On August 21, North America will experience the first total solar eclipse visible across the continent in nearly a century––and, while it may seem illogical, this period of semi-darkness is an important time to practice sun safety.
That’s because while during an eclipse, you won’t want to tear your eyes away from the show, staring directly at the sun can lead to solar retinopathy, a condition where light floods the eye’s retina. In 1999, 45 patients visited an eye clinic in Leicester, England, after viewing a solar eclipse without proper eyewear. About half of the patients suffered from eye pain; the others reported impaired vision. Although these eclipse watchers were not totally blinded, several incurred long-term damage.
The United States hasn’t experienced a total eclipse since 1979, and that one only passed over a small swath of the Northwest. This year, in contrast more than 500 million people in North America, plus parts of South America and northwestern Europe, will be able to see at least a partial eclipse. Those within a 70-mile wide path between Oregon and South Carolina will witness a total eclipse.
A partial eclipse occurs when the moon blocks part of the sun from view. A total eclipse, in contrast, is when the moon completely blocks the sun. “Totality,” the part of the total eclipse when the sun is completely covered, lasts only around two minutes.
Most people in the continental United States live within a one- to two-day drive of the total eclipse’s path. Madhulika Guhathakurta, the lead program scientist for NASA’s “Living With a Star” initiative, says the breadth of the path makes the eclipse accessible to everyone. She says observing a total eclipse is transformative: “It’s akin to the way astronauts describe their first trip to space. You’re just so in awe of nature.”
To view the solar eclipse, you’ll need proper equipment. It may seem odd to don protection in the semi-darkness of a partial eclipse, but staring at the sun can cause retinal injury. The only time it’s safe to look at the sun without protection is during totality. Keep your equipment on hand, and put it back on when the sun starts to reappear.
Opt for gear featuring ISO-approved solar filters, which are about 100,000 times darker than everyday sunglasses. The American Astronomical Society’s website includes a list of manufacturers that have certified their products meet the ISO 12312-2 standard. If you purchase equipment from other outlets, double check that their merchandise meets ISO standards.
Whether you’re a stargazing neophyte or dedicated astronomer, this gear will help you make the most of a spectacular event.
Eclipse glasses and handheld viewers
Eclipse glasses look like hybrids of 3-D movie glasses and sunglasses. As Guhathakurta explains, these glasses have the added protection of a solar filter. Whereas sunglasses only block UV rays, eclipse glasses also cut off visible light.
If you’re a casual observer or part of a large group, you’ll like these glasses’ low prices and bulk packaging. You can buy a pack of five paper glasses from Rainbow Symphony for around $12. If you want a sturdier option, try these plastic glasses from American Paper Optics. And feel free to go for style: TSE17 has a $5.05 stars-and-stripes five-pack, and American Paper Optics features everything from Bill Nye glasses to astronaut-themed frames.
Looking for something between basic glasses and high-tech binoculars? Check out this handheld viewer from Celestron. For $9.95, you’ll receive two viewers with 2x magnification capabilities and a pocket eclipse guide.
Binoculars and telescopes
Binoculars and telescopes are pricier than eclipse glasses and handheld viewers but can be worth the investment. They feature a higher magnification, but higher magnification results in a shakier image––as power increases, the equipment becomes more sensitive to its holder’s small hand movements.
Binoculars are rated with two numbers. The first number is the magnification, the second is the aperture—the diameter of the front lens, measured in millimeters. If you’re buying a pair of binoculars and plan to use them for other astronomy viewing, the bigger the aperture, the better, but bigger lenses also mean heavier equipment.
The following options offer a range of viewing strengths. Celestron’s EclipSmart binoculars feature non-removable solar filters, so you’ll only be able to use them for solar viewing. A 10×25 pair (10x magnification and 25mm aperture) costs around $35, while a 10×42 pair costs just about twice as much. A cheaper option is Lunt’s mini SUNocular. A 6×30 pair costs $29.95.
If you prefer binoculars with removable solar filters, Meade has a $69.99 10×50 pair that works for both solar viewing and nighttime stargazing. Once you remove the solar filters, the binoculars will operate like a normal pair.
Telescopes offer some of the best eclipse views, but you’ll pay more for added detail if you want an advanced model. A basic lightweight option is the Explore Scientific Sun Catcher 70mm telescope. It costs $59.99 and can be used during both the day and night. A more advanced option is the $99.95 Celestron EclipSmart telescope. It offers 18x magnification, 50mm aperture and non-removable solar filters.
Another choice is the Meade EclipseView telescope. The cheapest model is a $79.99 82mm reflecting telescope designed for on-the-go use. A sturdier long-term bet is the 76mm reflecting telescope, which costs $129.99. Both models feature removable solar filters and are suitable for solar and nighttime use.
Add-on solar filters
Another category of eclipse viewing gear is add-on filters. These can be attached to binoculars, telescopes and cameras not originally designed for solar viewing and are mainly used by experienced observers. Similarly to eclipse-specific gear, add-on filters prevent retinal damage. They also protect your equipment’s optics from the heat of the sun, as the intensity of an eclipse can damage gear designed for nighttime observing.
Filters are typically made of metal on glass (sturdy but most expensive), aluminized polyester film (also known as Mylar) or black polymer (also used in eclipse glasses). Rainbow Symphony sells black polymer and silver Mylar filters starting at $19.95. Thousand Oaks Optical and Orion offer higher-end filters ranging in price from $22 to $150-plus.
If you want to view the eclipse without spending money on special equipment, you’re in luck. Stand with your back to the sun, and use your hands, a hole-punched index card or even a patch of leaves to create a tiny opening. As sunlight flows through the empty space, an image of the sun will project onto a nearby surface. For more detailed instructions, visit the American Astronomical Society’s pinhole projection page.
Guhathakurta’s final words of advice are simple: During the partial eclipse, “do not look at the sun without glasses on, but absolutely look at the total solar eclipse without glasses on. These are two binary events. When you wear glasses and you cannot see anything anymore, that’s totality.”
(Smithsonian.com, July 24, 2017)