Understanding Chicagohenge
Header Image: Chicagohenge as seen from West Adams Street. Image Credit: Tim Hara
Update: This blog was originally published in 2020 and written by Bianca Anderson. It is revised each year with updated dates of Chicagohenge and the equinoxes.
Greetings fellow Chicagoans! It is almost that time of year when nature and architecture harmoniously come together to create the phenomenon known as Chicagohenge.
For those who don’t know, Chicagohenge occurs twice a year and happens when the Sun directly lines up with Chicago’s east-west facing streets.
Not only is this event a beautiful sight to behold, but the science behind it is quite interesting—let’s dive in!
About Chicago’s Grid
To fully understand Chicagohenge, you have to be aware of the two main factors that cause it: Chicago’s grid plan and equinoxes.
Let’s first touch on the grid plan that Chicago was built on. A grid plan is when the streets of a city run at right angles to each other forming a (you guessed it) grid!
The present-day Chicago grid system can be attributed to the Public Land Survey System—a surveying method created in 1785 that was used to divide land for selling and settling. But this style of city design has been around since the dawn of civilization and can be found in the ruins of ancient Rome, Greece, and others.
The benefits of a grid plan are numerous. They help make cities more walkable, navigable, and adaptable. Plus they end up resulting in cool astronomical and architectural events (like Chicagohenge)!
Fun fact: Chicago’s streets line up almost perfectly with the cardinal east and west directions on a compass. This in turn, sets up the perfect stage for Chicagohenge to take place.
Chicagohenge is named after the famous prehistoric monument, Stonehenge. A sculpture similar to this familiar giant stone monument, America’s Courtyard, can be found on the right side of the Adler Planetarium when approaching the building. The installation can be used to mark the Sun’s passage through the seasonal equinoxes and solstices.
However, did you know that Stonehenge isn’t actually a henge after all?
@adlerplanet #Chicagohenge is actually a little sus…#Stonehenge #LearnOnTikTok #SpaceScience #Science #Chicago
Now that we’ve got the basics of Chicago’s grid mapped out—let’s dive into the role that equinoxes play in the makings of Chicagohenge.
Equinoxes 101
As the Earth orbits around the Sun, it is also spinning along its tilted axis.
Since the Earth’s axis is tilted, sunlight is not always distributed equally. At any given point, one-half of the Earth is tilted towards the Sun more than the other. As the Earth orbits around the Sun, the part that was tilting away from the Sun begins to be the part that is facing towards the Sun. This is why we have seasons!
There are two times during the year when the Earth’s equator receives most of the sunlight. When this happens, our planet’s Northern and Southern Hemispheres experience equal amounts of day and night—hence the term equinox.
There are two equinoxes each year, one that marks the start of spring (Spring Equinox) and one that marks the end of summer (Autumn Equinox).
During an equinox, the Sun rises and sets directly to the east and west.
Thanks to Chicago’s perfectly lined grid system, the bi-annual equinoxes mark a time when the Sun rises and sets directly in line with Chicago’s east and west streets, causing Chicagohenge!
When is Chicagohenge 2025?
Be on the lookout for Chicagohenge dates on March 20–23, 2025 and September 22–25, 2025. The best time to view Chicagohenge is when looking due east or due west around sunset or sunrise on these day(s) leading up to or after the equinoxes.
Thursday, March 20, 2025: Sunrise at 6:53 am and sunset at 7:03 pm
Friday, March 21, 2025: Sunrise at 6:51 am and sunset at 7:04 pm
Saturday, March 22, 2025: Sunrise at 6:49 am and sunset at 7:05 pm
Sunday, March 23, 2025: Sunrise at 6:48 am and sunset at 7:06 pm
Monday, September 22, 2025: Sunrise at 6:38 am and sunset at 6:47 pm
Tuesday, September 23, 2025: Sunrise at 6:39 am and sunset at 6:45 pm
Wednesday, September 24, 2025: Sunrise at 6:40 am and sunset at 6:43 pm
Thursday, September 25, 2025: Sunrise at 6:41 am and sunset at 6:41 pm
Best Spots to View Chicagohenge
Finding a place to spot Chicagohenge is a no-brainer! Simply find one of Chicago’s east–west facing streets, pick a spot 5-10 minutes before sunrise or sunset, and enjoy the view.
If you do decide to check it out, snap a pic and tag @adlerplanet and #Chicagohenge on your favorite social media channels! It’s sure to be a sight to behold.
Learn From Our Astronomy Educators
In a previous Sky Observers Hangout episode, our astronomy educators show you how to observe equinox sunrise and sunset alignments in your area and how to photograph Chicagohenge!
Watch the full Chicagohenge episode and subscribe to our YouTube channel to stay up to date on upcoming cosmic happenings and even see celestial objects through a telescope virtually.
