The amazing image above of a sunset on exo-planet HD209458b 150 light years away, was reconstructed by Frederic Pont of the University of Exeter using data from a camera onboard the Hubble Space Telescope. Pont used his knowledge of how the color of light changes based on chemicals it encounters, and computer modeling, to create an actual image of what a sunset on the actual planet would look like. He’s posted it on his blog.
The light from Osiris’s star is white, like our own sun, but when it passes through the sodium in Osirisi’s atmosphere, red light in it is absorbed, leaving the starlight to appear blue. But as the sun sets, the blue light is scattered in the same way as it is here on Earth (Rayleigh scattering) causing a gradual change to green, and then to a dim dark green. And finally, due to diffraction, the bottom of the image becomes slightly flattened.