Sunsets on Mars are blue

1On Earth, sunsets glow red; on Mars it is the reverse — a hazy blue-grey ring around the setting Sun. In 2015 NASA's Curiosity rover photographed just such a sunset on the Martian surface.

2The physics is the same as Earth's: incoming sunlight scattered by the atmosphere. But Mars's air is full of fine dust that scatters red light strongly, leaving blue light concentrated near the Sun — the exact opposite of Earth's air molecules, which scatter blue light across the whole sky (blue days, red sunsets).

3One more difference: the Sun looks much smaller from Mars. Because Mars orbits farther out, the Sun's apparent size is only about two-thirds of what we see from Earth.