While Spirit has been stuck at Troy, it's been taking numerous opportunities to capture photos with dramatic twilight lighting. On sol 2,002 (three sols ago, or August 21), it gazed toward the setting Sun, snapping the shutter roughly once a minute.
NASA / JPL-Caltech / Cornell / animation and colorization by Peter Greutmann
A dusty sunset on Mars
While bogged down at Troy, Spirit looked westward on the evening of sol 2,002 to watch the Sun set. Before it reached the horizon, the Sun vanished into dust kicked up in a regional dust storm. This animation is composed of 11 Pancam frames captured over 12 minutes; they have been artificially colorized to add drama.
The Sun vanished from Spirit's view several minutes before it reached the horizon, because, as it says in the latest rover update, there's a bit of dust activity in Spirit's neighborhood just now: "Atmospheric conditions over Spirit have deteriorated owing to a regional dust storm. As of Sol 2001 (Aug. 19, 2009), the rover solar-array energy production was down to 744 watt-hours with atmospheric opacity (tau) increasing to 0.718 and the dust factor remaining around 0.8315." This is a relatively high tau but very much lower than the levels observed by both rovers during the global dust event two years ago. And it's a very nice dust factor, indicating Spirit's solar panels are still pretty clean. So don't be too concerned about the dust in the air -- it's mild as dust events go.