Twice a year the sun lines up with Chicago’s architecture in a phenomenon called “Chicagohenge.”

Chicagohenge is when the sun appears to be perfectly framed between the skyscrapers of Chicago. It occurs when the path of the sun aligns with the equator, rising and setting directly east and west.

Because Chicago’s streets are arranged in a grid system, the sun appears centered between the buildings on streets that align east-west.

This phenomenon only happens during the spring and fall equinoxes.

According to the Adler Planetarium, solar equinoxes are the only times of the year when sunlight is distributed evenly, meaning everywhere on earth will experience equal amounts of daylight and night.

The days surrounding equinoxes are when Chicagohenge can be witnessed.

This year, spring Chicagohenge will begin on March 19 and continue until March 23. The equinox is on March 20.

The best time to view the event will be during sunrise or sunset on streets facing due west or due east.

Tuesday evening will be an ideal time to watch as the weather is expected to be mostly clear.

You can learn more about Chicagohenge and equinoxes at adlerplanetarium.org.