Mars-View Moons

Phobos measures 27 x 21 x 19 km, while Deimos is second 15 x 12 x 11 km.

Deimos is 20,000 km above the planet, while Phobos is 6100 km high.

Phobos has characteristics which suggest that it was once part of a larger celestial body

Despite being so close, these satellites are only visible in the Martian sky as bright points of light. The brightness of Deimos may be comparable to that of Venus seen from Earth; Phobos is several times brighter.

Phobos makes a complete orbit of Mars in 7 h 39 min 14 s. As it revolves much faster than the planet itself rotates, the satellite appears to be moving in a retrograde manner, from the west and to the east.

Deimos takes 30 h 17 min 55 s to orbit Mars. One complete revolution is, therefore, a little longer than the planet's rotation, which causes the satellite to move slowly in the sky. 64 hours pass between Deimos' rising in the east and its' setting in the West

Because these satellites are so close to Mar's surface and gravitate to its equatorial plane, they are invisible from Mars' polar regions.

Deimos cannot be seen from above the 82nd parallel and Phobos from latitudes above 69º.

Given their small size, these tiny moons do not do much to dispel the darkness of the Martian night. For short periods of time they gravitate away from the planet and equatorial orbits, spending most of the night hidden in the cone of shadow cast by the side of the planet that is not illuminated by sunlight.

Phobos' orbit has been observed to have been gradually changing. The orbit's secular acceleration is caused by Martian tides.

Observation of solar eclipses from Mars

NASA's Mars Exploration Rover Opportunity took the first photographs of solar eclipses by the moons of Mars in March 2004.

Phobos covers a larger part of the sun because it is larger than Deimos, and orbits closer to Mars. The eclipse of Deimos captured March 4, 2004 is comparable to a transit of a planet.