullet fired by a handgun.

According to Nasa, external, eclipse shadows travel at 1,100mph at the equator and up to 5,000mph near Earth’s poles.

Jonathan Amos
Science correspondent

In ancient times, total solar eclipses were viewed with awe but quite a bit of fear, too.

They were considered a sign, usually a bad one – a harbinger of something awful that was about to happen.

We like to think we live in more enlightened times, but still there’s some nonsense out there.

For example, it’s said you mustn’t cook during an eclipse otherwise the food will become poisonous; or that if you’re pregnant, the eclipse could be harmful to the baby. Total guff.

Eclipses are the product of Solar System “clockwork”. Their only physical influence is to alter the light falling on Earth and to induce subtle shifts in the atmosphere, such as a change in the behaviour of the wind.

The totality begins over the Pacific ocean, with the Moon’s shadow racing north-east to make landfall just south of Mazatlán in Mexico.

The eclipse entered the US just north of Piedras Negras in Mexico and will come to an end over the Atlantic Ocean, but will be partly seen across the pond.

A sunset partial eclipse requiring the use of a solar filter can be seen from western locations in the UK - if you’re lucky enough to have the required equipment

Image source, .

A solar eclipse happens when the Moon crosses paths with the Sun, blocking it from view.

The phenomenon requires the Sun, the Moon and the Earth to be in just the right alignment for the Moon to cast a shadow on our planet.

When this happens, the Moon casts two types of shadows:

• One results in a partial solar eclipse, which covers only part of the Sun.
• The other - and the most spectacular - is called a total solar eclipse, where the Sun is almost entirely covered by the Moon, save for a visible ring of light in the sky.

Jonathan Amos
Science correspondent

Hello and welcome to BBC News’ coverage of what’s expected to be a stunning sky spectacular.

A total solar eclipse will be witnessed today on the North American continent.

The Moon is going to pass in front of the Sun to cast a deep, fast-moving shadow across the face of the Earth. And we’re going to be following it all the way – from Mexico in the southwest to Newfoundland, Canada in the northeast.

It’s been dubbed the Great American Eclipse Part II, because of course the US got to experience a similar event in 2017. But this one promises to be even better, not least because many more people are likely to get to see it this time around.

It’s thought some 32 million US citizens will be able simply to step outside their front door to watch day turn to night. Hundreds of thousands more will cluster along the path of the great shadow.

But a word of caution from the off: Never, ever look directly into the Sun without protection. It’s mega dangerous and could seriously damage your eyes. Remember to stay safe.

We’ll remind you how as the day goes on. Right, I think it’s time to party.