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Shedding light on the Aug. 21 solar eclipse: Professors provide answers

by Public Relations and Marketing | Published Aug 11, 2017

Millions of people are expected to flock to Southern Illinois and other U.S. locations Aug. 21 to experience a total solar eclipse, the first time in nearly 100 years that the phenomenon will cross a large portion of the United States. Are you getting curious about eclipses? Wondering what to expect if you remain in Chicago’s northern suburbs.

Professors Eric Priest and Dr. Phyllis Soybel

Here are answers to six common questions, courtesy of two College of Lake County professors, Eric Priest (meteorology) and Dr. Phyllis Soybel (history) (at right):

Exactly what is a solar eclipse, and how does it differ from a lunar eclipse? 

A solar eclipse occurs only when the moon is aligned directly between the Earth and the sun, said Eric Priest, CLC meteorology professor. The widest portion of the umbra (dark portion of the moon’s shadow that is cast upon the Earth) for the Aug. 21 eclipse will be about 68 miles. A total solar eclipse only occurs in the umbra, while a partial eclipse occurs in the lighter part of the shadow (known as the penumbra). A total solar eclipse will occur over portions of Southern Illinois, while Lake County will experience a partial eclipse.

Solar eclipses are rare events due to necessary precise alignments of the sun, moon and Earth as well as the shape of the moon’s orbit around Earth, Priest said. Lunar eclipses occur when the Earth is aligned directly between the sun and the moon.

What can Lake County residents expect to see?

Assuming clouds don’t block the sun, here’s a quick timetable for what will happen:

11:53 a.m.—The moon slowly begins to move in front of the sun. Daylight won’t significantly decrease until about 12:55 p.m.

1:18 p.m.—Daylight quickly decreases to a minimum, as 86 percent of the sun’s disk will be covered and the sky will be eerily dim for a few minutes before it begins to brighten again.

About 1:45 p.m. —The sky will resume its normal brightness for that time of day. To see how the sky will look during the eclipse for any observer in the U.S., visit an educational video co-sponsored by Google and the University of California-Berkeley.

What are the critical safety concerns to keep in mind?  

  • In Lake County, which is outside the zone of totality, it is NOT safe to view the solar eclipse with the naked eye. “Even when 99 percent of the sun’s surface is covered by the moon, the remaining sunlight is still intense enough to cause eye retinal burn,” Priest said.
  • Regular sunglasses are NOT safe to view an eclipse.
  • Inexpensive solar eclipse glasses will be safe— IF they meet the ISO 12312-2 certification requirement. Also, Number 14 welder’s glass is considered safe.

How did pre-scientific cultures respond to eclipses?

Most ancient and medieval cultures, from the Far East to Europe, saw an eclipse as an omen of ill fortune, said Dr. Phyllis Soybel, CLC history professor. The first written observation of an eclipse dates to about the 23rd century B.C. in China. “The Chinese believed that solar eclipses resulted from celestial dragons eating the sun,” Soybel explained. “Eclipses in Chinese history, as with Mesopotamian, Assyrian and medieval English cultures, were associated with bad events. William of Malmesbury, a medieval English astronomer and writer, believed that the eclipse of 1133 A.D. foretold the ‘untimely’ death of King Henry I, who coincidentally died weeks later.”

Once the ideas of the Scientific Revolution began to permeate, and eclipses were better understood as natural phenomena, negative interpretations began to disappear, Soybel said.

What else is good to know about eclipses, including the Aug. 21 event?

At CLC’s Grayslake Campus, approved eclipse-viewing sunglasses will be distributed to 500 students on a first-come, first-served basis at 10:30 a.m. in the Student Commons.

  • The Total Solar Eclipse app from Exploratorium and the Smithsonian Institution’s Solar Eclipse App will live stream the Aug. 21 eclipse.
  • The last solar eclipse to cause nearly as much of the sun’s disk to be covered (as viewed from Lake County) occurred in February 1979.
  • The next significant solar eclipse affecting Lake County will take place April 8, 2024.
  • CLC alumnus Mike Caplan (’82), a meteorologist for Fox 32 News in Chicago, is providing eclipse updates and information on his Facebook page @MikeCaplanMeteorologist.

How can I learn more about eclipses and other earth science topics?

At CLC, you can learn more about eclipses in ESC 120 (Earth Science), ESC 140 (Introduction to Astronomy with Lab) and ESC 141 (Introduction to Astronomy). CLC’s Fall Semester courses begin Aug. 21, and many late-starting classes are available. To view fall course offerings and learn how to become a student, visit www.clcillinois.edu/fall.