Earth and Mars are a bit like mirror worlds. Mars is the Red Planet. Earth is the pale blue dot. Mars is a frigid desert. Earth is full of water and life. But there's another paradoxical difference. The sky on Mars is red, while its sunsets are blue.

The reason behind this is similar to why the Earth's sky is blue and the sunsets are red. The light from the Sun scatters based on what is in the atmosphere. Sunlight comprises light of many different wavelengths, and molecules and dust particles only interact with specific waves. The scattering of light by these particles is key to the color that is visible.

Mars’ atmosphere is very tenuous; its pressure is equivalent to about 1 percent of Earth’s. It is made of carbon dioxide and has a lot of dust. This fine dust tends to scatter red light so that the sky appears reddish, which lets the blue light through. On Earth, it is the opposite. Blue light bounces off air molecules giving the sky its characteristic hue.

During the sunset light has a longer distance to travel within the atmosphere, so it scatters more. What is left is the blue hue. On Earth, there is a wider palette of reds, which is amplified by ash from volcanoes, dust from fires and pollution. On Mars, the 'atmosphere' has a cool blue hue.

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