SAFE ECLIPSE VIEWING
We’ll start…and end…with this advice: NEVER LOOK AT THE UNECLIPSED SUN with just your eyes.
Your eye is like a small magnifying glass, focusing light on the back of the eye. Focusing direct sunlight on the retina will damage it, often permanently. There are no pain receptors in the retina, so damage can occur that you will not feel or possibly notice until hours later. Do not sunburn your eye! Your skin can peel; your eye cannot. So never ever look at the uneclipsed Sun without a proper filter between you and the Sun.
TO LOOK DIRECTLY AT THE SUN SAFELY:
Approved Solar Glasses
A range of companies offer solar eclipse glasses which have a filter to protect your eyes. Good solar eclipse glasses filter out all of the harmful ultraviolet and infrared light and almost all of the intense visible light to allow you to view the eclipse safely.
They are available from Rainbow Symphony and American Paper Optics in bulk. Many eclipse websites are selling them singly as well. Get a bunch for you, your family and friends! You’ll want spares in case a pair is damaged. Inspect them each and every time you use them. Visually check for holes, look at a wall to make sure you don’t see any light coming through before you look at the Sun.
DO NOT use these items for safe viewing:
DO NOT use a “Sun filter” that screws into a telescope eyepiece. At the eyepiece, sunlight is being focused and is very hot! These filters can and do fail catastrophically. Cracked open, your unprotected eye is now at the focus and will be damaged.
DO NOT use smoked glass. Not dark enough!
DO NOT use camera filters such neutral density.
DO NOT use black trash bags. Not dark enough!
DO NOT use exposed film, regular or x-ray. Not dark enough!
Do not make layers of this.
(even if you can find film)
DO NOT use dark sunglasses! No matter how cool looking they are. Not several pairs at once. Not safety glasses.
In short, nothing that can be found around the house is good for direct viewing of the Sun.
See more safe viewing techniques at: eclipse2017.nasa.gov/safety.