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AccuWeather logo AccuWeather 5/13/2021 Brian Lada

Two days a year, part of the world experiences an unusual natural phenomenon that can make objects in the real world almost look like they were photoshopped.

For just a few brief moments on these specific days, all sorts of things -- from flag poles to bicycles to people walking down the sidewalk -- cease casting a shadow.

Not every area of the world gets to experience this astronomical occurrence, including western Pennsylvania, where Punxatawney Phil, who relies on his shadow for his annual weather prognostications, lives.

Zero Shadow Day happens twice a year for areas in the tropics when the sun is directly overhead in the sky. As a result, it appears as though vertical objects do not have a shadow.

This event is also called "Lāhainā Noon" in Hawaii, the only state in the U.S. that experiences the bi-annual solar event.

Lāhainā when translated into English means "cruel sun," according to Bishop Museum in Hawaii, since it is when the sun's rays are the strongest compared to the rest of the year.

a bicycle parked on the side of a road © Provided by AccuWeather
The shadow of a bike-shaped object was only visible directly below it during Lāhainā Noon in Hawaii on May 25, 2019. (Flickr / Daniel Ramirez)

The reason Zero Shadow Day can only be experienced from a tropical location has to do with the tilt of the Earth.

On the day of the equinoxes, which occur around June 20 and Sept. 20, the light from the sun is directly over the equator with light from the sun hitting the ground at a perfect 90-degree angle. This makes the equinox the Zero Shadow Day for towns located precisely along the equator.

diagram © Provided by AccuWeather
This image shoes how the direct rays from the sun are over the equator on the day of the equinox. (NASA)

The direct rays from the sun gradually shift north in the months leading up to the June solstice with the sun appearing directly overhead from the Tropic of Cancer in the Northern Hemisphere around June 20.

After this, the direct rays from the sun shift southward each day until the December equinox, when the sun appears directly overhead from the Tropic of Capricorn in the Southern Hemisphere around Dec. 20.

Because of this back-and-forth motion similar to a windshield wiper, all of the areas in between the Tropic of Capricorn and the Tropic of Cancer experience the sun directly overhead two times a year.

diagram © Provided by AccuWeather
Only the areas located between the Tropic of Cancer and Tropic of Capricorn (shown in red) can experience a Zero Shadow Day. (WikiMedia Commons/KVDP)

In Hawaii, these two dates fall during the second half of May and the middle of July, but the exact dates of Zero Shadow Day vary from island to island.

This year in Honolulu, Lāhainā Noon falls on May 26 and July 16, according to Bishop Museum.

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Mexico City, Mexico, San Juan, Puerto Rico, and Chennai and Bengaluru, India, are a handful of other big cities around the globe that experience Zero Shadow Day twice a year.

For folks that live north of the Tropic of Cancer or south of the Tropic of Capricorn, careful planning to the tropics is a necessity to witness the solar phenomenon.

Even after weeks or months of planning to be at a specific point for Lāhainā Noon, cloudy conditions could ruin the event.

Shadows disappear for just a few minutes around midday, so just one poorly-timed cloud could spoil the show.

Keep checking back on AccuWeather.com and stay tuned to the AccuWeather Network on DirecTV, Frontier, Spectrum, FuboTV, Philo, and Verizon Fios.

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