This one has been making the rounds on a few blogs, and it IS pretty cool.

“On May 19, 2005, NASA’s Mars Exploration Rover Spirit captured this
stunning view as the Sun sank below the rim of Gusev crater on Mars.
This Panoramic Camera mosaic was taken around 6:07 in the evening of
the rover’s 489th Martian day, or sol.

Sunset and twilight
images are occasionally acquired by the science team to determine how
high into the atmosphere the Martian dust extends, and 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.”

Image Credit: NASA/JPL/Texas A&M/Cornell”
http://www.nasa.gov/multimedia/imagegallery/image_feature_347.html