Expert: Jeffrey Eldred - 7/18/2009

Question
In some religions watrching sun during solar eclispse is considered a sin. To accentuate their claim the beleivers of those religions say that it's beacuse of the sin that whoever sees the sun during an eclipse gets blind. Please comment.
Please tell me whether sunrays anytime can make us blind or only sunrays emitted during the eclispse can make a person blind. Also please tell me differences between the normal sun and the sun in eclispse.

Answer
OVERVIEW:
There is a real danger from goes blind from staring at a partial eclipse, but it tends to get exaggerated a little. The rays from the sun are just the same as they always are though. We can explain what causes eclipses and what happens to the eyes during an eclipse with science and without a supernatural explanation.

RELIGION AND THE SKY:
While I didn't know that there was a religion that considered watching the solar eclipse to be a sin, I don't find it surprising. It is generally good advice not to look too much at an eclipse, because of the aforementioned risk to the eyes, and religions generally try to be compendiums of good advice given in God's name. Other religions would go as far as to say that whenever something bad happens to you and you don't understand how it relates to what you did, that a supernatural punishment for breaking an arbitrary rule is the only answer. Of course, this breaks down when you understand how the science of the thing works and this kind of supernatural thinking can have unfortunate consequences - like believing that people born disabled or poor have been cursed by God and fully deserve it. I would also add, that the fact that religions are able to give a simplistic warning about such things does not add any credence to the religion, since they found out about what an eclipse can do by looking at the sky and not by looking at a holy book.

There is actually a long history of various religions attaching special significance to mysterious cosmic phenomenon that have perfectly natural explanations today. Sun worship belongs to the world's oldest religions. The Black Stone in the Kaaba revered by Islam is very likely to be a meteorite, but the Saudi government has refused to have it tested. In Greek, Norse, and Aztec mythology lightning was thought to be summoned by a God. The Algonquin natives took the Aurora Borealis to be the spirits of their ancestors. Comets have been considered bad or good omens all over the ancient world. Now that we understand all these things scientifically, it seems silly to assign any more religious significance to these events than everyday occurrences.

BLINDNESS CAUSED BY AN ECLIPSE:
The danger of the sun is the same any time of the year, but because it doesn't hurt to look at the sun during the eclipse (and the blindness occurs a little later) that is when the problem of blinding yourself from the sun is most problematic. During an eclipse there is less visible light when you look at the sun, which is what our eyes can see and react to. Because there is less visible light everything appears dark, our retina doesn't protect itself by contracting like it usually does when exposed to a bright light and there is no discomfort that would cause someone to look away. But the sun also gives out invisible radiation in the form of infrared light and UV light which is actually what is most dangerous to the eyes. During an eclipse there is still less invisible UV and infrared light that reaches your eyes from the sun, but it still damages the eyes when you look long enough.

It might seem odd to you that the eyes evolved to protect itself from visible light when invisible light is the greater danger. But for all times and places except when an eclipse occurs, this defense mechanism works in protecting us from the sun. Also the main evolutionary reason the eye controls the amount of light that enters it in the first place is so that it can tell brighter areas from darker areas (required to make out shapes) but doesn't have to worry about whether the average amount of light is high or low (as it is during day and night respectively). While it isn't the best idea to stare at man-made lightning or bright fires either, they have much more visible light compared to how much UV and infrared light they have so they don't pose the same threat. Of course you can still be blinded by the special lasers in optical physics laboratories, burning a lot of magnesium, or by watching a nuclear bomb test from a distance, but you never hear as much about those because precautions are usually taken.

OTHER THOUGHTS:
This article gives another pretty good explanation of what happens during an eclipse and what the dangers are associated with it:
http://discovermagazine.com/1994/may/burningringoffir377

The sun does actually have variations in the nature and intensity of its rays, but they have nothing to do with eclipses. "Solar variation", "Solar cycle", and "sunspots" are good terms to search for more further information. Our detection of these solar cycles has occurred through modern scientific means and there is an actively improving theoretical understanding of the causes behind this cycle. Still it is quite interesting because this appears to have a significant impact on the climate and there is still we don't know about it. As a side note, no particularly dramatic solar activity is predicted to occur during the year 2012 and every doomsday scenario I've heard relating to that year is scientifically groundless.

Solar eclipses are rare and according to all accounts, beautiful. If you ever get the opportunity to see one (with eye protection), take advantage of it.