Tiny sun rises on the horizon of a Martian plain. A robotic arm is visible in the foreground.

Sunset at Gusev Crater: The Sun sinks below the horizon in this stunning panoramic view captured by NASA's Spirit Mars rover in 2005. NASA/JPL/Texas A&M/Cornell | › Full image and caption

NASA's Viking 1 lander first showed humans what a sunset looked like on Mars in 1976. Several more Red Planet robots have since sent back a variety of views of Martian sunrises and sunsets.

Some color-corrected, blue-hued images preview what human Mars explorers might one day see while relaxing after a hard day's work on the fourth planet:

Rocky red landscape in fading light.
First Twilight: This Viking 1 image is one of first images of a sunset as seen from the surface of Mars. Credit: NASA/JPL/LaRC | › Full image and caption

Because Mars is farther from the Sun than Earth, the Sun appears only about two-thirds the size we see when we watch sunsets here on Earth.

Why is Mars Red? Why Are Some Images Blue?

Mars is known as the Red Planet because of iron oxide (like rust) in its soil. The planet's distinctive reddish hue is visible from Earth even without the aid of a telescope. The ancient Romans named it for their God of War (Ares in Greek mythology).

So what's with the blue twilight?

Just as colors are made more dramatic in sunsets on Earth, Martian sunsets would appear bluish to human observers watching from the red planet. Fine dust makes the blue near the Sun's part of the sky much more prominent, while normal daylight makes the Red Planet's familiar rusty dust color more prominent.

"The colors come from the fact that the very fine dust is the right size so that blue light penetrates the atmosphere slightly more efficiently," said Mark Lemmon of Texas A&M University, College Station, a science team member of the Curiosity rover mission. "When the blue light scatters off the dust, it stays closer to the direction of the Sun than light of other colors does. The rest of the sky is yellow to orange, as yellow and red light scatter all over the sky instead of being absorbed or staying close to the Sun."

Science Behind the Scenery

These images are more than just beauty shots.

Martian sunset and twilight images help scientists determine how high into the atmosphere the martian dust extends, and allow them to look for dust or ice clouds.

Other images have shown that the twilight glow remains visible, but increasingly fainter, for up to two hours before sunrise or after sunset. The long martian twilight (compared to Earth's) is caused by sunlight scattered around to the night side of the planet by abundant high altitude dust.

Similar long twilights or extra-colorful sunrises and sunsets sometimes occur on Earth when tiny dust grains that are erupted from powerful volcanoes scatter light high in the atmosphere.

Read More

Viking 1 In Depth

Viking 2 In Depth

Spirit Mars Rover In Depth

Curiosity Mars Rover In Depth

Insight Lander In Depth

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