You can damage your eyes in mere seconds during the solar eclipse

On August 21, as the moon slips between the Earth and the sun, millions of people around the United States will look skyward to watch the one-in-100 year event.

Many will be tempted to look at the sun with their naked eyes. In fact, it's often tempting to look at the sun, to challenge yourself to do something strictly forbidden by parents, teachers, and doctors.

But in this particular instance, it's forbidden for a reason.

Even though a total solar eclipse will effectively blot out all of the sun's light during totality, the powerful light from our closest star can still cause eye damage in a matter of seconds during the partial phases of the eclipse, according to optometrist James Vann.

"While age and pigmentation of the eye will affect how quickly you’re impacted by harmful light, looking at the sun poses an immediate risk for eye damage," Vann, a Transitions pro forum member, said via email.

"Children are particularly at risk as they have virtually no natural protection," Vann added.

Even if most of the sun is covered, the star is still so bright that it can cause eye damage.

The sun's light can effectively burn your eyes the way it can burn your skin.

"The brightness and intensity of harmful light damages the focal point of your eye," Vann said.

"Sometimes this can be reversed, but many times it is permanent. The sun’s damage is cumulative, so the effects of looking at an eclipse may not show up until years later or it may cause immediate damage."

The only time it's safe to look directly at the sun during an eclipse is during totality, those brief minutes when the sun is completely covered by the moon.

Only people in the 70-mile-wide path of totality that runs from Oregon to South Carolina will be afforded that view of the moon fully blocking the sun, so anyone outside of that relatively small part of the country will need some heavy-duty eye protection.

All of North America will be treated to at least a partial eclipse Monday, so if you want to take part, definitely get some eclipse glasses or build your own eye-safe viewer.

"If you look at the sun without eclipse glasses during a partial eclipse, or on a regular day, you are going to fry the back of your eye," Vann said.

"Looking at the sun is not wise, and I have serious doubts about how safe the cheap eclipse glasses are for your eyes."

Vann is right to be somewhat worried about the efficacy of eclipse glasses.

Amazon.com recently recalled a number of eclipse glasses due to safety concerns, and the counterfeit market for this eyewear has grown this year in anticipation of the big event.

That said, if you go to a trusted source and provider of eclipse glasses, you should be okay.

Some optometrists, including Vann, also suggest that people watch the eclipse online through NASA or other broadcasters instead of looking to the sky. You can also create a pinhole projector to view the eclipse indirectly outside.