Are mars moons visible at the same time on the surface of the planet?
They can be. But not all the time. First, you have to be relatively close to the equator (the satellites are smaller than our Moon and are on much closer orbits, so if you are too far away from the equator, they might not rise above the horizon). Then you have to watch for Phobos rising in the West! and moving towards the East. Phobos is so low that it orbits in a little over 7 hours. Because it is so close, you would actually note a difference in its apparent size as it rises above the horizon (when it passes directly overhead, it would be much closer than when it rises). During the day, it would often pass in front of the Sun if you are at the right place (in fact, Opportunity took a picture of Phobos passing in front of the Sun). Deimos is much smaller and further out. It would appear as a star (except, of course, it would move against the background of fixed stars — a bit like an artificial satellite as seen from Earth).
