Tomorrow, much of North America, including Chicago, will be able to see a partial solar eclipse. That is, the New Moon will pass in front of the Sun, partially obscuring the disc of the Sun. The Sun will look like a crescent.
It should go without saying: Do not look directly at the Sun–even when it is eclipsed!
In Chicago, the eclipse begins at 4:36 pm CDT. The maximum eclipse, when the Moon covers 44% of the Sun, occurs at 5:43 pm CDT. Sunset is at 5:56 pm CDT.
Yes, the Sun will set during the eclipse, which should provide some interesting photography possibilities.
Here are few posts from Universe Today about the eclipse: