On Monday, August 21, a rare total eclipse of the sun will be seen along a 70-mile-wide path stretching from Salem, Oregon to Charleston, South Carolina. The eclipse will travel faster than the speed of sound, crossing the entire United States in roughly 90 minutes. Its path crosses southern Illinois, marking the first time since 1869 that a total eclipse has been visible from our state.
This eclipse is the first in a series of three “American eclipses” that will follow similar paths from coast to coast. The other American eclipses will occur April 8, 2024 and August 12, 2045. The last total eclipse visible anywhere in the continental United States occurred in 1979.
Solar eclipses occur when the moon comes directly between the sun and the earth, blocking our view of our local star. In a total eclipse, the moon blocks the entire sun. If part of the sun still sticks out, it’s a partial eclipse. Total eclipses are special because they allow us to see the outermost layers of the sun, called the chromosphere and the corona. Those features are normally invisible in the sun’s bright glare, and cannot be seen in a partial eclipse.
On August 21, the Naperville area will see a deep partial eclipse, but not a total eclipse. Almost 90 percent of the sun’s disc will be blocked by the moon when the eclipse reaches its maximum extent at 1:19PM. Because the sun will not be completely blocked, you must use “eclipse glasses” or other devices specifically made for solar viewing in order to safely view the partial eclipse, or risk permanent loss of vision.
Eclipse glasses are available for purchase at all public events sponsored by Naperville Astronomical Association, while supplies last. For details, visit www.naperastro.org.
—Rick Gering
Naperville Astronomical Association Public Outreach
Editor’s Note / Thanks to Katie Wood for putting PN in touch with Dr. Adam Black, O.D., at Couture Vision in downtown Naperville. We wondered about eyeglass and viewer safety to watch the eclipse on Aug. 21, 2017, and Dr. Black provided his professional wisdom.
“Special solar filters (either in eyeglass or viewer form) are necessary to be able to view the eclipse,” noted Dr. Black. “There are great tips for safely using them on NASA’s website, and you want to be sure to get those with a safety rating of ISO 12312-2 which is the international standard of safety. NASA and the American Astronomical Society have listed reputable vendors that have shown to be using certified manufacturing techniques (eclipse2017.nasa.gov/safety and eclipse.aas.org, respectively).
“While these products can be ordered online, I have seen a number of alerts coming through the American Optometric Association regarding “fake” eclipse glasses being sold that aren’t offering the proper level of protection.
“The ONLY time you may view an eclipse safely without a solar filter is during the few minutes of 100% eclipse totality. With Naperville being outside the zone of totality, everyone in the area should be using these to view the eclipse. Otherwise, significant damage to the retina may occur, and a solar burn can cause permanent blindness.
“Obviously, this is a major astrological event that shouldn’t be missed. We just want to make sure that it’s experienced safely.”
