Solar eclipse and your eyes: How to view an eclipse safely
Did you see the 2017 solar eclipse? Did you protect your eyes properly? If you're not sure, here's how to watch a solar eclipse safely.
Solar Eclipse Definition
What causes a solar eclipse? By definition, a solar eclipse is when the moon passes directly (or nearly directly) between the sun and earth, causing the moon to block most of the sun (partial eclipse) or fully block it (total eclipse) for a brief period.
The view from a NASA Gulfstream III aircraft flying 25,000 feet above the Oregon coast during the 2017 total solar eclipse. (Image: NASA)
When Was The 2017 Solar Eclipse?
From beginning to end, the 2017 solar eclipse was visible for about two and a half to three hours, depending on where in the United States you were viewing the phenomenon. The maximum level of the eclipse ("totality"), however, lasted only a minute or two.
On the West Coast, the 2017 solar eclipse began around 9:06 AM and ended around 11:41 AM (Pacific time; Madras, Oregon). On the East Coast, it began around 1:03 PM and concluded around 4:06 PM (Eastern time; Columbia, South Carolina).
For more specific timing, visit the NASA interactive eclipse map. Click on a spot on one of the maps, and an informational box will appear with specific times.
2017 Solar Eclipse Map
Here is a video of what people in different parts of the country saw during the 2017 solar eclipse.Source: NASA
People watching the phenomenon in the center band of the map witnessed a total solar eclipse — where virtually the entire sun was blocked by the moon for a minute or two. States included in this roughly 70-mile-wide "band of totality" include Oregon, Idaho, Wyoming, Nebraska, Kansas, Missouri, Illinois, Kentucky, Tennessee, Georgia, North Carolina and South Carolina.
People viewing the 2017 eclipse from other areas of the map saw a partial total eclipse — where at least a sliver of the sun remained visible at one side of the moon.
Solar Eclipse Glasses: The Best Way To Protect Your Eyes
Solar eclipse glasses are inexpensive, very dark filters with cardboard or paper frames that are designed to protect your eyes from retina damage when viewing an eclipse.
Staring at a solar eclipse (or staring at the sun at any time) can cause a burned retina — called solar retinopathy or solar maculopathy — that can cause permanent vision loss. So having adequate eye protection when viewing a solar eclipse is extremely important.
Certified "eclipse glasses" offer adequate protection from the sun's potentially damaging UV rays when viewing a solar eclipse. Look for documentation somewhere on the disposable glasses that says the eclipse shades are certified to meet the ISO 12312-2 international standard for safe direct viewing of the sun.
Unfortunately, according to the National Science Foundation's American Astronomical Society (AAS), excitement about the 2017 solar eclipse caused the marketplace to become flooded with counterfeit eclipse glasses that say they are ISO-certified when in fact they are not.
Because it's impossible to tell if eclipse glasses truly meet the ISO 12312-2 international safety standard (sometimes written as ISO 12312-2:2015) by simply looking at them, AAS created a Solar Eclipse Task Force that compiled a list of reputable manufacturers and retailers of certified eclipse glasses .
Other Ways To Safely View A Solar Eclipse
If you're unable to purchase ISO-certified eclipse glasses prior to a solar eclipse, using a technique called "pinhole projection" is another way you can view it safely, according to AAS. Though this indirect viewing method is less dramatic than watching directly through eclipse glasses, pinhole projection will protect your eyes from damage.
A solar eclipse occurs when the moon passes between the sun and the Earth. The area of the Earth shaded by the outer shadow of the moon (penumbra) experiences a partial eclipse; the area shaded by the central shadow (umbra) experiences a total eclipse.
To perform this technique, cross the outstretched, slightly open fingers of one hand over the outstretched, slightly open fingers of the other, creating a grid or waffle pattern. With your back to the sun, look at your outstretched hands' shadow on the ground. The spaces between your fingers in the waffle pattern will project a grid of small images on the ground that will show the sun as a crescent during the partial phases of the eclipse.
Another option is to look down at the shadow created by a leafy tree during the partial eclipse. You'll see the ground dappled with crescent suns projected by the spaces between the leaves on the tree, says AAS.
You've probably heard of the "cereal box method," and it does work pretty well (here are simple instructions). Another pinhole method is simply using a pen to poke a hole in a piece of paper or cardboard, holding it in front of you with the sun behind you and letting the eclipse image project onto a sidewalk or wall in front of you.
For more ways to safely view a solar eclipse without certified eclipse glasses, visit this AAS webpage.
Remember, never look directly at the sun with your naked eyes — or use unverified "home remedies" for viewing a solar eclipse.
Also, do not use a camera, binoculars or a telescope to watch an eclipse, unless these devices are equipped with a special filter specifically designed for documenting a solar eclipse. (Don't look at the sun through these devices even while wearing your eclipse glasses or a handheld solar viewer. The concentrated solar rays could damage the filter and enter your eyes, causing serious injury and perhaps even blindness.)
Stuck indoors? Watch NASA TV for live feeds of eclipses and other important celestial events.
Sunglasses Are Not Enough
Sunglasses don't provide adequate eye protection during the course of a solar eclipse.
Though these lenses provide 100 percent UV protection during general wearing conditions, the special-purpose solar filters used in genuine eclipse glasses are thousands of times darker than ordinary sunglasses.
These solar filters are better able to protect the eyes from the intense visible sunlight that can cause a serious retinal injury or even blindness when viewing the sun directly.
When Is The Next Total Solar Eclipse?
If you missed the 2017 total solar eclipse, you'll have to wait awhile to see another one in the United States. The next one to cross North America will take place in April 2024.
Partial solar eclipses will occur in February, July and August of 2018, but only the August one will be viewable in North America.
So you might want to hang onto your eclipse-viewing glasses. But if not, don't throw them away: Astronomers Without Borders is planning a program to collect them for people in developing countries who want to watch future eclipses. Check out their website for details.
Page updated August 2017