Don't stare. It's not just good etiquette — when it comes to a solar eclipse, it might save your vision.
Even though the moon will cover nearly half the sun during Thursday's partial eclipse, that limited amount of light can still pack a punch on the rods and cones in our eyes.
UCLA ophthalmology professor Dean Bok said that's because, even during an eclipse, the sun casts enough photons to create dangerous chemical changes in our eyes.
As part of normal vision, photons trigger a complex chemical reaction that sends packets of sight to our brain. This process also produces harmful byproducts called "free radicals" — loose ions looking to latch onto something. Free radicals are highly reactive and can damage cell membranes and even DNA.
According to Bok, our body normally removes these free radicals ,but when there's too much light flooding the eye, those processes are overwhelmed.
"The cells that would normally handle that load are incapable of doing so anymore, so that tips it over into 'damaging mode,' if you will," Bok said.
While those excess free radicals are wreaking havoc on eye cells, the heat from the sunlight starts to take its toll. Bok says this thermal energy can "cook" the proteins in the eye, warping their shape in a process called "denaturation."
"A good example is when you drop an egg white into hot water — when it turns white, that's denaturation," Bok said.
This one-two punch of chemical and thermal reactions can cause temporary or even permanent vision loss, he added.
Fortunately, there are several ways to safely experience a solar eclipse. First, you can purchase special sun viewing glasses.
You can also build a pinhole projector or watch a live stream of the event from the safety of your computer:
This story has been corrected.