Preparing for the 2015 solar eclipse

AT 9.33am tomorrow, the sun will go out, and the world will be plunged into unnatural darkness. That is the way tomorrow’s eclipse is being billed, anyhow. It may not be quite like that, warns astronomer Martin Lunn.

To us here in York, weather permitting, it will certainly appear as if, from about 8.35am onwards, a black shadow (the moon) is taking progressively bigger bites out of the sun. At one point, at 9.33am, up to 91 per cent of the sun will be covered: leaving a thin glowing crescent of fire in the sky.

“It will be a bit like a crescent moon,” says retired pharmaceutical technician and amateur York astronomer Phil Shepherdson. “Just a sliver of the sun will be left.”

According to Mr Lunn, the former curator of astronomy at the Yorkshire Museum, however, that sliver of sun will still be enough for the remaining daylight to seem more or less normal.

During a total eclipse - last seen in Yorkshire in 1927, according to Mr Lunn, although people living in Cornwall got to experience one in 1999 - the sun is entirely obscured, with just the shimmering corona visible as a rim around the black body of the moon.

The last total eclipse of the sun in the UK was in 1999

The air becomes noticeably chilly, and birds stop singing, confused by the sudden apparent transition from day to night.

Tomorrow, that probably won’t happen: not here in Yorkshire, anyway.

“I hate to disappoint anyone,” says Mr Lunn - doing precisely that - “but the sun has to be about 95 per cent obscured before you start to notice anything.

“If you’re an astronomer, you might just notice a slight dimming effect at 9.33am, but for most people, if you go outside then, you wouldn’t know there was an eclipse on. There will be no temperature drop, and I don’t even know if the birds will fly off to roost, as they do during a total eclipse.”

You’ll need to actually observe the sun itself to “see” the eclipse: something that has already got health professionals worried.

Experts have warned there is a real danger of people permanently damaging their eyesight if they look directly at the sun - even if it is just a sliver of fire. “That’s still enough to damage your eyesight,” says Mr Lunn, who now runs his own travelling planetarium, which he takes around schools.

So if you do want to watch the eclipse, make sure you do so safely. Don’t look at it directly: instead, watch using a pinhole camera (see panel) or by observing the sun’s reflection in a car windscreen.

“That’s the simplest method,” says Mr Lunn. “Somebody told me about it donkeys years ago, and I said ‘no!’ But it works!”

Eclipses of the sun are caused by an alignment of the sun and moon as seen from the earth.

The relative sizes of the two celestial bodies, and their respective distances from the earth, mean that when the moon passes in front of the sun, the two seem to be almost exactly the same size. So provided the moon and sun are perfectly aligned, for a few brief moments the moon blocks the sun out completely.

The fact that these events are so rare - the next full eclipse of the sun as seen from the UK won’t be until 2090, although there will be a ‘deep’ eclipse similar to tomorrow’s in 2026 - makes them all the more unsettling.

Little wonder then that to our ancestors, who didn’t understand the science behind what was happening, an eclipse of the sun could cause widespread panic and dread. It must have felt like the end of the world: or as though the gods in heaven were angry. In Vietnam, people believed that a giant frog was devouring the sun, while in ancient China a hungry celestial dragon was thought to be responsible.

According to ancient Hindu mythology, an eclipse occurred when the demon Rahu was beheaded by the supreme deity Vishnu as a punishment for drinking the nectar of the gods. His head flew across the sky and swallowed the sun. It was once common practice in India for people to bang pots and pans and make loud noises during an eclipse to scare the demon away.

Korean folklore tells of the sun being stolen by mythical dogs, while in Europe, the Vikings believed it was eaten by wolves.

Martin Lunn, curator of astronomy for York Museums Trust, right, with Viking re-enactors, George Panagiotakis, ‘Sigurd’, left, and Zoe Durrant-Walker, ‘Leoba’. The Vikings believed that the eclipse was a giant wolf trying to eat the sun

The ancient Greeks believed a solar eclipse was a sign that the gods were angry, and that it heralded disasters and destruction. And here in the UK, in medieval times, an eclipse was often seen as an ill omen. A solar eclipse that darkened the skies 530 years ago coincided with the death of Anne Neville, the wife of King Richard III - and five months later the last Plantagenet king himself was also dead, famously killed at the battle of Bosworth.

Professor Richard Wiseman from the University of Hertfordshire, a leading expert on superstition and psychic phenomena, said: “A solar eclipse is a very unusual event, and one completely outside of our control. Its easy to understand how it could be ascribed to some sort of external agency.

“We like to think things happen for a reason, and if we don’t know what the reason is, we make one up. We say the gods are angry. The search for an explanation leads to superstition.

“In earlier times people would have been more aware of things happening in the sky. The sun is the source of warmth and well-being and when it’s suddenly taken away normal order is broken down.”

Well, don’t worry tomorrow. Normal service will be resumed pretty quickly, with the eclipse over by 10.40am.

How to observe an eclipse safely

A guide to safe eclipse viewing has been issued jointly by the Royal Astronomical Society and Society for Popular Astronomy.

The most important thing is never to look directly at the sun, even through sunglasses or dark material such as a bin liner or photographic negative. Makeshift filters may not screen out the harmful infrared radiation that can burn the retina of the eye.

Here are some safe methods of observing the eclipse.

• Using a mirror. Cover a small flat mirror with paper that has a small hole cut in it. The hole should be no wider than 5mm. Prop up the mirror so it reflects the sunlight onto a pale screen or wall, ideally through a window, to produce an image of the sun just over 5cm across. You will be able to watch as the moon starts to take a “bite” out of the sun, appearing upside down compared with its position in the sky. Do not look into the mirror during the eclipse as this is just as dangerous as looking directly at the su.n

• The pinhole viewer. Make a small hole in a piece of card using a compass or other sharp-pointed implement. Standing with your back to the sun, position another white card behind the one with the pinhole so that the sun projects an image onto it. Never look through the pinhole directly at the sun.

• Colander method: Take an ordinary kitchen colander and stand with your back to the sun holding it in one hand and a piece of paper in the other. The holes in the colander project multiple eclipse images onto the paper.

• Car windscreen. Perhaps the simplest method, says Martin Lunn, former curator of astronomy at the Yorkshire Museum. Simply find a car parked so that its windscreen reflects the sun, then watch the reflection.

Morning glory

Tomorrow’s eclipse will begin at about 8.25am (when the moon will appear to take its first “bite” out of the sun) and will continue until about 10.40am. It will reach its maximum extent in Yorkshire at about 9.30am, when 91 per cent of the sun will be obscured.

Those further north will experience a “deeper” eclipse than those living further south. As seen from Lerwick, in the Shetland Islands, 97 per cent of the sun will be hidden. Londoners, however, will only observe 84 per cent of the sun being hidden.

The last full eclipse visible from the UK was in 1999 – though even then only in Cornwall was the sun completely hidden. The last full eclipse visible from Yorkshire was in 1927, according to Martin Lunn, the former curator of astronomy at the Yorkshire Museum. The next “deep” eclipse like tomorrow’s in which much of the sun will be hidden will be in August 2026 – and the next full eclipse visible from the UK mainland won’t be until 2090.

Tonight in York, there will be an “eclipse” event run by the York Astronomical Society at the Knavesmire from 6.30pm until 9pm at which you’ll be able to learn more about what will be happening tomorrow. Just turn up if you’d like to find out more.

Weather forecast

There is likely to be some overnight fog forming in York tonight: so our chances of observing the eclipse tomorrow may depend on whether it clears in time.

Weather forecaster Andy Ratcliffe of Meteo Group said that, provided the fog had lifted, there should be some breaks in the cloud over York at the time of the eclipse, however. So it all depends on that fog.  Fingers crossed...