BRITAIN has entered the twilight zone as the moon crosses the face of the sun at the start of the first near-total eclipse visible in the UK for 16 years.

Cloud covering much of the country could spell disappointment for many, but some clear patches are possible where eclipse watchers could be in for an unforgettable experience.

The latest forecast from the Met Office shows relatively cloud-free skies over Wales, parts of the Midlands and the eastern Scotland around Edinburgh.

There is also a possibility that northern parts of the south west peninsula - including Devon and Somerset - will see clouds part in time for the phenomenon.

North of the border, there should also be a bit of brightness towards the bay surrounding Inverness - with rain overnight having cleared and helping to pave the way for some breaks in the cloud this morning.

While people in the South East may miss the full eclipse experience due to cloudy conditions, they will be aware it is happening, according to Met Office forecaster Kate Brown.

"The South East corner is currently overcast and is going to stay that way into the time of the eclipse," she said. "But even if people don't see it happening, they will still be able to sense it getting darker during that time."

As the eclipse develops, the moon will take a larger and larger "bite" out of the sun, covering up to 97% of its face at around 9.30am.

Around the UK the proportion of the sun covered by the moon will increase towards the north, ranging from 84% in London to 89% in Manchester, 93% in Edinburgh, and 97% in Lerwick in the Shetland Isles.

Times will also vary. In London, the eclipse began at 8.24am, reaches its maximum extent at 9.31am, and ends at 10.41am. For observers in Edinburgh, the eclipse started at 8.30am and peaks at 9.35 am.

The last solar eclipse of such significance occurred on August 11 1999, and was "total" - with 100% of the sun covered - when seen from Cornwall.

Another "deep" partial eclipse visible in the UK will not occur until August 12 2026, and the next total eclipse not until September 2090.

Even in overcast areas, no one can predict when there might be a break in the cloud cover, the Met Office said.

It is not unknown for a fleeting break in cloud to occur during an eclipse as the atmosphere cools.

This is one effect scientists at the University of Reading hope to capture as they conduct the largest-yet eclipse weather experiment with the help of sky watchers throughout the country.

Despite the cloud, the event is expected to have a significant impact on the National Grid with a predicted loss of 850 megawatts of solar power from the electricity supply network.

The eclipse produces a 100-mile-wide "totality" shadow path that crosses the North Atlantic and covers only two land masses, the Faroe Islands between Scotland and Iceland and the Norwegian archipelago of Svalbard.

A total eclipse can be an eerie and disturbing experience as day turns to night, birds stop singing, and the sun's shimmering corona atmosphere is revealed.

Away from the totality path, the sun is partly obscured. A partial eclipse will be visible across a large part of the northern hemisphere, including the whole of Europe, Greenland, Newfoundland, northern Africa and western Asia.

Experts have issued repeated warnings to eclipse watchers not to look directly at the sun because of the real danger of permanent damage to eyesight.

Robin Scagell, vice-president of the Society for Popular Astronomy (SPA), who is travelling on the P&O cruise ship Oriana to witness the total eclipse, said: " A partial eclipse is more risky by far than a total eclipse because people don't realise that even looking at a thin sliver of sun is dangerous.

"It's absolutely true that there is a serious risk to people's eyesight. If people can't find a way to view the eclipse correctly, then they shouldn't look because they're likely to damage their eyes."

Together with the SPA, the Royal Astronomical Society has produced a booklet on how to view the eclipse safely.

Popular methods involve projecting an image from a telescope or binoculars on to a piece of white card, using a mirror to cast the image on to a wall, or making a pin-hole viewer from pieces of card or a cereal box that acts like a lens.

Two organised events are taking place in London, where members of the public are being given the chance to view the eclipse using specialist equipment.

One is being hosted in Regents Park by the Royal Astronomical Society and a group of amateur sky-watchers called the Baker Street Irregular Astronomers. The other takes place at the Royal Observatory, Greenwich, assisted by the Flamsteed Astronomy Society.

Several tour operators have organised "total eclipse" trips to the Faroe Islands and Norway.

Rosemary Sloggett, managing director of The Independent Traveller, which has taken 133 eclipse-watchers to the Faroe Islands in a specially chartered airbus at a cost of £2,500 per ticket, said: "The response has been absolutely enormous. A lot of people travelling with us are experiencing their eighth, ninth or 10th eclipse. I think once you've seen one total eclipse, it's something that gets under your skin."

Budget airline easyJet said passengers on three of its flights to Reykjavik in Iceland would have a grandstand view of the total eclipse.

Flights EZY 2295 and EZY 1805, departing from Luton and Manchester at 7.45am, and EZY 6747 from Belfast at 8.05am were passing almost directly over the Faroe Islands during the event.

The National Grid said the impact of the eclipse would be offset by large numbers of people leaving their homes to witness the event.

As a result, it was expecting a net 200 megawatt drop in demand at 9.30am, equivalent to the typical electricity usage of Glasgow.

Jeremy Caplin, forecasting manager at National Grid, said: "This loss of solar is entirely manageable and will be largely offset by demand suppression. We started planning for this in May last year and have a range of tools in place to manage any effects of the eclipse and balance the network, including demand side services and extra generation."

The effect on solar power is likely to be greater in other parts of Europe which depend on the sun for electricity generation more than the UK does .

Solar panels feed large amounts of electricity into the power grids of Germany, Italy and France. In the summer, up to 40% of Germany's energy comes from its solar farms.

The last European eclipse occurred before the proliferation of solar power, so experts are somewhat in the dark over what will actually happen.

Scientists hope tomorrow's eclipse will help them test their models of how solar farms are likely to behave.

Professor Alessandro Abate, from Oxford University's department of computer science, said: "While the impact over the UK is not likely to be as substantial as for other European countries, this eclipse is a rare opportunity to challenge in a worst-case scenario the mathematical models we are developing to predict the behaviour of large populations of solar panels."

Members of the public have been recruited by scientists at the University of Reading to help them study eclipse weather - changes in the atmosphere caused by the sun's rays being temporarily blocked out by the moon.

The National Eclipse Weather Experiment (NEWEx) will draw on observational data recorded by an army of "citizen scientists" across the UK.

There are anecdotal reports of an "eclipse wind" - a breeze that appears as a solar eclipse reaches its peak - and breaks in the cloud appearing as the atmosphere cools.

Professor Giles Harrison, head of the Department of Meteorology at the University of Reading, who is leading the experiment, said: "This is the first big partial eclipse to happen in the UK since 1999, and the next one isn't until August 2026, so this is a once-in-a-generation opportunity.

"By observing what happens on Friday we are effectively turning the skies of Britain into a giant weather lab, giving us a rare chance to see what happens when you 'turn down the sun'.

"This will give us a precious insight into how the sun influences the clouds and wind, as well as more obvious effects, such as temperature. By improving our understanding of how the weather works, we're better able to predict it, meaning scientists can further improve weather forecasts."

The amateur observations will be combined with other data to provide the most detailed picture of the weather effects of an eclipse ever assembled.

Anyone wishing to take part can find full details from the University of Reading eclipse website, http://www.met.reading.ac.uk/outreach/eclipse_2015.html Total solar eclipses can be seen somewhere on Earth every 18 months on average, but are considered rare events that recur at any given location just once every 360 to 410 years.

A solar eclipse takes place when the Earth, moon and sun are aligned and the moon's shadow touches the Earth's surface.