A rush-hour eclipse of the Sun brings an unmissable astronomical spectacle to the UK this week that will not be repeated for another decade.
The near-total solar eclipse is expected to bring out hundreds of sky-watchers eager to witness the phenomenon as the moon moves in front of the Sun on Friday.
But experts have warned of the real danger of permanent damage to vision if people fail to take the necessary precautions.
Children, who will be starting school during the eclipse, could be especially at risk. Looking directly at the Sun even if most of it is obscured can result in the retina being burned.
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 begins at 8.24am, reaches its maximum extent at 9.31am, and ends at 10.41am. For observers in Edinburgh, the eclipse starts 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.
Next Friday's eclipse will produce a "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.
Several tour operators have organised trips based around the total eclipse, which will briefly allow the Sun's outer atmosphere, or corona, to become spectacularly visible.
Robin Scagell, vice-president of the Society for Popular Astronomy (SPA), who will be travelling on the P&O cruise ship Oriana to witness the eclipse, described what people can expect to see.
He said: "We won't experience totality in the UK but it will still be a memorable event. Depending on where you are, up to 90% of the Sun will be covered over.
"You'd think everything would go virtually black, but it doesn't, i t's about equal to a fair bit of high cloud in front of the Sun. But it has this eerie quality, especially on a clear day. You think, hang on, it's getting darker, but there are no clouds."
In London, organised events are being held in Regent's Park and the Royal Observatory, Greenwich, where amateur astronomers and members of the general public will have an opportunity to enjoy the eclipse safely using telescopes and solar viewers.
Experts from the Royal Astronomical Society, the SPA, the Royal Observatory, the Royal College of Opthalmologists, and the College of Optometrists together offered advice on safety and warned of the perils of sun-watching.
Mr Scagell pointed out: "Unlike every other eclipse of any size, this one takes place right in the middle of the rush hour. It's not the best time from a safety point of view.
"We've always had this problem with partial eclipses in particular. You need to cut down the light of the Sun by an enormous amount before you can look at it safely.
"Sunglasses are useless and even things like food packing and bin liners that look as if they're made of dense material can let through infrared light and burn your retina.
"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."
He said the partial eclipse coincided with the start of the school day in the UK and break time in other parts of Europe, where the clocks are an hour ahead of GMT.
"A friend of mine tells me there's going to be a problem throughout Europe," Mr Scagell added. "One school in Belgium plans to keep all the children in during the break, so they won't be tempted to look up at the Sun."
The Royal College of Opthalmologists said looking directly at the Sun can lead to retinal burns and may cause significant and sometimes permanent loss of sight.
One case study reported to the college involved a young patient who suffered solar maculopathy - destruction of the centre of the retina caused by solar radiation - as a result of viewing the Sun through a telescope. The patient was left with permanently reduced central vision.
A spokeswoman said: "Whilst a solar eclipse is an amazing and infrequent event, the general public must remember that they should not look directly at the Sun or at a solar eclipse, either with the naked eye, even if dark filters such as sunglasses or photographic negatives are used, nor through optical equipment such as cameras, binoculars or telescopes. There is no safe system to directly view an eclipse.
"Particular care should be taken with children. Children should not be allowed to look directly at the Sun at any time."
Dr Susan Blakeney, from the College of Optometrists, said: "You should never look directly at the sun and that applies when there's a total or partial eclipse as well. This is because the radiation emitted by the Sun is so powerful it may cause a solar burn of the retina."
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.
An ordinary colander can also be used to produce multiple eclipse images on a piece of paper.
On Friday morning the Royal Astronomical Society and a group of amateur sky-watchers called the Baker Street Irregular Astronomers will run a joint free event in Regents Park. Members of the public will be invited to view the eclipse using specialist equipment that makes it possible to see sunspots, and solar prominences and filaments.
A similar event is taking place from 8am at the Royal Observatory, Greenwich, assisted by the Flamsteed Astronomy Society.
Tour operator The Independent Traveller is taking 133 eclipse-watchers to the Faroe Islands in a specially chartered airbus at a cost of £2,500 each. The trip has been fully booked for the past two months despite extra places being added.
Managing director Rosemary Sloggett said: "The response has been absolutely enormous. We started looking at this two-and-a-half years ago with a degree of fear and trepidation, but have had take-up from right around the world, as far afield as Australia, Hong Kong and the US.
"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."
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.
Totality is only visible along a track a few hundred kilometres wide, and away from this path the Sun is partly obscured. Friday's 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.