Chicagohenge 2025: What is an equinox?

CHICAGO - Chicagohenge is a stunning biannual event that happens during the spring and autumn equinoxes, when the sun aligns perfectly with Chicago’s street grid.

The best views occur at sunrise or sunset, creating a breathtaking sight as the sun frames the city’s skyline.

Here’s a closer look at the science behind equinoxes and how they create this unique phenomenon.

CHICAGO, USA - SEPTEMBER 22: A view of the Chicago's western streets Kinzie and Madison as the sun rises and falls straight down one of two days a year which is known as "Chicagohenge" in Chicago, United States on September 22, 2017. (Photo by Bilgin

Expand

What is an equinox?

What we know:

As Earth orbits the Sun, its tilted axis causes variations in sunlight distribution, leading to the changing seasons.

Twice a year, during the spring and autumn equinoxes, the Earth’s equator receives equal amounts of sunlight, resulting in nearly equal day and night worldwide, according to the Adler Planetarium.

Equinoxes occur around March 21 and Sept. 22, marking the shift between seasons. 

In the Northern Hemisphere, the March equinox signals the start of spring, while the September equinox marks the beginning of autumn. The reverse happens in the Southern Hemisphere, according to the National Geographic Society.

During an equinox, the Sun is directly above the equator, meaning Earth’s axis is not tilted toward or away from the Sun, creating nearly equal lengths of day and night. 

However, atmospheric refraction—where light bends as it passes through Earth’s atmosphere—means day and night are not exactly 12 hours each.

The equinoxes play a key role in Earth’s orbit, influencing seasonal changes, daylight hours, and cultural traditions. 

They also set the stage for phenomena like Chicagohenge, when the Sun aligns with city streets.

As the next equinox approaches, it serves as a reminder of the balance and motion that define Earth’s path around the Sun.

When is Chicagohenge?

Timeline:

This year, you can catch it from March 20 to March 23 during sunrise or sunset:

• Thursday, March 20 – Sunrise at 6:53 a.m. | Sunset at 7:03 p.m.
• Friday, March 21 – Sunrise at 6:51 a.m. | Sunset at 7:04 p.m.
• Saturday, March 22 – Sunrise at 6:50 a.m. | Sunset at 7:05 p.m.

FOR MORE. CLICK HERE.