In this perfectly timed photo we see the setting sun in Chicago during Spring Equinox on 20 March 2014. Taken by Flickr user niXerKG, who dubbed the photo Chicagohenge, he says you can see the setting/rising sun in the streets of Chicago that run east/west.

An equinox occurs twice a year, around 20 March and 22 September. The oldest meaning of equinox is: the day when daytime and night are of approximately equal duration.

An equinox occurs when the plane of Earth’s Equator passes the center of the Sun. At that instant, the tilt of Earth’s axis neither inclines away from nor towards the Sun. The two annual equinoxes are the only times when the subsolar point—the place on Earth’s surface where the center of the Sun is exactly overhead—is on the Equator, and, conversely, the Sun is at zenith over the Equator. The subsolar point crosses the equator, moving northward at the March equinox and southward at the September equinox. [source]