The total solar eclipse on August 21, 2017 is kind of a big deal.
On August 21, 2017, for the first time in 99 years, a coast-to-coast solar eclipse will be visible across the continental US. This means that just about anyone in those 48 states will be within a day’s drive of seeing a total solar eclipse. In other words, if you will be in the US on August 21, this is pretty much the total solar eclipse of a lifetime.
Depending on where you are in the US, you’ll see either a partial or total eclipse.
“The moon will totally block the sun for up to two minutes and 40 seconds, as seen from within a roughly 70-mile-wide path stretching from the Oregon coast to the South Carolina coast,” Rick Fienberg, astronomer and press officer for the American Astronomical Society (AAS), writes in an email to BuzzFeed Health. This 70-mile swath is called the “path of totality” — where you’ll see the sun totally blocked by the moon. And if you’re there, says Fienberg, “you will see the most spectacularly beautiful sight you have ever seen in nature.”
Outside the path of totality, you’ll get to see a partial solar eclipse, “in which the moon glides across the sun, blocking part of it but never covering it fully,” Fienberg says.
But there’s a catch. Looking directly at the sun — even when it’s partially blocked by the moon — is dangerous.
Other than the brief moment when the moon completely blocks the sun (if you’re in the path of totality), the eclipse must be viewed with special solar filters that are certified to meet international safety standards, says Fienberg. (More on those and eclipse-viewing safety shortly.)
So, what exactly happens when you look at the sun? Turns out that although you probably won’t go totally blind, you can get super serious, permanent eye damage in less than 30 seconds. Yikes.
Let’s start with a quick primer on how the eye works.
The different parts of the eye work together to create vision. The iris, the colored band around your pupil, opens and closes your pupil to control how much light enters the eye. The cornea is the front of the eye; it bends the incoming light. The lens is behind the pupil, and it focuses light onto the retina, a delicate tissue that’s located in the back of the eye. There are light-sensitive cells on the retina that detect light coming from the lens, and process it into information that then gets sent to the brain via the optic nerve. From there, the brain decides what to make of this information.
It’s a part of the retina that is at risk of being damaged by exposure to sunlight.
At the center of the retina is the macula, which is responsible for what we see right in front of our eyes — it provides the sharpest sight. If the macula is damaged, you’ll go from seeing sharp detail in the center of your vision to seeing a dark grey or black spot, says Dr. Joel Schuman, professor and chair of the Department of Ophthalmology at NYU Langone Medical Center.
And unfortunately the macula is uniquely vulnerable to sunlight damage.
This is because the retina is thinnest at the macular region, making the retina’s protective outer layer (the retinal pigment epithelium or RPE) most susceptible to sun damage in that area. “Think of it like the skin of your body; your eyelid skin is thinner than the skin on your heel,” says Dr. Ranya Habash, ophthalmologist at Bascom Palmer Eye Institute and consultant for TopLine MD, explaining the difference between the RPE at the macula and other parts of the retina.
You really don’t have to look at the sun for very long at all for photochemical toxicity to occur, says Schuman. Retinal damage could occur in just 30-60 seconds, and sometimes even less, he says. Once the retina is exposed to sunlight damage, the macula’s cells are damaged, rendering them unable to properly process visual information, says Habash. This is when you end up with dark spots in the center of your vision.
And most of the damage is permanent.
Once the retina’s cells have experienced photochemical toxicity, Habash says “there’s not much we can do about it.” Although some of the damage may correct itself over time, and the area around the burn might recover some vision, there’s no real treatment that will reverse the damage. You could be left with permanent, “disabling” vision loss, says Schuman.
Having said all that, there are ways to safely view a solar eclipse.
Here are the the main things to know:
• Regular sunglasses — even really dark ones — will not protect your eyes from sun damage. Just to illustrate how inadequate even the darkest ordinary sunglasses would be for eclipse viewing, according to Fienberg, certified solar eclipse-viewing glasses are 1,000 times darker than ordinary sunglasses. ONE THOUSAND TIMES.
• According to the AAS, you should only view an eclipse through special-purpose solar filters that meet the ISO 12312-2 international standard for these products. You can buy special eclipse glasses or viewers that allow you to look at an eclipse safely.
• If you view an eclipse through binoculars or a telescope that don’t have special eclipse-safe filters, more light is concentrated onto the retina, Fienberg says, which puts your eyes at even more risk. If you want to use binoculars or a telescope (or any optical device including a camera), you must get special eclipse-safe filters for the front lenses.
And by the way, if you’re in the path of totality, there will be a moment when you can remove your special protective lenses: when the moon blocks the sun completely and it gets completely dark. But as soon as the sun begins to reappear, you must put your special glasses back on.
