7 years of great love. When you see the Green flash during sunset. Well, that’s what they say about it. If you want a more scientific approach, read more what Wikipedia has to say about this.
Green flashes and green rays are optical phenomena that sometimes occur right after sunset or right before sunrise. When the conditions are right, a green spot is visible above the upper rim of the disk of the sun. The green appearance usually lasts for no more than a second or two. Sometimes (rarely) the green flash can resemble a green ray shooting up from the sunset (or sunrise) point. Green flashes occur because the atmosphere can cause the light from the sun to separate out into different colors.
Green flashes are enhanced by mirage, which increase refraction. A green flash is more likely to be seen in stable, clear air, when more of the light from the setting sun reaches the observer without being scattered. One might expect to see a blue flash, since blue light is refracted most of all, and the blue component of the sun’s light is therefore the very last to disappear below the horizon, but the blue is preferentially scattered out of the line of sight, and the remaining light ends up appearing green.