This story has been updated.
It's the final countdown to the first total solar eclipse to cross the country coast to coast in nearly 100 years.
» RELATED: 7 things to know about the rare total solar eclipse crossing the nation this August
The Aug. 21 total solar eclipse marks the first to cross the continental U.S. from coast to coast in nearly 100 years.
If you’re one of the many planning to make your way near the path of totality to watch the celestial spectacle, there are some serious safety precautions to consider.
» RELATED: How Georgians can watch the rare total solar eclipse this summer
Here are nine things to know about solar eclipse damage and safety from a variety of experts to ensure you have as safe an experience as possible:
1. Yes, a solar eclipse can blind you.
According to Ralph Chou, professor of optometry and vision science at the University of Waterloo in Canada, “even the tiniest sliver of a crescent sun peeking out from behind the moon emits enough light to scorch your eyes.”
Chou told Space.com that he's seen patients with crescents "burned into the back of the eye," enough so that he can almost tell exactly when they looked up at the sun.
This happens because sunlight can trigger chemical reactions in the retina and leads to what doctors call a retinal photochemical injury or solar retinopathy.
And in severe cases, when people don't use protection or stare at the sun for an extended time, sunlight damage can come with literal "sunburns" that destroy the rods and cones in the retina, Space.com reported.
» RELATED: This is the most accurate map of the Great American Eclipse’s path of totality to date
2. The risk of sunlight damage to your eyes is exacerbated during a solar eclipse.
Most of us grew up learning not to stare at the sun for a long period of time and find it uncomfortable to do so at all, so it’s rare for someone to risk being blinded by the sun.
During a solar eclipse, however, that risk is increased because looking at a partially covered sun might feel more comfortable to the human eye and human instinct.
But, Chou said, that tiny crescent that remains during a partial eclipse is still bright enough to burn your retinas.
3. You probably won't notice you damaged your eyes until the next morning.
According to Chou, this is what makes eclipse blindness particularly dangerous.
“Let's say you take a look at the sun in the afternoon. The cells get overloaded, and they're actually still able to function for a little while, but overnight while you're asleep … the cells start lose their function, and then they even start to die depending on exactly how badly they've been affected,” he said.
When they wake up, they may find their vision to be impaired, particularly the center of vision (the part of the retina responsible for seeing in hi-res and in color).
4. Most patients with eclipse blindness are legally blind when they visit an eye doctor.
The most unfortunate part about eclipse blindness is knowing what the ultimate prognosis is going to be, Chou said.
It could take the typical person six to 12 months before knowing whether or not they will remain legally blind or recover.
According to Chou, about half of patients diagnosed with eclipse blindness fully recover, regaining full vision, in six months. But the other half partially or never recover.
There aren’t really any treatment options and doctors treat the impairment like any other case of visual impairment.
5. So, when is it safe to look at the sun with the naked eye during a solar eclipse?
According to NASA, during a solar eclipse, you should not look directly at the sun without protection except during the brief totality time.
For example, in Rabun County, the Aug. 21 total solar eclipse will begin at 2:35 p.m. and last for 2 minutes and 40 seconds. That 2 minutes and 40 seconds marks the brief totality time in which you are safe to look at the sun without any official protection gear.
You can use this Google simulator to determine the narrow path of totality from wherever you expect to tune in on Aug. 21.
» RELATED: What will the sky look like in your city during August’s rare total solar eclipse?
6. The only safe way to view the partially eclipsed (or un-eclipsed) sun directly is to wear eclipse glasses or hand-held solar viewers.
Only select manufacturers have certified that their products meet the ISO 12312-2 international standard for eye and face protection.
American Astronomical Society- and NASA-approved eclipse glasses, filters and handheld viewers:
- Rainbow Symphony Eclipse shades
- OUT OF STOCK as of Aug. 10
- American Paper Optics Eclipser
- Minimum order: 25
- Thousand Oaks Optical Silver-Black Polymer and SolarLite sheets
- OUT OF STOCK as of Aug. 15
- TSE 17 Solar Filter foil
- OUT OF STOCK as of Aug. 15
- Celestron EclipSmart glasses and viewers
- OUT OF STOCK as of Aug. 15
- DayStar Solar glasses
- OUT OF STOCK as of Aug. 10
- Explore Scientific Solar Eclipse Sun Catcher glasses
- OUT OF STOCK as of Aug. 10
- Lunt Solar Systems SUNsafe SUNglasses
- OUT OF STOCK as of Aug. 15
- Meade Instruments EclipseView glasses and viewers
- OUT OF STOCK as of Aug. 10
- Seymour Solar Helios Glasses
- OUT OF STOCK as of Aug. 10
- Baader Planetarium’s AstroSolar Silver/Gold Film
- OUT OF STOCK as of Aug. 15
NASA also warns against using homemade filters, sunglasses (no matter how dark) or unfiltered cameras, telescopes, binoculars or other unfiltered devices when looking at a partially-eclipsed or un-eclipsed sun.
Additionally, if the glasses are older than three years or have scratched/wrinkled lenses, they should not be used.
You should not look at a partially eclipse or un-eclipsed sun using an unfiltered camera, telescope, binoculars or other optical device, NASA warns.
7. If you're using a telescope, make sure it has a solar filter.
Never look through a telescope without a solar filter on the large end of the scope, NASA warns.
And don’t use small solar filters that attach to the eyepiece, which are common in older products.
8. Where to get safe eclipse glasses and handheld solar viewers
Eclipse2017.org offers a list of eclipse glasses sold in bulk (packs of three to 200) with net prices ranging between $1.08 to $3.90.
You can also purchase eclipse glasses at a variety of stores or sites, including at the official manufacturer's website or at Amazon.com.
Additionally, several libraries around the country will be giving away eclipse glasses starting in August.
Official manufacturer prices:
Prices for Rainbow Symphony viewers and glasses start at $0.45.
American Paper Optics sells its products in bulk, with the cheapest option being a pack of four eclipse glasses for $12.
Thousand Oaks also sells its products in bulk, with the cheapest options being a pack of 25 solar viewer cards or glasses for $35.
The price for a single pair of glasses from TSE 17 starts at $0.98.
More about pricing, shipping and where to order eclipse glasses at eclipse2017.org.
9. How to use eclipse glasses and solar viewers the right way, according to NASA
- Make sure your solar filters, glasses or viewers aren't scratched or damaged before using.
- Don't look at the uneclipsed or partially eclipsed sun through an unfiltered camera, telescope, binoculars or other optical device. The solar rays will damage the filter and enter your eyes, causing serious injury.
- Stand still and cover your eyes with your glasses or viewer before looking at the sun.
- Do not remove the filter, glasses or viewer while you're still looking at the sun. Instead, after glancing at the sun, turn away and then remove.
- Only remove the solar filter if you're within the path of totality and only during totality, when the moon completely covers the sun's brightness.
- As soon as the sun gets brighter again and totality is over, bring back the eclipse glasses or solar viewer.
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