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Anyone not aware of the upcoming total solar eclipse might be living in a remote cave without so much as a transistor radio. But if that cave is in southern Illinois, they need only step outside at mid-day on Aug. 21 to witness the moon entirely covering the sun. For about two and a half minutes, the sky will turn dark enough for stars and planets to be seen, the temperature will drop, birds will stop singing, and crickets may even start chirping, as nature is fooled into thinking night has fallen.
The Aug. 21 “Great American Eclipse” promises total or partial views from all 50 states, clear skies permitting. A 70-mile-wide “path of totality” in which viewers will see a completely darkened sun runs coast-to-coast, from Oregon to South Carolina. Chicago-area folks wanting to see the whole shebang can travel 350 miles south to the Carbondale area, which lies within the path of totality for this year’s eclipse and again for the April 2024 eclipse.
But there is no need to go farther afield. Here in Evanston we will see the moon cover a generous 86% of the sun, leaving a bright crescent peeking out from the edge of the lunar disk. The eclipse starts at 11:52 a.m. on Aug. 21, peaks by 1:19 p.m., and ends around 2:42 p.m., allowing several hours to view the event from start to finish.
“The thing that I love about this year’s eclipse is the ability for people to witness it, whether it’s totality or any of the partial phases,” says Annie Vedder, Curator of Experience at Chicago’s Adler Planetar-ium. “It’s going to be a phenomenal event that all are going to be able to take part in. And it really doesn’t take a lot of fancy equipment or knowhow to be able to observe this.”
Adler’s “Eclipse Fest” includes viewing events at Museum Campus, Daley Plaza, the Chicago Botanic Garden, and the Morton Arboretum, with free admission to the planetarium, free safe eclipse glasses, telescope viewing, and solar car races.
The Evanston Public Library main branch is also hosting a viewing party from 11 a.m. to 3 p.m. on Aug. 21, with free safe eclipse glasses to the first 120 visitors.
Safe Viewing Options
Although it might be tempting, resist the urge to look up at the eclipse while it is happening. Staring too long into the sun at any time without proper eye protection can cause temporary or even permanent damage to the retina, called solar retinopathy, according to the American Academy of Ophthalmology.
Technically, it is safe to look at an eclipse during the few minutes of totality, when the sun is completely blocked by the moon. But the eclipse will be partial in Evanston, so it is essential to use special glasses for direct viewing, or a homemade pinhole projector for indirect viewing. NASA recommends glasses that conform to the ISO 12312-2 international standard (sometimes written ISO 12312-2:2015). To avoid purchasing unsafe viewing glasses – there have been reports of fakes on the market – the American Astronomical Society provides a list of reputable eclipse eyeglass manufacturers and vendors at tinyurl.com/safe-eclipse-glasses.
Welder’s glass can be used for direct viewing, but it must be rated number 14 and ideally marked as such on the glass itself. Cameras and telescopes must have special safety filters, too.
Easy-to-make pinhole viewers can project the eclipse onto the ground or into a container. The University of Illinois Department of Astronomy provides instructions for making pinhole projectors from a mailing tube or a cereal box at tinyurl.com/safe-eclipse-viewers. Or use certain items around the home or office, with no construction required.
“You can make a pinhole projector out of anything with holes such as a kitchen colander, a Ritz Cracker, and other things around the house,” says Ms. Vedder. “Hold it out toward the sun and look down at the ground to see the crescent shapes. You can even use your hands, and the spaces between your interlaced fingers will project a small grid of the eclipse on the ground.” NASA’s Jet Propulsion Laboratory shows how to create a paper or cardstock pinhole viewer at tinyurl.com/cardstock-viewer.
Holes in tree leaves and the gaps between leaves naturally project layers of beautifully scalloped eclipse images onto buildings, sidewalks, and lawns.
A Chance to Solve the Sun’s Mysteries
Besides being a curiosity for civilian skywatchers, total solar eclipses give scientists rare (about once every 18 months) opportunities to study one of the solar system’s great mysteries: why the sun starts out hot at its core and cools toward the surface, but then unexpectedly goes blazing hot again in its outer layers.
“Imagine I’m heating a pot of water, so the hottest part is where the flame is, and as you get away from the flame it gets cooler and cooler,” explains Robert Rosner PhD, a solar physicist and professor in the departments of Astronomy & Astrophysics and Physics at the University of Chicago. “In the case of the sun it gets cooler and cooler, and then does something really weird: it gets hotter again, as you get further away. So there is some physical process that is heating the corona, and that is what scientists are trying to understand.”
The sun’s core measures 27 million ºF (compared to Earth’s core which is estimated at 10,000ºF). Toward the sun’s visible surface, called the photosphere, things cool dramatically to around 10,000ºF. But then the chromosphere – a thin layer that envelops the sun – heats up to 36,000ºF. And the outermost corona, which shrouds the sun in feathery plumes of ionized gas, rises to a blistering 3.5 million ºF.
On a normal sunny day, light from the photosphere overwhelms the chromosphere and corona, making them nearly impossible for us to see in visible light (the kind of light rays human eyes can detect). To observe and photograph them, special ultraviolet and X-ray telescopes must be sent into space beyond Earth’s atmosphere, which blocks most ultraviolet and X-ray light emissions.
That is when eclipses come in handy. While the photosphere is completely blocked during a total eclipse (the few minutes called totality), its chromosphere and corona become visible around the moon’s border. During totality, scientists look for evidence of sound waves or other kinds of waves emitted at the sun‘s surface that travel into its upper atmosphere – clues that might explain what creates such extreme heat.
“The increase in temperature as one leaves the solar surface goes against everything we believe in the terrestrial context,” Dr. Rosner explains, “so are we seeing some new physics, some new, never-before-encountered phenomenon, or not?”
Solving this particular solar mystery is slow and difficult, he says, because progress depends on the invention of new scientific tools to probe the sun’s light emissions. One such tool – NASA’s car-sized Parker Solar Probe – is scheduled to launch in 2018. It will orbit the sun several dozen times from a distance of four million miles (much closer to the sun than any spacecraft before it), collecting data that could provide clues about the corona.
Folklore, Myths, and Superstitions
Humans have created many stories to explain eclipses, as well as superstitions regarding eclipses’ effects on the world around them. – It was no doubt easy to blame illness, death, natural disasters and other misfortunes on the sun’s frightening and untimely disappearance.
Ancient cultures around the world believed bears, dogs, wolves or dragons had eaten the sun, or at least taken a bite of it. Ancient Greeks believed eclipses foretold catastrophes and destruction. In West Africa, people believed the sun and moon were fighting; to stop the fight, people on Earth had to settle their own differences. Contrary to common superstitions, eclipses do not generate dangerous radiation, are not harmful to pregnant women or their babies, and do not poison food prepared during the event.
Millions of Eyes On the Skies
Approximately 12 million people live within the U.S. path of totality, according to GreatAmericanEclipse.com, which is predicting that anywhere from two to seven million additional eclipse chasers will visit the path of totality on August 21.
To avoid the crush – with its predicted traffic gridlock, port-a-potty shortages, sold-out lodgings, and cellular blackout zones – stay local and enjoy the partial view. Watch from home, with co-workers, at a park or beach, or at any of the area’s viewing events.
“We just want people to be able to go out and safely observe this eclipse,” enthuses the Adler’s Ms. Vedder. “Get your glasses, create a pinhole projector, and just be outside and witness this for yourself.