Green flash |
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At sunrise or sunset the rim of the Sun may appear for a second or so to be a bright green. The effect is due to dispersion in the atmosphere associated with refraction in density gradients. A long uniform path length is required. The most common sighting is over the sea at sunset. The full range of refraction effects are seen in the simulation. The image of the round disc is flattened with red below. The flattened image sinks towards the horizon. An 'hourglass' mirage develops. The image on the horizon appears to be square. The final flash is bright green. The simulation was made with a tank containing a salt water gradient. Dipersion in a refractive index gradient. |