Martian sunset at Gusev crater. Mars has long twilights because high in the atmosphere there is a lot of dust reflecting the glow of sunlight. Volcanic dust can do this on Earth too. The color in this image - taken by the rover Spirit - was adjusted to approximate what human eyes might see. (Credit: NASA/JPL/Texas A/Cornell)  ©Mona Evans, “Mars Facts for Kids” http://www.bellaonline.com/articles/art36393.asp