For reference, this is what the daytime sky looked like on Mars through a self-portrait Curiosity took with another camera mounted on its robotic arm:
The intensity of the sunset's blueness is explained by the same principles at work to make a vivid Earth sunset, just with different colors. Light from a setting sun has to pass through the atmosphere on a longer path than it does at mid-day, NASA explains.
The blue color seen in the photographs is close, but not identical, to what a human on Mars would see while taking some time out of a busy day working on Mars to watch the sun set. If anything, NASA says, the MastCam's lens is "actually a little less sensitive to blue than people are."
The photographs were sent home on April 15, from the rover's position in the Gale Crater. The images returned to Earth from Curiosity's MastCam are in black and white but contain coded information that, when decoded, reveals color. Some, like Damia Bouic, were able to decode the colors contained within the image on their own. NASA released its own color image sequence on Friday.
Curiosity's sunset sequence follows in the footsteps -- or, more accurately, tire marks -- of its older sibling Opportunity, which captured this sunset in 2010:
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