Solar eclipse: expert explains rarity and how to view it

People across England have a rare chance to experience a partial solar eclipse this week, when the Sun will be almost entirely blocked by the Moon. 

Professor Mike Lockwood, Professor of Space Environment Physics and former President of the Royal Astronomical Society, comments on the rarity of the eclipse, the best way to view it, and the history of eclipse observations.  

For interviews, contact the University of Reading Press Office on 0118 378 5757 or pressoffice@reading.ac.uk.  

Professor Mike Lockwood, University of Reading, said: “Tomorrow evening’s eclipse is a partial one, with around 90% of the Sun set to be obscured. This means the Sun will be reduced to a very thin crescent. Eclipses take place every 16-18 months somewhere on Earth. For any one place , a total eclipse will happen only once every 400 years on average. For 90% totality, like tomorrow in the UK, they occur once every few decades, so tomorrow may not be a once-in-a-lifetime event, but it will only happen two or three times in a lifetime.    

"For people wanting to view the eclipse, sunglasses are useless in this instance, and should not be used. Even with 90% of the Sun covered, the remaining sliver still gives off enough infrared and ultraviolet radiation to seriously damage the eye, and sunglasses or degraded or scratched specialist glasses will not block this. Because they make everything look dimmer, the pupil actually opens wider, letting in more of this harmful light, and the retina has no pain receptors to warn when damage is happening. The best and safest way to view the eclipse is by making a pinhole camera and projecting the image onto a screen, so they are never looking directly at the Sun. To do this, cut a big hole in cardboard and cover it with aluminium kitchen foil and make a pin prick in the foil of 0.5-1 mm in diameter." 

"As well as looking at the eclipse itself, stargazers should observe the patterns of light in the sky and the shadows cast – they will look quite strange. Small gaps, such as those between leaves, will cast tiny crescent shapes on the ground instead of round blobs of light. This eclipse is for a low sun that the human brain will see as particularly large, but it is an optical illusion, as objects near the horizon simply look bigger to us than when they are high in the sky. 

“By coincidence, 12-13 August is the peak of the Perseid meteor shower. This is when Earth moves through the dust trail left by Comet Swift-Tuttle, which orbits the Sun once every 133 years. By midnight, stargazers might see a few long “grazer” meteors, but the peak will be at 2-5 am when meteors will occur every 1-2 minutes. 

“At the University of Reading, we study eclipses for a number of reasons. We recently investigated an eclipse observation recorded by a monk, Matthew Parris, in St Albans on 14 May 1240 just after sunrise. We were able to show that the slowing of Earth’s rotation, due to tidal friction, since 1230, has lengthened a day by about one millisecond, which is slightly greater than previously thought.”