Beware! The market is being flooded with fake eclipse glasses which won't protect your eyes!
People are almost certainly going to go permanently blind as a result.
Here are some ways to check to see whether your eclipse glasses are the genuine article.
Your best bet, if you haven't bought your glasses yet, is to get them from trusted, reputable sources. Here is the AAS's list of approved, reputable vendors. You can trust glasses bought from any of them.
Here is a guide to the very best stuff. But remember how high the odds are. The damage done to your eyes by viewing the sun without adequate protection is permanent. Stories are told about a great scientist who supposedly viewed an eclipse with only one. unprotected eye and thereafter could see only reds and blues through it. If so, he got off lightly; that's a good way to go totally blind.
It will be safe to look at the sun ONLY during totality, and not an instant before or an instant afterward. If you do not live in the relatively narrow band of totality, you will see a partial eclipse. In that case, NEVER look directly at the sun.
Ordinary sunglasses will offer absolutely no protection. Welder's filters lighter than shades 12, 13 and 14 will probably not protect you, and smoked glass can't be counted on either. Pinhole projectors or even round holes- the holes in your belt, even- if held between the sun and the ground will project an image of the eclipse on the ground. Even making the "OK" sign with your fingers will do the trick, though the image will be distorted because the "hole" won't be perfectly round. But these are a poor substitute, especially given the awesome beauty and rarity of this event.
Remember, looking at the sun directly except during totality can be disastrous. Here and here are accounts of what has happened when people have tried to watch previous eclipses without proper protection.
I personally have waited all my life for this. Another total solar eclipse will be visible in the United States on April 8, 2024, in case you miss this one; otherwise. you'll have to wait until August 23. 2043, when one will be visible in Wyoming, North Dakota, and Minnesota. Yet another eclipse will be visible on a path beginning in Northern California and ending in Florida on August 12 of the very next year. After that, you'll have to wait for 2099.
Here are the paths future American total eclipses will take.
But for now- if you do watch this eclipse, be careful. It may very well be the sight of a lifetime, but not one worth losing your sight for the rest of your life.