Mars is, famously, The Red Planet. The rust in the dust on its surface gives the surface a reddish-brown appearance. It vast dry, dusty expanses call to mind Earthlike deserts, in which a red-orange sun beats down on yellow sand. As a result, when we think of a Mars sunset, most think of it as blazing red.
Footage released by NASA shows us the exact opposite. The sun glows a cool blue as it sets in the Martian sky. It’s quite an upset of perception, and it’s all due to that famous red dust.
On Earth, the particles in the atmosphere scatter blue light. When a ray of light hits them, the blue wavelengths are diverted from their course and shot randomly outwards. As it moves out, it hits other air particles, and some of it scatters down to the surface of the Earth. Those standing on the surface look up into the sky, see the light that’s scattered down, and say the sky is blue. Meanwhile, direct light from the sun has had all the blue wavelengths filtered out; they’ve been scattered all over the sky. This leaves only the wavelengths at the reddish end of the spectrum – so when people look at the sun, they see it as yellow. Towards sunset, they’re looking at the sun through more filtering atmosphere, and so it grows more intensely red-yellow.
On Mars, exactly the opposite happens. The red dust in the atmosphere scatters red light, so when anyone looking around would see a reddish sky. Meanwhile, the red wavelengths are filtered out of the direct path of light from the sun, leaving light towards the bluish end of the color spectrum. Those looking at the sun will see it as blue. And very seasonal.
