High-phase Phobos and Deimos mutual event from Mars Express
This 131-frame animation documents a "mutual event" of Phobos and Deimos -- the two appeared to pass by each other as the Mars Express orbiter moved along its own path.
The original images have been aligned to hold the vertical position of Deimos constant. In the raw image data, the moons bob up and down as Mars Express adjusts its pointing:
ESA / DLR / FU Berlin (G. Neukum) / Emily Lakdawalla
Phobos and Deimos mutual event from Mars Express (raw)
Geometry of the Mars Express Phobos and Deimos mutual event
On November 5, 2009 at 08:14 UTC, the moons of Mars happened to be aligned just right as Mars Express crossed Mars' equator on its polar orbit for the orbiter to capture images of Phobos and Deimos together in the sky.