It's never a good idea to look directly at the sun, but the effects on the eyes are even more damaging when part of the sun is blocked by the moon's shadow. It makes the part still visible even brighter.
There are special glasses that will filter out those harmful rays and, if the pre-eclipse excitement is any indication, those glasses and viewers are in high demand.
Scammers likely to cash in
So isn't it logical that scammers and other less-than-forthright individuals will try to make a quick buck by selling counterfeit solar eclipse-viewing glasses? You can pretty much bet on it.
For that reason, you need to be very careful when you purchase solar glasses, to make sure they are certified. Buying a counterfeit will not only result in getting ripped off, you could also damage your eyesight.
The American Optometric Association (AOA) says people within the 70-mile wide path of the total eclipse will be able to view the two-plus minutes of the total eclipse -- when the moon completely covers the sun -- without eye protection, but during the partial covering certified eye protection is necessary.
The AOA says anyone looking at the partially-eclipsed sun will require special-purpose solar filters or other ISO-certified filters, such as glasses or hand-held viewer.
List of reputable vendors
The American Astronomical Society has provided this list of reputable vendors.
How do you tell if glasses or viewers are the real thing? According to NASA, The glasses and viewers should have certification information with a designated ISO 12312-2 international standard. They should also have the manufacturer’s name and address printed somewhere on the product.
If they don't have this information, chances are they are counterfeit. You can expect to see these counterfeit products show up in internet ads and in spam emails.
NASA says even certified products should not be used if they are more than three years old or have scratched or wrinkled lenses. Homemade filters and ordinary sunglasses should not be used to view a solar eclipse.