What Causes The Green Flash At Sunset?


Many have marveled at the stunning sight of the green flash that sometimes appears just as the sun dips below the horizon during sunset. This optical phenomenon occurs when the sunlight is bent, or refracted, as it passes through the Earth’s atmosphere, causing the green light to be momentarily visible.

Physics Behind the Green Flash:

The green flash is a result of atmospheric refraction, specifically the dispersion of light. When the sun is setting, its light passes through a greater thickness of the Earth’s atmosphere, which causes the shorter wavelength colors, like green and blue, to scatter more than the longer wavelengths. The dispersion of light is more pronounced during the sunset and sunrise due to the oblique angle at which the sunlight passes through the atmosphere, leading to the separation of colors.

Conditions for Observing the Green Flash:

In order to witness the green flash, specific atmospheric conditions need to be in place. A clear, unobstructed horizon and stable air layers are essential for the light to refract properly and produce the green flash effect. The layers of air must have minimal turbulence to prevent distortion of the light as it travels through the atmosphere. Additionally, weather conditions such as low humidity and minimal cloud cover can enhance the visibility of the green flash.

Geographical Factors:

Different geographical locations may yield varying degrees of success in observing the green flash. Coastal regions, where the horizon is unbroken and the air is relatively stable, are prime spots for catching a glimpse of this natural spectacle. The proximity to large bodies of water can also influence the visibility of the green flash, as the water surface can act as a mirror, reflecting and enhancing the effect. In mountainous regions or areas with significant atmospheric disturbances, the likelihood of witnessing the green flash diminishes due to the presence of uneven terrain and turbulent air currents.

Elena Mars

Elena writes part-time for the Scientific Origin, focusing mostly on health-related issues.