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A Martian day lasts almost identical to that of a day on Earth: 24.5 hours. The sun rises from the east and sets in the west, as on our planet. But there is a big difference: on Mars the sunrises and sunsets are blue.
On Earth, the molecules of the gases in the atmosphere scatter the blue light, this phenomenon is called Rayleigh Scattering. At sunrise and sunset direct sunlight crosses the maximum atmospheric thickness and reaches us so impoverished in short wavelengths that we see the solar disk and the nearby sky red or orange. But most of our sky stays blue all day long.
On Mars things are a little different. Its atmosphere has only 1% of the Earth's atmosphere density and the amount of Rayleigh scattering is much less. The daytime sky of Mars would be rather black, like that on the Moon. But Martian dust forms an aerosol that disperses long wavelengths by Mie scattering, because dust particles are much larger than gas molecules, and absorbs blue light. This is why the Martian sky during most of the day is yellowish or reddish brown. Part of the blue light is also scattered, but at very slight angles. Therefore the blue light is deflected less than longer wavelengths. At sunrise and sunset, when the Sun is seen through the maximum thickness of the dusty Martian atmosphere, the amount of Mie scattering is amplified and this gives Mars a brief blue moment, a beautiful aureole of scattered blue light surrounding the solar disk.

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Comment by Joan J. Silvestre Bataller on January 3, 2018 at 5:10pm

I am very pleased that International space art network is working again and to be able to share my work with all of you. Many thanks to John E. Kaufmann and Nick Stevens for maintaining this site.

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