Why Can’t You Look Directly at the Sun During a Solar Eclipse?
It’s never a good idea to stare directly at the sun. If you’ve ever looked directly at the sun, you’ve probably looked away very quickly when your eyes began to hurt. The ultraviolet light from the sun is quite powerful. If you’ve ever experienced bad sunburn, you know what sunlight can do to your skin in just a short time if left unprotected.
Your skin is much tougher than your eyes, and the delicate parts of your eyes can be damaged by the sun much more quickly. That’s why it’s a natural reaction to divert your eyes in bright sunlight. So why is it even more dangerous to look at the sun during an eclipse?
As the Sun darkens during an eclipse, your eyes think it’s getting dark. Therefore, your pupils dilate to let in more light just like they do every evening. Since it’s getting darker out, your eyes’ natural protective defenses, such as pupil contraction and blinking, also don’t kick in.
However, during an eclipse — except at the moment of totality when the sun’s disk is completely covered by the moon — there is still sunlight entering your eyes. This sunlight can flood your retinas, over stimulating the rods and cones that sense light and causing them to release chemicals that can damage the retinas. This condition is known as solar retinopathy, and it can cause permanent eye damage. Since there are no pain receptors in the retina, you won’t know it’s happening until it’s too late. Although permanent blindness is rare, serious eye damage can occur that has lasting effects.
If you can’t look at the sun during a solar eclipse then, are you just out of luck? Not necessarily! With a little preparation, you can take steps to view a solar eclipse safely. According to NASA, the safest way to view a solar eclipse is through special sun filters that block out the harmful ultraviolet radiation. You can find glasses with these filters online or at specialty stores.
Under normal conditions, the Sun is so bright that it is difficult to stare at it directly. However, during an eclipse, with so much of the Sun covered, it is easier and more tempting to stare at it. Looking at the Sun during an eclipse is as dangerous as looking at it outside an eclipse, except during the brief period of totality, when the Sun’s disk is completely covered (totality occurs only during a total eclipse and only very briefly; it does not occur during a partial or annular eclipse).
Viewing the Sun’s disk through any kind of optical aid (binoculars, a telescope, or even an optical camera viewfinder) is extremely hazardous and can cause irreversible eye damage within a fraction of a second.
Viewing the Sun during partial and annular eclipses (and during total eclipses outside the brief period of totality) requires special eye protection or indirect viewing methods if eye damage is to be avoided. The Sun’s disk can be viewed using appropriate filtration to block the harmful part of the Sun’s radiation.
Sunglasses do not make viewing the Sun safe. Only properly designed and certified solar filters should be used for direct viewing of the Sun’s disk. Especially, self-made filters using common objects such as a floppy disk removed from its case, a Compact Disc, a black color slide film, smoked glass, etc. must be avoided.
The safest way to view the Sun’s disk is by indirect projection. This can be done by projecting an image of the disk onto a white piece of paper or card using a pair of binoculars (with one of the lenses covered), a telescope, or another piece of cardboard with a small hole in it (about 1 mm diameter), often called a pinhole camera. The projected image of the Sun can then be safely viewed; this technique can be used to observe sunspots, as well as eclipses.
Care must be taken, however, to ensure that no one looks through the projector (telescope, pinhole, etc.) directly. Viewing the Sun’s disk on a video display screen (provided by a video camera or digital camera) is safe, although the camera itself may be damaged by direct exposure to the Sun.
The optical viewfinders provided with some video and digital cameras are not safe. Securely mounting #14 welder’s glass in front of the lens and viewfinder protects the equipment and makes viewing possible. Professional workmanship is essential because of the dire consequences any gaps or detaching mountings will have.
In the partial eclipse path, one will not be able to see the corona or nearly complete darkening of the sky, however, depending on how much of the Sun’s disk is obscured, some darkening may be noticeable. If three-quarters or more of the sun is obscured, then an effect can be observed by which the daylight appears to be dim, as if the sky were overcast, yet objects still cast sharp shadows.