Shade #13 is a good compromise but is not as widely available as shades #12 and #14. Shade #12 is also safe, but many people find the Sun uncomfortably bright when using this filter. Welder’s glass/filters provide excellent quality for visual observation, and shade #14 is perfectly safe. So what can be used to view solar eclipses? One widely available filter that is safe for solar eclipse viewing is a shade number 14 welder’s glass (also available in plastic), which can be obtained from welding supply outlets. Just because the Sun appears dim doesn’t mean the filter is safe, so do not use any homemade filters. All will dim the Sun to some degree but not nearly enough to protect your eyes. Never look using CDs, CD-ROMs, DVDs, color and black-and-white film, film negatives with images on them, sunglasses (single or multiple pairs, polarized or not), photographic neutral density filters, or polarizing filters. Unfortunately, there is an almost limitless variety of handy materials that will dim the Sun significantly but are nevertheless unsafe and dangerous. If you feel you need to look directly at the Sun to follow the partial eclipse, you must shield your eyes using a safe, special-purpose solar filter. Here are three links to help you make such a projector: Using a cereal box (NASA) using a larger box (George Eastman Museum) and a website with instructions and photos. The downside is that only one person at a time can see the projected image. Another advantage is that you have your back to the Sun, so there’s no temptation to peek directly at the eclipse. The idea is to project the solar disk onto the inside of a mostly closed box so there is less ambient light surrounding the image, making it easier to see. With just a little work, you can make a superior pinhole projector using a box. (Do not look at the Sun through the pinhole!) The problem with this example, and others like it, is that the image is usually dim and washed out by the ambient daylight it’s a very disappointing sight. A typical instruction might be this: Pass sunlight through a small hole punched in an index card, and project an image of the Sun through it onto a nearby white surface. There are lots of how-to examples on the Internet.
Speaking of pinhole projection, that’s another way to look at the solar eclipse safely. During the partial eclipse, the tiny spaces between the leaves will act as pinhole projectors, dappling the ground with images of the crescent Sun! If your observing site has leafy trees, look at the shadows of leaves on the ground.
The little spaces between your fingers will project a grid of small images, showing the Sun as a crescent. Stand with your back to the Sun and look at the shadow of your hands on the ground. Cross the outstretched, slightly open fingers of one hand over the outstretched, slightly open fingers of the other. Amazingly, the little holes project solar crescents onto the ground. If you’re observing from home, head to your kitchen, bring out a colander or slotted spoon, and hold it over white paper or pale concrete. And the safest way to view the partial phases of a solar eclipse is to not look directly at the Sun at all. To follow the progress of a solar eclipse, it must be safety first. Even worse, the visual effects are typically not noticeable until hours after the damage is done. While all this is taking place within your eye, you won’t feel a thing, because there are no pain receptors in the retina. The consequence is a loss of vision that may be either temporary or permanent, depending on the severity of the damage.
The high level of radiation causes heating that literally cooks the eye and destroys the rods and cones. This retinal damage may be accompanied by a thermal injury. Even a brief exposure of the eye’s retina (the thin layer of tissue lining the back of the eye) to the Sun’s intense light will result in damage to the eye’s light-sensitive rod and cone cells. Improper solar eclipse viewing can result in what’s known as eclipse blindness.