A solar eclipse occurs when the Moon passes directly between the Sun and Earth, casting a shadow on our planet. This celestial alignment offers a striking visual phenomenon. However, observing the Sun directly, even when partially obscured during an eclipse, can cause severe and permanent eye damage. This risk extends to all phases of a solar eclipse, except for the brief period of totality during a total solar eclipse.
The Hazards of Unprotected Viewing
Looking directly at the Sun during an eclipse, even for a short time, poses a significant risk to eye health. The intense light and radiation from the Sun can cause a condition known as solar retinopathy. This damage occurs when the Sun’s powerful rays reach the fovea centralis, a sensitive area in the retina responsible for sharp, detailed vision.
Unlike other eye injuries, solar retinopathy often occurs without immediate pain. Light exposure damages photoreceptors, leading to symptoms like blurry vision, distorted vision, blind spots, or altered color perception. These effects can manifest hours to days after exposure and, in some cases, result in permanent vision loss. Regular sunglasses offer no protection against this type of damage because they do not block the harmful UV and infrared radiation that can injure the retina.
Safe Indirect Observation Methods
Observing a solar eclipse safely without specialized direct-viewing eclipse glasses primarily involves indirect projection methods. These techniques allow viewers to see an image of the eclipsed Sun without looking directly at it. Two common and effective methods are using a pinhole projector or employing binoculars or a telescope for projection.
A simple pinhole projector uses two pieces of stiff white cardboard or paper. Make a small hole in one piece with a pin or thumbtack. With your back to the Sun, hold this cardboard up, allowing sunlight to pass through onto the second piece, which acts as a screen. The farther away the screen is held, the larger the projected image of the Sun will appear. This method safely projects a small, inverted image of the Sun, and common items like colanders or interlaced fingers can also create multiple pinhole projections.
Another indirect method involves using binoculars or a small telescope to project an image of the Sun. This technique requires a tripod to hold the optical device steady. One of the binocular lenses should be covered, and the binoculars should be pointed towards the Sun without looking through them. A white surface, such as a piece of cardboard, is then held a foot or more behind the eyepiece to catch the projected image of the Sun. This method can produce a larger and sharper image than a pinhole projector, but never look directly through the binoculars or telescope at the Sun, as this will cause severe eye injury.
Debunking Unsafe Viewing Practices
Many common items people might consider using for eclipse viewing do not provide adequate protection and are dangerous. Regular sunglasses, regardless of darkness or stacking, are ineffective and do not block harmful radiation. The light from the Sun, even when partially obscured, is still intensely bright and can cause harm.
Other materials like smoked glass, CDs, DVDs, or photographic film also fail to filter out the Sun’s harmful rays sufficiently. Using these can give a false sense of security while still allowing damaging radiation to reach the eyes. While some welder’s glass (Shade 12 or 14) can filter enough light, many readily available shades are insufficient or of uncertain authenticity. Looking at the Sun through unfiltered camera lenses, binoculars, or telescopes, even while wearing eclipse glasses, is dangerous, as these devices concentrate the Sun’s rays and can cause severe eye injury. Only certified solar filters that meet the ISO 12312-2 international safety standard should be used for direct viewing with optical devices or as standalone eclipse glasses.
Naked-Eye Viewing During Totality
There is one specific and rare exception where direct naked-eye viewing of a solar eclipse is considered safe: during the brief period of totality of a total solar eclipse. Totality occurs when the Moon completely blocks the Sun’s bright face, revealing its outer atmosphere, the corona. This moment lasts only a few minutes, depending on the observer’s location within the narrow path of totality.
This exception applies only to total solar eclipses and only when the Sun is fully obscured. During any partial phase of a total eclipse, or throughout the entirety of an annular eclipse where the Moon does not completely cover the Sun, direct viewing without proper eye protection is never safe. As soon as the Sun begins to reappear after totality, even as a tiny sliver of light, eye protection must be immediately put back on, or indirect viewing methods should be resumed. Failure to do so can result in severe eye damage.