THE SATELLITES OF MARS
Mars has a little family of two moons. Tiny little bodies they are, the smallest in the solar family except, perhaps, an occasional asteroid. Neither one of them is more than ten miles in diameter, and the two together are smaller than any other known satellite. They can only be seen when Mars is in opposition, and then only with a fairly large telescope. They were discovered in 1877, and named Phobos and Deimos, the names of the two attendants of the god of war. Phobos is the brighter and the nearer to the planet. It is less than four thousand miles from the surface of Mars; and on account of its being so near and the shape of Mars being a spheroid, like that of the earth, the little satellite can never be seen from Mars beyond sixty-nine degrees of latitude on each side of the equator. Within these limits it shows great activity. It makes a complete circuit around Mars in seven and a half hours; and this swift revolution, combined with the motion of Mars on its axis, makes Phobos seem to rise in the west and set in the east, pass over the heavens in less than twelve hours, and go through all its phases, from “new” to “full,” one and a half times every night. Its light is rather insignificant, being about sixty times less than we receive from our satellite; but, on the whole, it must be a rather gay and pleasant little moon.
Deimos is not any larger than Phobos, and not as bright; but it is slightly less difficult for us to see, because it is between two and three times farther away from Mars than Phobos is, and thus not so much lost in the light of the planet. It circles around Mars in a little more than thirty hours, and this, being only six hours more than Mars consumes in turning around on its axis, results in requiring more than two days for the satellite to pass from rising to setting. Between rising and setting it goes through its phases four times. It can be seen from all parts of Mars, but gives very little light to the planet—more than a thousand times less than our moon gives us.
The symbol of Mars is ♂, a conventionalized figure representing a shield and a spear—implements of war appropriate for the use of the deity especially connected with warfare.