NationalEclipse.com | Mar 13, 2017 | National Eclipse Blog
The most important thing to consider when planning for a solar eclipse isn't your location within the path of totality, your distance to the centerline, or even the weather. It's eye safety. If you attempt to view an eclipse incorrectly, there's a really great chance your souvenir of the eclipse will be irreparable eye damage or even blindness. We all want to make lifelong memories on August 21, but those memories should be indelibly imprinted onto our minds, not our retinas.
Unfortunately, the media sometimes neglects to mention the importance of solar eclipse eye safety and occasionally they even unwittingly provide incorrect or dangerous information. Recently, one of the largest media companies in the world suggested that people should use "sunglasses" to view the eclipse on August 21. Of course, ordinary sunglasses are never safe to use for eclipse viewing. Another media outlet encouraged readers to get their binoculars ready for the eclipse and never mentioned the fact that optical devices like cameras, binoculars, and telescopes need specially designed solar filters that fit snugly on the front end (the Sun side) of the device. Attempting to view an eclipse with an unfiltered optical device is like holding a magnifying glass to your eye while focusing direct sunlight through the lens. No, you definitely don't want to do that.
Our hope is that as we get closer to August 21, the media will take the subject of eye safety more seriously and communicate the proper and safe way to view a solar eclipse as carefully and unambiguously as possible. Too many eyes are at risk not to get this information right every single time. In the meantime, here's what you need to know to stay safe on August 21:
Use Eclipse Safety Glasses or Viewers
You must use special eclipse safety glasses or viewers to view a partial eclipse, an annular eclipse, and the partial phases of a total eclipse. (For the record, total eclipses are partial most of the time within the path of totality and partial all of the time outside the path of totality.) Although it may be tempting to look directly at an eclipse with unprotected eyes when so much of the Sun is obscured, the small amount of light emitted during even a 99.9 percent partial eclipse is still dangerous. The only time it's safe to look at a total eclipse without proper eye protection is during the very brief period of "totality" when the Sun is 100 percent blocked by the Moon. If you're not located within the narrow path of totality where the eclipse will become total for a very brief period of time, there is never a time when it's safe to look with unprotected eyes.
Be Wary of Phony Glasses
Make sure that your eclipse safety glasses or viewers are certified as meeting ISO standards for safe solar viewing. The current standard for safe solar viewing is ISO 12312-2; your eclipse glasses or viewers should have this designation printed on them. Take care to purchase your glasses or viewers directly from a legitimate manufacturer of certified safe solar viewers or a reputable seller who purchased directly from a legitimate manufacturer and be wary of products that claim to be safe but aren't. Be very careful and don't use any product unless claims of safety can be verified.
Update: For the 2017 eclipse, there were many reports of unsafe eclipse glasses being distributed as well as reports of counterfeit eclipse glasses printed with names of legitimate manufacturers, including many that were sold on Amazon. Leading up to the 2017 eclipse, the American Astronomical Society provided guidance on how to tell if your eclipse glasses or viewers are safe.
Before using your glasses or viewers, make sure that they aren't damaged in any way (lenses shouldn't have scratches or wrinkles) and that you read all of the safety instructions that came with them. Children should always be supervised by a responsible adult when using eclipse safety glasses or viewers.
Don't Improvise
Unless a product has been specifically designed for safe solar viewing and has been certified as meeting international standards for such products, it's best to assume that a device, method, or instrument is unsafe. Don't risk it! Items such as regular or polarized sunglasses, smoked glass, exposed film, medical x-rays, homemade filters, and many others are all unsafe. You can use welder's glass to view an eclipse, but it must be #14 welder's glass; any rating below #14 is not safe. It's also safe to view an eclipse using indirect methods, such as projecting an image of the eclipsed Sun onto a white screen. Search online for "pinhole projector" and follow the instructions provided by a trusted organization like NASA to make your own.
Protect Your Eyes Before and After Totality
A total solar eclipse will be "total" for a very short period of time and only in the narrow path of totality. If you're located in the path of totality, don't remove your eclipse glasses until the very last bit of the Sun is gone and you can no longer see any light through them. Again, it's only safe to look with unprotected eyes when the Sun is 100 percent blocked by the Moon and only the soft wisps of the solar corona are visible. Once totality begins, it's important to know precisely when totality will be ending in your exact location so that you can once again put on your eclipse glasses before the first brightness of the exposed Sun is revealed.
To determine the exact start time, end time, and duration of totality for any location, we recommend the interactive Google eclipse maps developed by Xavier Jubier. You should also allow for a very generous margin of error to ensure that you are no longer looking with unprotected eyes when totality ends (and keep in mind that your clock or watch may not be in sync with astronomical time!). Additionally, NASA advises that you should pay careful attention to the edge of the Moon opposite of where the Sun last appeared. When you start to notice a very slight crescent-shaped brightening, you'll know that totality is coming to an end. This is your signal to look away or put your eclipse glasses back on before the first flash of exposed sunlight. As mentioned earlier, children should always be supervised by an adult who fully and clearly understands safe eclipse viewing procedures.
Optical Devices Must Have Solar Filters
As already noted, attempting to view an eclipse using cameras, binoculars, telescopes, or other optical devices without proper solar filters is extremely hazardous and can permanently damage the eyes in an instant. These devices need specially designed solar filters that fit snugly on the front end (the Sun side) of the device. Never attempt to view an eclipse through an optical device using eclipse glasses or any type of filter that attaches to the viewing side (as opposed to the Sun side) of the instrument; the focused light will destroy the filter and enter and damage your eyes. Remember the magnifying glass analogy? Since viewing or photographing a solar eclipse with an optical device requires specialized equipment and knowledge, your best bet is to consult with a qualified astronomer or just enjoy the eclipse with your own eyes using the safe eclipse viewing procedures already mentioned.
For more information on how to safely view a solar eclipse, see the excellent pages on viewing safety by the American Astronomical Society and NASA.
