It is quite difficult to observe the Green Flash. It usually occurs during sunrise or sunset. This phenomenon is caused by the atmospheric bending or refraction of sunlight. Like a weak prism, the Earth's atmosphere breaks white sunlight into the seven colours, bending red colours slightly and green and blue colours through increasingly larger angles. When the sky is clear, a green flash just above the Sun's edge can sometimes be seen for a second or so, when the Sun is close to the horizon.
The above image was taken at the western horizon of Madagascar
This image of Green Flash was taken at the La Silla Observatory, in Chile, on October 15, 2005. The sun has almost set behind the mountain ranges of the western Chile when the Green Flash was observed.
Note: Click on the pictures for a better view.