What’s With That Mysterious Green Flash People See at Sunset?

Photography students bring me many questions about the environment they photograph. The green sunset flash question is one of them. Is it myth or fact? They want to know if the green flash is real and, if it is, how to capture it.

Some of you will think my post’s headline is part of a hoax. Others might believe it’s a myth owing to something they vaguely remember hearing about a long time ago. I get that.

The story seems far-fetched to me too.

When I heard about the green flash at sunset story the first time, I wasn’t convinced. I’d never seen such a flash of light — and I’d seen enough sunsets to know if it did!

And to be honest, ninety-nine percent of my students never knew of it either. It was an enigma to everyone.

Of course, once a class became aware of it, everyone was fascinated. They wanted to know the deal, me included. The first instance this happened was way back in ’96.

“What causes it?” A student asked.

I raised an eyebrow and replied, “A green flash? Really? When does this happen?”

“Like I said, when the sun goes down. They say there’s a flash of green light.”

“Have you seen it?”

“No, but they say it happens.”

They? I didn’t know who they were. The student couldn’t state the ubiquitous they and I was left wondering who they might’ve been. We had a bit of fun with the topic and then we moved on.

I put it down to cross-contamination of information — bits of stories thrown together that created a brand new one. And then I was asked about it a year later, and then again during the following semester. I started to take notice. It was enough to make me consider that there was some substance to the story. Each time it came up, I turned the question back over to the rest of the class to see how many students were aware of it.

“Has anyone else seen or heard about this green flash that appears at sunset?”

A resounding no came back from the groups I taught. No one apart from the student who raised the issue (but never saw the flash) was aware of the flash story. I was perplexed about this strange atmospheric event that seemed to exist yet didn’t exist at all. What was the source of this strange tale?

Clearly, something supported it enough to emerge in the human psyche. The flash wasn’t yellow or purple. It was always green. That’s a pretty specific detail. And what could cause a flash of light to occur in the first place?

My thoughts turned towards the physics of light.

Photographers know of the colour change that occurs in the sun as it descends in the afternoon sky. It’s called redshift. Earth’s atmosphere causes the sun’s light to split into a rainbow of colors through refraction. The last one is red. The setting process leaves the red spectrum of light to make its way to viewers and photographers on the ground around sunset. The lower the sun goes, the redder it appears to be.

My green flash theory was tied to this transition. I believed that some part of the green spectrum was being bent, revealing itself ever so briefly in the sunset’s final stages. It was only a working theory as I came across no document to prove that the flash even existed (at the time, the Internet was new and evolving).

And then, in early 2002, I saw it for myself, or at least I thought I did. It was quick. Easy to miss. The sun was no longer in the sky. Yes, it was real, small, and subtle, not what I expected at all. I’ve always anticipated it to be a blinding flash of light, but this was barely noticeable at all. It was definitely green in colour.

So, there are two special conditions to factor in when hunting down this mysterious green flash:

• It comes after the sun vanishes.
• It’s subtle (don’t think flash; don’t even think pulse).

This explains why so few people have seen it or know about it. Even those who are in a position to watch a sunset will still miss it when it’s happening. I’m sure if a hundred people were watching the same sunset at the same time from the same vantage point, only one or two would recognize the moment when it occurs and then doubt themselves a moment later.

Where Does This Tale Come From?

The origins of the story go back hundreds of years. Ancient sailors with nothing to do but look at the sky every day became extremely sensitive to the sun’s behaviour. Any sudden change in the sun would’ve easily been described as a flash.

Unfortunately, that description doesn’t compare to the kinds of flashes we see in modern life. Today’s flashes are made to make bold statements or to momentarily illuminate areas of space for picture-taking purposes. They are not used to describe this kind of behaviour in light. We’d describe what those early sailors saw as a momentary glow, not a flash.

Secondly, it’s not exclusive to sunsets. Sunrises show it too. Some say it’s a better way to see and capture the green flash (no flash!) because our eyes are better tuned at measuring the subtleties of light in the morning.

Owing to the vast number of cameras pointed at sunsets and sunrises around the world today, we can do online searches for images of the green flash (not a pulse either) and come up with lots of examples of it happening. There are even videos of it, showing it in real-time. You’ll be amazed at what you’ll see after watching it!

You’ll also come to understand why so many people are exposed to it every day and never even know it’s there!

So, there you go. The green flash seen at sunset is really real after all!

(But it’s not a flash!)

Originally published at http://ourevilveil.wordpress.com on January 21, 2023.