Astronomy Blog

Don't Look At The Sun - part 2

Eclipses and transits of the Sun are amazing celestial events. They can be awe-inspiring and beautiful and enthuse people to travel the world to experience them. At the same time they can be dangerous. The Sun is a ball of gas about 330,000 times more massive than the Earth with a core undergoing nuclear fusion reactions. As a result, and given that we are only 149 million kilometres from it, the Sun is very bright. Astronomers always warn that these events should be viewed with safe solar viewing equipment so that you don't damage your eyes.

Back in 2004, in the weeks leading up to the transit of Venus, Megan and I filmed the result of focussing light from a small telescope onto a grape. Whilst far from a perfect analogy for the human eye, the sound of sizzling grape and the burnt patch on it were enough to remind me of why it is a bad idea! Yesterday, I received a comment on that post from Matthew who had been told about the "benefits of looking directly at the morning (rising) sun". He asked me if it was good to look at the Sun. The simple answer is no.

Human eyes are extremely sensitive optical instruments that can deal with a huge range of conditions. Some have even been known to detect just a few photons of light in the dark. That is a very impressive level of sensitivity. However, increasing the light levels considerably above ambient amounts starts to cause damage.

One of the classic things for a child with a magnifying glass to do is to burn an ant (in the interests of ant safety I don't recommend this). The ant burns because the sunlight is focussed from a large area (that of the magnifying glass) down into a small point making the light more intense. By staring directly at the Sun you are effectively using your eye's lens as the magnifying glass and your retina as the ant. However, it isn't just the increase in temperature that causes damage to your eyes. For a start you'll be getting more UV and infra-red radiation into your eyes. Secondly, the very intense visible light - safe solar filters reduce the luminosity by more than 33,000 times - starts a series of complex chemical reactions which will stop the cells responding to visual stimulus and can destroy them. Killing off cells in your retina is not a good thing. What makes this more scary is that there are no pain receptors in your retina so you can't even feel the damage being done.

Matthew pointed me to a website that made me pretty concerned. The website is about Sunyogi Umasankar who, apparently, stares at the Sun for extended periods. I do not recommend this and am very sceptical about some of the claims. Interestingly, some of the initial visual effects described on that site sound fairly realistic for someone causing damage to their eyes. One claim, that the Sun started to appear as a "clear hazy ring with soft blue sky inside", sounds similar to an after image of staring at a red light and then at a white surface. The Sun, especially at sunrise and sunset, usually appears at the redder end of the spectrum because the long path of the light through the atmosphere tends to scatter out the blue light. I can imagine that staring at a red light source for extended times will de-sensitise the cells to red light whilst neighbouring cells (those seeing the blue sky) won't. The brain may very well interpret the information from the cells seeing the Sun as the complementary colour. However, I don't want to try this experiment myself. Another site describes a Japanese man's account of staring at the Sun. He says he saw 'auras' around family members after staring at the Sun. It's hard not to think of these as a combination of after images and possible long-term damage to his eyes.

Ultimately, you can choose what to do with your own eyes. There is no evidence that it benefits your health and indeed it is very likely to cause long-term damage to your vision. You can damage your vision if you want to but I prefer to enjoy the beautiful colours and sights of the universe around me with a pair of nice, healthy eyes.