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Bianca Anderson
Digital Marketing Specialist

As a self-proclaimed "space nerd," Bianca relishes in the opportunity to champion the Adler's mission to the public every day. In her free time she enjoys eating Popeyes' $5 Bonafide Box, attending indie-music shows, and checking out all of the world-class museums that Chicago has to offer.

AstroFan: Understanding Chicagohenge

Pedestrians walking (during Chicagohenge) across a crosswalk while the Sun sets in the distance with the Willis Tower in view.

Header Image: Chicagohenge as seen from West Adams Street. Image Credit: Tim Hara


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 interestinglet’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!

A bird's eye view of Chicago at night, with the city's gridline highly visible.
Bird’s eye image of Chicago’s grid taken at night. Image Credit: NASA/ISS

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/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.

Just as an FYI, Chicagohenge is named after the famous prehistoric monument, Stonehenge. 

Just like Chicagohenge, during certain times of the year the Sun lines up with the monoliths, forming an impressive spectacle to behold!

Now that we’ve got the basics of Chicago’s grid mapped outlet’s dive into the role that equinoxes play in the makings of a 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 nighthence 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 and How to see Chicagohenge

Be on the lookout for Chicagohenge this week on Thursday, March 19. The best time to view the Chicagohenge is around sunset or sunrise on the day(s) leading up to and on March 19.

Finding a place to spot Chicagohenge is a no-brainer! Simply find one of Chicago’s east-west facing streets, plop a seat, and enjoy the view. 

The Sun sets during a Chicagohenge as a CTA train travels towards it.
Image Credit: @cdats

If you do decide to check it out, snap a pic and tag the Adler @adlerplanet. It’s sure to be a sight worth stopping to look at!

Stay tuned for more awesome space facts on the next AstroFan.

Thank you for reading!

—Bianca, a.k.a. AstroFan


Note: When viewing Chicagohenge, please keep in mind the CDC recommendations for maintaining social distance to curtail the spread of COVID-19. Avoid viewing Chicagohenge in large groups, maintain a distance of six feet from other people, and avoid using public transport. For more information regarding social distancing visit the official website of the CDC.

FOLLOW US!

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Author Bio

Bianca Anderson
Digital Marketing Specialist

As a self-proclaimed "space nerd," Bianca relishes in the opportunity to champion the Adler's mission to the public every day. In her free time she enjoys eating Popeyes' $5 Bonafide Box, attending indie-music shows, and checking out all of the world-class museums that Chicago has to offer.

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