— -- Experts are urging Americans watching the Aug. 21 total solar eclipse to buy smart when purchasing the necessary protective eyewear.
With counterfeit eclipse glasses hitting the market, NASA and the American Astronomical Society (AAS) suggest that consumers purchase off their long list of verified products to ensure safe viewing.
Retired NASA astrophysicist and photographer Fred Espenak told ABC News that he has heard rumors of counterfeit glasses being sold online.
It is unclear if there are counterfeit glasses also being sold in stores or by street vendors.
"The only way you can be sure that they're not fake glasses is to buy them from a reliable source," Espenak said.
Espenak recommends that people stick to the AAS's approved list of companies that manufacture and/or sell eclipse glasses and handheld solar viewers, which have been verified by an accredited testing laboratory to meet the ISO 12312-2 international safety standard.
"They've been put through a testing procedure to demonstrate that they're dark enough to prevent visible as well as ultraviolet and infrared light from passing through it," Espenak said. "They've gone through various laboratory testing in order to be certified for ISO testing. Filters have to be validated by the same standard."
Unfortunately, some companies are placing an ISO label on their counterfeit glasses, which is why following the list of manufacturers is a surefire way to know you're being safe, according to the AAS.
American Paper Optics is one of the manufacturers listed among those that meets the ISO standard on the AAS website.
Jason Mitchell is a partner at GSM Sales, which sells Soluna-brand glasses on Amazon. The glasses are manufactured by American Paper Optics.
Mitchell told ABC News that the Soluna brand faced issues in July with some Amazon sellers copying its design and claiming to have certified glasses produced by American Paper Optics. Mitchell explained that this is not possible considering the fact that Soluna glasses are exclusively manufactured for GSM Sales.
"Amazon has now done a great job eliminating all other sellers that claimed to be selling legitimate Soluna glasses, so there are no longer any issues with the validity of the Soluna glasses on Amazon," Mitchell said.
"We are only selling the glasses on Amazon, so we cannot guarantee the validity of Soluna glasses purchased through any other site," he added. "The only way that valid Soluna glasses could be sold through another site is if they were first purchased from GSM Sales on Amazon. To guarantee the authenticity of the Soluna glasses, they must be purchased from GSM Sales on Amazon."
Amazon released a statement to ABC News in regards to glasses being sold on their site, "We require sellers to comply with all our policies, including their responsibility to source and sell only safe, authentic products. Eclipse glasses sold on Amazon.com are required to comply with the relevant ISO standard.”
Besides American Paper Optics, who makes Soluna glasses, here is a current list of other approved companies that manufacturer and/or sell glasses through vendors and retailers, according to the AAS.
The AAS says on its website that just because they do not list a supplier, that does not indicate that "their products are unsafe," but rather that the AAS does not yet have the knowledge of that particular seller or that they have not verified the brand is safe.
"You can't assume that they're not safe because they're not on the list ... this list is growing," Espenak said.
Espenak said that there isn't any way to tell for certain if a set of eclipse glasses are counterfeit, but one indictor is if you are able to see something in the glasses other than the sun, which is why for now, the AAS suggests sticking to the current list of manufacturers when buying glasses.
The consequence of wearing glasses that aren't specially made to deal with the visible light from a solar eclipse and invisible radiation could be "serious eye injury, perhaps even blindness," according to the AAS, which also noted that special-purpose solar filters are many thousands of times darker than ordinary sunglasses.
Over 6,800 libraries across the country are distributing safety-certified glasses for the Aug. 21 eclipse, with many collaborating with scientists to hold viewing events and activities before and during the event. For a list of participating libraries distributing glasses from AAS’s approved list, click here.
Quick tips for buying safety glasses, according to the AAS and Espenak:
ABC News' Morgan Winsor contributed to this report.