A friend of mine has been spending more time boating lately, and she recently learned about looking for the green flash at sunset. After several failed attempts at seeing it, she asked me, "is the green flash real?"

What You Need To Know

  • The green flash can occur at sunrise or sunset

  • Skies have to be completely clear

  • You have to have an unobstructed view of the horizon

I told her how the green flash is a real occurrence; You see it when you have clear skies and an unobstructed view of the horizon, such as over water. The conditions have to be just right for it to appear, however.

The AMS Glossary of Meteorology defines it as "a flash of green light seen on or (seemingly) adjacent to the upper rim of the low sun at either sunrise or sunset."

It states, "The green flash is a mirage, but the image formed in this case is of a portion of the sun rather than of an earthbound object. In addition to the displacement and distortion that is characteristic of mirages, there is also significant dispersion."

How it Works

It happens because as the sun dips below the horizon, the sun's rays disperse through the Earth's atmosphere like a prism.

Water vapor in the atmosphere absorbs the yellow and orange colors in white sunlight, and air molecules scatter the violet light. That leaves the red and blue-green rays to be seen by your eyes. 

Near the horizon, the sun’s rays are highly bent as they travel through the atmosphere. This can create an illusion that there are two suns, one that is red and the other that is blueish-green, partially covering each other. 

The red one is always closest to the horizon, so when the sun sets, you might only the blueish-green disk causing an area of green to be visible. As soon as it appears, it is gone, hence why it is referred to as a flash. 

The outer edge of the setting sun usually has a thin, green rim. It is too narrow to be seen by the naked eye unless something obstructs the rest of the sun. In the case of finding the green flash, the horizon would be blocking out the rest of the sun.

The AMS Glossary of Meteorology continues, "it is often asserted that the green flash is seen in this way: a mere transient view of the green rim between obscuration by the rest of the sun and obstruction by the horizon." Such a sequence can produce a single flash of green.

It can also happen as the sun comes up to the horizon at sunrise.

On days where it is entirely clear, and you have an unobstructed view of the horizon, look out for that flash of green, and let us know if you see it! Although, remember to never look directly at the sun without eye protection.

We always appreciate your sunrise and sunset pictures, regardless of whether you happen to capture the elusive green flash. You can share them with us on social media.