About each pole, as it happens to be turned earthward, is to be seen a round white patch (supposed to be snow), and this gradually disappears as the summer advances in that hemisphere of the planet—for Mars has seasons very closely resembling our seasons, except that they are about twice as long. The inclination of the axis of Mars to the plane of its orbit is about 24° 50′, which is not very different from the inclination of the earth's axis. Moreover, Mars rotates in a period of 24 hours, 37 min., 22 sec., so that the length of day and night upon its surface is very nearly the same as upon the earth. The surface of the planet is marked by broad irregular areas of contrasting colour, or tone, some of them being of a slightly reddish, or yellowish, hue, and others of a neutral dusky tint. The general resemblance to a globe of the earth, with differently shaped seas and oceans, is striking.