Safe eclipse viewing - important updated guidance on safety-certified viewers and the flood of Chinese copies


Hank Riley
 


Vastly shortened text included below.  I'd urge all people who intend to view the eclipse
to read the whole article from the American Astronomical Society at the link immediately
below.

The AAS site is also an excellent resource for all kinds of authoritative eclipse
information including indirect methods of viewing the eclipse with and without the use
of a telescope.





How to Tell If Your Eclipse Glasses or Handheld Solar Viewers Are Safe

Eclipse Glasses and Viewers

Short Answer

We used to say that you should look for evidence that they comply with the ISO 12312-2 international safety standard for filters for direct viewing of the Sun. But now the marketplace is being flooded by counterfeit eclipse glasses that are labeled as if they're ISO-compliant when in fact they are not. So now we suggest that you make sure you get (or got) your eclipse viewers from one of the suppliers listed on our Reputable Vendors of Solar Filters & Viewers page.

What to Avoid

Ordinary sunglasses (or multiple pairs of sunglasses), neutral density or polarizing filters (such as those made for camera lenses), smoked glass, photographic or X-ray film (unexposed, exposed, or developed), "space blankets," potato-chip bags, DVDs, and any other materials you may have heard about for solar viewing are not safe. In some cases these homemade filters may seem like they dim the Sun to a comfortable level, but that doesn't mean they do so across the whole electromagnetic spectrum. While you're enjoying a "comfortable" view of the "dim" Sun, solar infrared radiation could be cooking your retinas. And you wouldn't know till later, because your retinas don't have pain receptors. Only after the eclipse, when you notice blind spots or other vision problems, would you realize you'd made a catastrophic mistake.

What about welding filters? The only ones that are safe for direct viewing of the Sun with your eyes are those of Shade 12 or higher. These are much darker than the filters used for most kinds of welding. If you have an old welder's helmet around the house and are thinking of using it to view the Sun, make sure you know the filter's shade number. If it's less than 12 (and it probably is), don't even think about using it to look at the Sun. Many people find the Sun too bright even in a Shade 12 filter, and some find the Sun too dim in a Shade 14 filter — but Shade 13 filters are uncommon and can be hard to find. Our Reputable Vendors of Solar Filters & Viewers page doesn't list any suppliers of welder's filters, only suppliers of special-purpose filters made for viewing the Sun.

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