Eclipsing the experience

Emily Winterburn, assistant astronomy officer at the Royal Observatory in Greenwich, peers behind the panic about Wednesday's eclipse of the sun

Anybody reading British newspapers over the past few weeks might be watching an eclipse of the sun was a highly dangerous activity, attempted only by the reckless. Certainly the Royal National Institute for the Blind was keen to encourage people to view the sun only by projection, while Professor Liam Donaldson, the government's chief medical officer, went further: suggesting on 28 July that the only truly safe way to view the eclipse was at home, on TV.

To many, this might seem to be an overreaction. I work at the Royal Observatory in Greenwich, answering enquiries on astronomy-related topics. I received a number of calls from baffled members of the public, who remembered being at school in the 1950s (there was a partial eclipse over Britain in 1954) and actually being encouraged by their teachers to view eclipses through smoked glass (something we wouldn't recommend). 'Was this eclipse particularly dangerous?' they wanted to know.

In response to Liam Donaldson's statement, and the growing concern in the media about eye safety and the reliability of solar filters, we at the observatory were flooded with calls from potential eclipse watchers concerned about their eyes. I have taken around 50 calls a day myself. Some were parents, understandably concerned about their child's safety; assuming they would only be safe indoors, and wanting to know the times of the eclipse so they could keep their children inside or in some way distracted. The vast majority, however, were people looking for sensible advice. While they were not prepared to stay indoors and watch the eclipse on TV, the hype had led them to wonder what they should be doing.

People rang worried about safety of viewers, danger to their pets, and heightened risk of crime due to reduced lighting. More than anything, people were surprised to hear that the sun is no more dangerous during an eclipse than on a normal sunny day. You do not stare straight at the sun on a sunny day (with or without governmental advice), and similarly it will both hurt and damage your eyes to stare straight at the sun during the eclipse - except at totality, when the sun is less bright than the full moon.

These official warnings seem only to have increased confusion. Was the sun more dangerous than usual during an eclipse? Is it safe to go outside or to drive a car during the eclipse? In fact, the sun is no more dangerous than usual, and it is perfectly safe to look at the sun through approved filters. You could argue that it is far more responsible to offer grown adults a safe way to view the sun and the eclipse than warn against viewing it entirely.

In amongst all this, we seem to have lost sight of why anybody might want to see an eclipse in the first place. One reason is the beauty of it. As the eclipse approaches you see the shadow racing towards you. You see interference patterns projected on to buildings, giving the impression that the buildings are moving. At totality the sun's corona becomes visible, bright prominences or flares can be seen leaping out from around the moon's silhouette, and there falls a dramatic night-like silence as birds go to roost. Baily's beads (where light from the sun streams through highlighting the uneven surface of the moon) signal the end of the eclipse, followed by thE diamond ring effect. All of this seems to have become sidelined.

In addition to this, astronomers have been watching and studying the sun using eclipses for many years. It is primarily due to studies of the sun during eclipses in the nineteenth century that we know as much about the sun as we do. In the 1870s Norman Lockyer, for example, used a technique known as spectroscopy to determine the chemical composition of the sun's photosphere, corona and prominences - something which could only be done during an eclipse. Possibly the most famous eclipse experiment of all took place in 1919, when Arthur Eddington used apparent change in position of stars (due to the bending of light by gravitation) to prove Einstein's theory of general relativity. Though the experiment itself was controversial (another group doing the same experiment from a different location came up with different results) it did bring a certain legitimacy and interest to a theory which was later confirmed by eclipse observations.

Who would have thought that suggesting that it is safe to look through filters specially designed to protect eyes from the sun, and used without harmful effects by astronomers for the past 20 years, could be regarded as so controversial?

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