Transit Transit of Phobos from Mars

video (01:30/real-time): eclipse of sun phobos, largest of 2 moons of mars (curiosity rover, 20 august 2013).

a transit of phobos mars lasts thirty seconds or so, due moon s rapid orbital period of 7.6 hours.

because phobos orbits close mars , in line equator, transits of phobos occur somewhere on mars on days of martian year. orbital inclination 1.08°, latitude of shadow projected onto martian surface shows seasonal variation, moving 70.4°s 70.4°n , again on course of martian year. phobos close mars not visible south of 70.4°s or north of 70.4°n; days in year, shadow misses surface entirely , falls north or south of mars.

at given geographical location on surface of mars, there 2 intervals in martian year when shadow of phobos or deimos passing through latitude. during each such interval, half dozen transits of phobos can seen observers @ geographical location (compared 0 or 1 transits of deimos). transits of phobos happen during martian autumn , winter in respective hemisphere; close equator happen around autumnal equinox , vernal equinox, while farther equator happen closer winter solstice.

observers @ high latitudes (but less 70.4°) see noticeably smaller angular diameter phobos because considerably farther away observers @ mars s equator. result, transits of phobos such observers cover less of sun s disk. because orbits close mars, phobos cannot seen north of 70.4°n or south of 70.4°s; observers @ such latitudes not see transits, either.

mars rover opportunity rover photographed transits of phobos on 7, 10 , 12 march 2004. in captions below, first row shows earth time utc , second row shows martian local solar time.

the data in tables below generated using jpl horizons. there small discrepancy times reported series of images above. may due imprecision in ephemeris data used jpl horizons; jpl horizons data gives local apparent solar time while times reported above form of mean solar time (and therefore of discrepancy due martian equivalent of equation of time).