Organizers helping people get ready to take in the Aug. 21 solar eclipse are expressing a new worry – counterfeit eclipse glasses.

The glasses – specially treated plastic lenses usually with light cardboard frames – will be needed to look at the partial phases of the eclipse.

The experts are emphatic: Don’t look at the sun with a naked eye, and don’t look with sunglasses.

“Never, never, never stare directly at the sun,” Elizabeth Brown of the Astronomical Society of Kansas City eclipse committee said during an eclipse presentation this week.

Eclipse glasses have been available for a dollar or two at many locations but appear to be running in short supply. Now counterfeit glasses have been showing up in places such as Amazon.com, so the American Astronomical Society has updated its guidelines.

It had urged people to buy glasses stamped with an ISO code – 12312-2 – meaning those glasses meet international standards. But now the AAS says unscrupulous manufacturers have been stamping that number on their products too. It cites “the many reports we’re getting about unsafe eclipse glasses flooding the marketplace.”

So the AAS’s new guidance is to use vendors it considers reputable. Those are:

• American Paper Optics.

• APM Telescopes.

• Baeder Planetarium.

• Calestron.

• DayStar.

• Explore Scientific.

• Lunt Solar Systems.

• Meade Instruments.

• Rainbow Symphony.

• Thousand Oaks Optical.

• TSE 17.

Brown urged checking glasses you might have bought recently.

“Find out, because we don’t want you damaging your eyes in any way,” she said.

The eclipse will cover all of North America, but only a roughly 70-mile corridor across 14 states, including Missouri, will get a brief but intense total eclipse. For instance, on the Independence Square, the partial eclipse starts at 11:41 a.m. The total eclipse starts 39 seconds after 1:08 p.m. and lasts one minute and 10 seconds. Then the partial eclipse ends at 2:36 p.m.

Millions are expected to make a party of it, gathering to watch as the moon slowly covers the sun and the skies grow darker. That’s also the time of concern about eye safety: Only during the brief full eclipse can people look at the sun. During the partial eclipse phases – or any other time – eclipse glasses are needed.

In addition to the expected hassles and hazards as large numbers of people head to places such as St. Joseph, where the total eclipse is almost two minutes, 40 seconds, officials are stressing eye safety.

The AAS says to inspect your eclipse glasses or other solar filters to make they aren’t scratched, torn, punctured or otherwise damaged. If they are, toss them. If you wear glasses, keep them on and wear the eclipse glasses over them.

Don’t look at the sun, even partially eclipsed, through an unfiltered camera, telescope, binoculars or other optical device. Don’t use binoculars, cameras, telescopes and similar devices along with eclipse glasses. The concentration of solar rays can damage the filter and then damage your eyes.

Also, keep a close eye on the kids and make sure they are wearing eclipse glasses or using other filters.

It’s human nature that people will want to snap a few photos, but eclipses are tricky, and some experts suggest just enjoying the show and leaving photography and special lenses to the professionals. The total eclipse is brief, and Brown said it’s no time to be fumbling with a camera. Your own eyes, she said, will see things a camera will not.

“Basically, I just try to tell people just enjoy it,” she said.