One Martian Moon Passes the Other
This video depicts NASA’s Curiosity rover observing Mars’ two moons, then shows one moon passing in front of the other.
Both moons orbit in the same direction that Mars rotates. However, Phobos orbits Mars in less than a Martian day, which means it’s orbiting faster than the planet rotates, and thus rises in the West & sets in the East. Deimos is like our own Moon & takes longer than a Martian day to orbit, so Mars rotates quicker than Deimos orbits, and thus Deimos rises in the East & sets in the West.