Page:Mars - Lowell.djvu/46

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period, the difference amounts to 74 days. In one hemisphere winter is long and cold, summer short and hot; in the other winter and summer interchange. Owing to the present position of the line of apsides, the line connecting the points of Mars’ nearest approach to and farthest recession from the Sun, the former hemisphere happens to be the southern one; the latter, the northern. The lengths of their respective seasons are as follows:—

In the northern hemisphere, winter lasts 147 of his own days; spring, 191 days; summer, 181 days; autumn, 149 days; while in the southern hemisphere, winter lasts 181 days; spring, 149 days; summer, 147 days; autumn, 191 days.

Curiously enough, an analogous distribution of heat and cold occurs also at the present time in the case of the Earth; its axis and line of apsides holding the same relation to each other that the Martian ones do. This similarity of aspect is, as we shall see later, apparently very curiously reproduced in certain peculiarities of the surfaces of the two planets. But with Mars the result is much more marked on account of the greater eccentricity of his orbit, which is .0931 as against the Earth’s .0168.

As even under these exaggerated conditions his two polar regions show much alike, modern theories about our glacial epochs are considerably shaken.