Where it sits
Real, photographable, and explained — with a mirage doing the work everyone credits to dispersion.
Tell it apart
| Aspect | Green flash | Blue flash |
|---|---|---|
| Refracted | Strongly | More strongly |
| Survives the path | Yes | Mostly scattered |
| Commonly seen | Yes | Rarely |
| Why | Last colour left | Removed en route |
Violet and blue are refracted even more than green, so by rights they should win. They lose to atmospheric extinction — over the long horizon path, scattering removes the shortest wavelengths almost completely, leaving green as the last colour standing.
What it doesn't mean
It's real physics. Sunset flashes have some physiological component from retinal bleaching, but they are not afterimages — and sunrise flashes, where no prior staring has occurred, are almost pure physics.
Dispersion alone produces a green rim ten times smaller than the naked eye can resolve. What makes it visible is magnification by a mirage — the same atmospheric temperature layering that produces mirages stretches the rim into something you can see. No mirage, no flash.
What it really means
The green flash has the profile of a tall tale — sailors, the last sliver of sun, a green blaze lasting a second, and an ancient legend about seeing into your own heart.
The legend part is fake, and traceably so: it was invented by a publisher to promote a Jules Verne novel. The flash is entirely real.
The standard explanation — atmospheric dispersion — is also only half of it, and this is the part most accounts skip. Air refracts short wavelengths more than long ones, so the sun's blue-green image sits fractionally higher than its red one and sets a second or two later, leaving a green rim at the very top edge. True, and insufficient: that rim is ten times smaller than the naked eye can resolve. By dispersion alone you would never see anything.
What makes it visible is a mirage. Temperature layering near the horizon magnifies the rim vertically, stretching a sliver you couldn't detect into a flash you can. No mirage, no green flash — which is why it isn't visible at every sunset despite dispersion happening at all of them.
One more piece of physics worth having. Violet and blue are bent more than green, so by rights they should be the last colours standing. They don't arrive at all: over the long, low, horizon-grazing path, scattering strips the shortest wavelengths out. Green wins by being the last colour still standing.
Where it comes from
English — plain description
The phenomenon has technically distinct sub-types — inferior-mirage flash, mock-mirage flash, sub-duct flash, green ray — so 'the green flash' is a popular umbrella over several different optical mechanisms.
- physics
Caused by atmospheric dispersion — refraction by air is stronger at shorter wavelengths, so the sun's blue-green image sets a second or two after its red one.
- the legend's actual origin
The romantic 'ancient Scottish legend' about seeing into one's true heart was invented by a publisher for a Jules Verne novel, not inherited folklore.
In real life
- Watching the last sliver of sun sink into a calm sea, you see its top edge turn emerald for a second or two before it disappears.
- It happens at sunrise too: from a hilltop with a clean distant horizon, the very first point of the rising sun can show green before it turns gold.
- Through a long lens, a photographer catches a thin green strip separating from the top of the setting sun and hanging there for a moment.
Questions
Q01Is the green flash real?
Yes. It's a documented optical phenomenon caused by atmospheric dispersion, made visible by mirage magnification. Sunrise flashes in particular are almost pure physics, since no prior staring at the sun has occurred to produce an afterimage.
Q02Why green rather than blue or violet?
Blue and violet are refracted even more strongly, so by rights they should be the last colours visible. But they're scattered out over the long low-angle horizon path, leaving green as the last colour still present when the sun's final rim disappears.
Q03Do you need an ocean horizon?
No — that's a documented fallacy. Green flashes occur almost everywhere, morning and evening. What you need is a clean distant horizon and the right atmospheric layering to produce the magnifying mirage.
Sources
- Explaining Green Flashes — San Diego State University.
- Fallacies about green flashes — San Diego State University.