But the marks on the planet, though very faint, are still sufficiently definite to have enabled some sharp-sighted astronomers to answer a question of much interest. They have made it plain that in one most important respect Venus is very unlike our Earth. Our globe, of course, rotates on its axis once each day, but Venus requires no less than 225 days to complete each rotation. In fact, this planet rotates in such a fashion that she always keeps the same face to the sun. The inhabitants of Venus will therefore find that it is perennial day on one side of this globe and everlasting night on the other.
Venus is one of the few globes which might conceivably be the abode of beings not very widely different from ourselves. In one condition especially—namely, that of weight—she resembles the earth so closely that those bodies which we actually possess would probably be adapted, so far as strength is concerned, for a residence on the sister planet. Our present muscles would not be unnecessarily strong, as they would be on the moon, nor should we find them too weak, as they would certainly prove to be were we placed on one of the very heavy bodies of our system. Nor need the temperature of Venus be regarded as presenting any insuperable difficulties. She is, of course, nearer to the sun than we are, but then climate depends on other conditions besides nearness to the sun, so that the question as to whether Venus would be too hot for our abode could not be readily decided. The composition of the atmosphere surrounding the planet would be the most material point in deciding whether terrestrial beings could live there. I think it to be in the highest degree unlikely that the atmosphere of Venus should chance to suit us in the requisite particulars, and therefore I think there is not much likelihood that Venus is inhabited by any men, women, or children resembling those on this earth.
THE PLANET MARS AND HIS MOVEMENTS.
The path of the earth lies between the orbits of the planets Venus and Mars. It is natural for us to endeavor to learn what we can about our neighbors. We ought to know something, at all events, as to the people who live next door to us on each side. I have, however, already said that we cannot observe very much upon Venus. The case is very different with respect to Mars. He is a planet which we are fortunately enabled to study minutely, and he is full of interest when we examine him through a good telescope.
The right season for observing Mars must, of course, be awaited, as he is not always visible. Such seasons recur about every two years, and then for months together Mars will be a brilliant object in the skies every night. Nor has Mars necessarily to be sought in the early morn or immediately after sunset, in the manner we have already described for Venus and Mercury. At the time Mars is at his best he comes into the highest position at midnight, and he can generally be seen for hours before, and be followed for hours subsequently. You may, however, find some difficulty in recognizing him. You probably would not at first be able to distinguish Mars from a fixed star. No doubt this planet is a ruddy object, but some stars are also ruddy, and this is at the best a very insecure characteristic for identification. I cannot give you any more general directions, except that you should get your papa to point out Mars to you the next time it is visible. It is just conceivable that papa himself might not know how to find Mars. If so, the sooner he gets a set of star maps and begins to teach himself and to teach you, the better it will be for you both.
Mars, though apparently so like a star, differs in some essential points from any star in the sky. The stars proper are all fixed in the constellations, and they never change their relative positions. The groups which form the Great Bear or the Belt of Orion do not alter, they are just the same now as they were centuries ago. But the case is very different with a planet such as Mars. The very word planet means a wanderer, and it is justly applied, because Mars, instead of staying permanently in any one constellation, goes constantly roaming from one group to the other. He is a very restless body; sometimes he pays his respects to the heavenly Twins, and is found near Castor and Pollux in Gemini, then he goes off and has a brief sojourn with the Bull, but it looks as if that fierce animal got tired of his company and hunted him off to the Lion. His quarters then become still more critical. Sometimes it looks as if he desired to seek for peace beneath the waters, and so he visits Aquarius, while at other times he is found in dangerous proximity to the claws of the Crab.
Mars cannot even make up his mind to run steadily round the heavens in one direction; sometimes he will bolt off rapidly, then pause for a while, and turn back again; then the original impulse will return, and he will resume his journey in the direction he at first intended. It is no wonder that I am not able to give you very explicit directions as to how you may secure a sight of a truant whose wanderings are apparently so uncertain. Yet there is a definite order underlying all his movements. Astronomers, who make it their business to study the movements of Mars, can follow him on his way; they know exactly where he is now, and where he will be every night for years and years to come. The people who make the almanacs come to the astronomers and get hints from them as to what Mars intends to do, so that the almanacs announce the positions in which the planet will be found with as much regularity as if he was in the habit of behaving with the orderly propriety of the sun or the moon.
We must not lay all the blame on Mars for the eccentricities of his movements. Our earth is to a very large extent responsible. What we think to be Mars’ vagaries are often to be explained by the fact that we ourselves on the earth are rapidly shifting about and altering our point of view.
Fig. 52.—How the Tree seems to move about.