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by ggonnigan on March 13th, 2006

ggonnigan

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How does looking directly at a solar eclipse damage your eyes?

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  • by Alatea on March 13th, 2006

    Alatea

    Observing the Sun can be dangerous if you do not take the proper precautions. The solar radiation that reaches the surface of Earth ranges from ultraviolet (UV) radiation at wavelengths longer than 290 nm to radio waves in the meter range. The tissues in the eye transmit a substantial part of the radiation between 380 and 1400 nm to the light-sensitive retina at the back of the eye. While environmental exposure to UV radiation is known to contribute to the accelerated aging of the outer layers of the eye and the development of cataracts, the concern over improper viewing of the Sun during an eclipse is for the development of "eclipse blindness" or retinal burns.

    Exposure of the retina to intense visible light causes damage to its light-sensitive rod and cone cells. The light triggers a series of complex chemical reactions within the cells which damages their ability to respond to a visual stimulus, and in extreme cases, can destroy them. The result is a loss of visual function which may be either temporary or permanent, depending on the severity of the damage. When a person looks repeatedly or for a long time at the Sun without proper protection for the eyes, this photochemical retinal damage may be accompanied by a thermal injury - the high level of visible and near-infrared radiation causes heating that literally cooks the exposed tissue. This thermal injury or photocoagulation destroys the rods and cones, creating a small blind area. The danger to vision is significant because photic retinal injuries occur without any feeling of pain (there are no pain receptors in the retina), and the visual effects do not occur for at least several hours after the damage is done.

    The only time that the Sun can be viewed safely with the naked eye is during a total eclipse, when the Moon completely covers the disk of the Sun. It is never safe to look at a partial or annular eclipse, or the partial phases of a total solar eclipse, without the proper equipment and techniques. Even when 99% of the Sun's surface (the photosphere) is obscured during the partial phases of a solar eclipse, the remaining crescent Sun is still intense enough to cause a retinal burn, even though illumination levels are comparable to twilight.

    Failure to use proper observing methods may result in permanent eye damage or severe visual loss. This can have important adverse effects on career choices and earning potential, since it has been shown that most individuals who sustain eclipse-related eye injuries are children and young adults.

    The same techniques for observing the Sun outside of eclipses are used to view and photograph annular solar eclipses and the partly eclipsed Sun. The safest and most inexpensive method is by projection. A pinhole or small opening is used to form an image of the Sun on a screen placed about a meter behind the opening. Multiple openings in perfboard, in a loosely woven straw hat, or even between interlaced fingers can be used to cast a pattern of solar images on a screen. A similar effect is seen on the ground below a broad-leafed tree: the many "pinholes" formed by overlapping leaves creates hundreds of crescent-shaped images. Binoculars or a small telescope mounted on a tripod can also be used to project a magnified image of the Sun onto a white card. All of these methods can be used to provide a safe view of the partial phases of an eclipse to a group of observers, but care must be taken to ensure that no one looks through the device. The main advantage of the projection methods is that nobody is looking directly at the Sun. The disadvantage of the pinhole method is that the screen must be placed at least a meter behind the opening to get a solar image that is large enough to see easily.

    The Sun can only be viewed directly when filters specially designed to protect the eyes are used. Most such filters have a thin layer of chromium alloy or aluminum deposited on their surfaces that attenuates both visible and near-infrared radiation. A safe solar filter should transmit less than 0.003% (density~4.5) of visible light (380 to 780 nm) and no more than 0.5% (density~2.3) of the near-infrared radiation (780 to 1400) shows the spectral response for a selection of safe solar filters.

    B. Ralph Chou, MSc, OD
    Associate Professor, School of Optometry, University of Waterloo
    Adapted from NASA RP 1383 Total Solar Eclipse of 1999 August 11, April 1997, p. 19.
    More on this link.
    http://sunearth.gsfc.nasa.gov/eclipse/SEhelp/safety2.html

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  • by notmrjohn on March 21st, 2006

    notmrjohn

    Ala's answer is, as usual, excellent. I would just add a bit of info concerning that retinal burning, why it happens so fast, and why it is so likely to occur.( And its not just during an eclipse that one should not look directly at the sun, one should NEVER do so.) Most of us have probably used a magnifying glass to concentrate the light of the sun to at least burn a hole in a piece of paper, if not to start an actual fire. ( I am sure us baggers were intellectually above average as kids and never used a glass to 'pop' ants.) That little hot spot of light is a perfectly projected and concentrated image of the sun. The lens in our eye acts just like that magnifying glass and projects a concentrated image onto our retina, and just as fast as the glass chars the paper, our lens chars our retina. Incidentally, you shouldn't look directly at that glass projected image either, as it is concentrated and can also damage your retina.
    That pinhole in a card acts just like the magnifying glass and focuses the image, and is just as damaging. I'm kinda s'prized the good Dr. Chou didn't mention that, him bein' a OD and all, I'm even more wary of his mentioning telescopes and binoculars as a projector, it is easier to adjust the focus on the screen but the image is concentrated and despite his caveat, I just know some idjit is gonna walk up and look thru the telescope and get a triple concentrated instantaneous eye fry, with binoculars it will be in both eyes. It is better to use a larger hole, about the size of a round pencil, or a regular ol' hole punch for a nice clean edged hole, or use a piece of that 'perfboard' (pegboard). The larger hole requires a longer distance to the 'screen' than a pinhole, but the circle is not so concentrated, it is safer too if the screen is not white but gray or some other dull color, a piece of corrugated cardboard box works fine. It is easier to fasten the 'holy board' to something and just hold a small screen and move it to focus.
    My biggest disappointment was in learning that I was not the discoverer of the easiest way to see an eclipse. Away back when I experienced my first eclipse, I was around 10 or so, I grew frustrated at trying to focus my pinhole-in-an-index card and was about to give up when I glanced under the trees, there they were, thousands of perfectly focused images. As usual ever time I come up with a brilliant idea I discover somebody else already had it. (Or sumbudy really is scanning my brain waves.) BTW Stinkbugs are slower than ants and have a harder time evading the death ray, they also make a satisfyingly larger and odiferant pop.

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  • by Ron C on May 5th, 2009

    Ron C

    You don't look directly at a solar eclipse for the same reason you don't look directly at the sun or any bright object. It can damage you optic nerves and retina. You overload the system and literally give your eyes sunburn. Continued exposure to ultra bright light can also cause cataracts. That's welders use shield.

    People that don't protect their eyes end up trading sunglasses for white canes.

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  • by oliver007 on May 5th, 2009

    oliver007

    Yes, you should look through a filter.

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  • by john pennington on May 5th, 2009

    john pennington

    You slaughtered that word.

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  • by Countess Crapula on May 5th, 2009

    Countess Crapula

    A solar ECLIPSE can be looked at directly once it's covered; just don't stare and keep looking because it can do the same damage as staring into the sun. I believe it's not good when the sun is about to be covered and that bright light of the sun is being refracted around the moon; it has to do with the angle, I think.

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  • by FaerieWhings on February 6th, 2008

    FaerieWhings

    I got comped a bottle of champagne and grey goose.

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  • by Carmel_F on June 15th, 2011

    Carmel_F

    i looked at the luner eclipse this morning, with my naked eyes and now my eyes hurt. Have i caused some damage.

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  • by FaerieWhings on February 6th, 2008

    FaerieWhings

    Check out this google I did. They sell glasses to block out the damaging rays.

    http://www.google.com/search?q=eclipse+glasses&rls=com.microsoft:*:IE-Address&ie=UTF-8&oe=UTF-8&sourceid=ie7&rlz=1I7GGLR

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  • by LadyDutchess on February 6th, 2008

    LadyDutchess

    That is so cool, i love shopping too. And its your birthday, mines comming up, how old if you dont mind me asking and wat are you going to do????? :-)

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  • by Grammy Robin on February 6th, 2008

    Grammy Robin

    Like Faeriewhings said, you can buy special glasses to view and eclipse. A welding mask will work as well.

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  • by Juliaa_P on January 13th, 2011

    Juliaa_P

    LOOKING AT THE SUN CAN DAMAGE YOUR EYES ? YOU THINK WHEN THE SUN IS 10 TIMES BRIGHTER IS SAFER ? NOOO . ?

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More Questions. Additional questions in this category.

You're reading How does looking directly at a solar eclipse damage your eyes? - which can also be phrased in the following ways:

  • Could someone explain to me how i could view a partial eclipse of the sun without doing any permenant damage to my eye?
  • Why is it bad to look at a solar ecaleps with your eyes?

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