For an entire Martian year (or in Earth-time, July 16, 2006 - June 8, 2008), Opportunity snapped a picture of the sun's position in the sky every third day at 11:02 a.m. The result? This tracing of the teardrop-shaped path the sun follows in Mars' sky.

The path of the sun's fluctuating movement through the course of an entire year is called an analemma—and you can see the same phenomenon here on Earth. But, in our own sky, the sun does a figure-eight instead. The difference can be attributed to Mars' elliptical orbit, with the pointy end of the analemma occurring when Mars is furthest from the sun.

Image: NASA/JPL/Cornell/ASU/TAMU via APOD