6 April 2007

The Green Sun

Confused by the title? I'm not trying to make an April Fool here. We have indeed witnessed the Green Sun. This video of the setting Sun from a site atop Mt. Autore (altitude 1,850 meters) in Italy has captured a green flash while the Sun was setting. How can the Sun turn green? Why does it occur? When can we observe this phenomenon?

(The time between frames in the gif image above varies from over one minute in the beginning to about one second as the flash becomes visible. If the image is not changing try to refresh the page.)

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.

Picture of the Month - April 2007

Brilliant Venus, slender crescent Moon, and lights along the Ponte 25 de Abril, which is a 2.3 km long suspension bridge across Tagus river glow against the western twilight in this lovely Moonset scene from Lisbon, the capital city of Portugal, recorded on March 20, 2007. In fact, such serene views were enjoyed across planet Earth this week, as the young Moon remained near the setting Sun following a partial solar eclipse, and Venus ruled as the evening star. Because of strong Earthshine - light from the sunlit Earth - even the Moon's night side is clearly visible in the picture.