This stunning image of a Martian sunset was captured by the Mars Exploration Rover Spirit on May 19, 2005. Sunset colors on Mars are opposite of what is usually seen on Earth. On Mars, the sky is red and the setting Sun appears blue. The blue color is caused by dust scattering the light just as it does on Earth. This blue color is caused iron oxide dust particles in the atmosphere scattering the the sunlight.
NASA / JPL / National Solar Observatory / Sacramento Peak