Ever seen a green flash at sunset? Here's why it happens.

As the sun sets and the light starts to dim, some lucky onlookers may spot a rare, brief flash of emerald green. This is known as the ‘green flash’, which can sometimes be witnessed right after sunset or before sunrise.

What causes the green flash?

Sunlight, like a rainbow, has a hidden punch of color. Normally, it appears white because it blends all the colors of the visible spectrum.

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But when sunlight dives towards the horizon, it travels through a thicker layer of air. This air acts like a prism, bending different colors at slightly different angles.

This winding is called refraction, and this is why we sometimes you see emerald green flash at sunset or sunrise.

Refraction is noticeable when the sun gets closer to the horizon, because sunlight is entering the thickest part of the atmosphere at a particularly sharp angle. This is when the green flash may be visible.

How to witness the green flash?

In coastal areas like San Francisco, one can most likely spot the green flash on warmer days, when there's a layer of warm air on top of colder water, said Jan Null, a meteorologist based in California.

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You also need to be able to have a direct line of sight of the sun on a clear day to see the green flash, which is easier said than done. So Null recommended using a camera with a zoom lens to capture the green flash, zooming in on the sun also makes tiny flashes more visible.

Green flashes usually happen in less than a second. But if you're lucky, a green flash could shine for a minute or two.

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"It's really weird when you see green in the sky," Courtial said, which is likely why the green flash is so intriguing. So, the next time you're watching a sunset, indulge in that fascination. Now, you know more on how it happens.

(With inputs from agencies)