Attention stargazers: Thursday afternoon's sunset will coincide with a partial solar eclipse. That means the sun - when spied through eclipse glasses or other special viewing devices - will appear crescent-shaped.
"It's a dramatic event," said Larry Ciupik, senior astronomer at the Adler Planetarium. "You'll be able to see the moon gradually cutting away at the sun, until about half the sun is chopped away."
A partial eclipse occurs when the moon passes between the sun and the Earth, blocking some of the sun's light. The last partial solar eclipse visible in Chicago was in 2012. The next full eclipse for Illinois will be in 2017.
This partial eclipse will begin at 4:36 p.m. Thursday and reach its peak - known as the maximum - at 5:43 p.m.
"It will seem that a bite is taken out of the sun, and that bite will appear to get bigger and bigger as the eclipse progresses," said Michael Smutko, an associate professor in physics and astronomy at Northwestern University. The event should be viewable until sunset, at 6 p.m.
To watch, find a spot with a clear view of the western horizon, and use a pinhole viewer or other piece of equipment specifically designed for solar viewing. One reminder: It's not safe to look directly at the sun without proper eye protection.
Stacking one or more pairs of sunglasses over your eyes will not provide adequate protection, Smutko said.
If you don't have a pair of specially designed eclipse glasses, head down to a viewing party at the Adler, where astronomers will provide expert narration along with solar-filtered telescopes. (For information, visit adlerplanetarium.org.)
Another eclipse-watching event, hosted by Northwestern, will take place on the top floor of the parking garage of the university's visitors center, 1841 Sheridan Road, Evanston.
The weather forecast is predicting partly cloudy conditions. But stargazers are hoping that the skies will remain clear enough to view the cosmic alignment.
"Solar eclipses are relatively rare," Smutko said. "So we are hoping that on Thursday we will get a nice eclipse to tide us over until the next one."