Fig. 63.—Mars and his Two Satellites.
In Number One there lives an old bachelor, and in Number Two a single lady. These are Mercury and Venus, and of course there are no children in either of these houses. Number Three is inhabited by old mother Earth, and she has got a fine big son, called the Moon. Number Four is a nice little house inhabited by Mars. There are to be found a pair of little twins, and nimble creatures they are too. Number Five is a great mansion. A very big man lives here, called Jupiter, with four robust sons and daughters that everybody knows. I fancy they must go to many dancing parties, for every night they may be seen whirling round and round. For three hundred years these four moons have been known to astronomers, but in 1892 there was an addition to the family in the shape of a tiny moon which had never been seen up to that time. Number Six is also a fine big house, though not quite so big as Number Five, but larger than any of the others. It is inhabited by Saturn, and contains the biggest family of all. Up till the other day eight sons and daughters were known to live here, but they are not nearly so sturdy as Jupiter’s children; in fact, the young Saturns do not make much display, and some of them are so delicate that they are hardly ever seen. In this household, too, a new member has recently appeared. For fifty years the family was known to consist of these eight sons and daughters, but in August, 1898, when they were being photographed in a group, it was discovered that a ninth moon had been added. Number Seven is also a fine large house; but Uranus, who lives there, is such a recluse that unless you carefully keep your eye on his house, you will hardly ever catch a glimpse of him. There are four children in that house, I believe, but we hardly know them. They move in circles of their own, and apparently have seen a good deal of trouble. Only one more house is to be mentioned, and that is Number Eight, inhabited by Neptune. It contains one child, but we are hardly on visiting terms with this household, and we know next to nothing about it.
Before 1877, Mars appeared to be in the same condition as Venus or Mercury—that is, devoid of the dignity of attendants. There was, however, good reason for thinking that there might be some satellites to Mars, only that we had not seen them. You see that, as Number Three had one child, and Numbers Five, Six, Seven, and Eight had each one, or more than one, it seemed hard that poor Number Four should have none at all. It was, however, certain that if there were any satellites to Mars, they must be comparatively small things; for if Mars had even one considerable moon, it must have been discovered long ago.
On the memorable occasion in 1877, Professor Hall discovered that the ruddy planet Mars was attended, not alone by one moon, but by two. Their behavior was most extraordinary. It appeared to him at first almost as if one of these little moons was playing at hide-and-seek. Sometimes it would peep out at one side of the planet, and sometimes at the other side. I have here a picture ([Fig. 63]) which shows how these moons of Mars revolve. That is the globe of the planet himself in the middle, and he is turning round steadily in a period which is nearly the same as our day. But the remarkable point is that the inner of the moons of Mars runs round the planet in 7 hours 39 minutes. It would seem very strange in our sky if we had a little moon which rose in the west instead of in the east, and which galloped right across the heavens three times every day—and this is what Mars has. The outer moon takes a more leisurely journey, for he requires 30 hours 18 minutes to complete a circuit. If for no other reason than to see these wonderful moons, it would be very interesting to visit Mars.
The satellites of this planet are in contrast to our moon. In the first place, our moon takes 27 days to go round the earth, and is comparatively a long way off. The moons of Mars are much nearer to their planet, and they go round much more quickly. There is also another difference. The moons of Mars are much smaller bodies than our moon. If we represent Mars by a good-sized football, his moons, on the same scale, would be hardly so big as the smallest-sized grains of shot. Does it not speak well for the power of telescopes in these modern days that objects so small as the satellites of Mars should be seen at all? You remember, of course, that neither Mars himself nor his moons have any light of their own. They shine solely in consequence of the sunlight which falls upon them. They are merely lighted like the earth itself, or like the moon. The difficulty about observing the satellites is all the greater because they are seen in the telescope close to such a brilliant body as Mars. The glare from the bright planet is such that when we want to see faint objects like the satellites we have to hide Mars, so as to get a comparatively dark space in which to search.
Now that they know exactly what to look for, a good many astronomers have observed the satellites of Mars. A superb telescope is nevertheless required. And, in fact, you could not find a better test for the excellence of an instrument than to try if it will show these delicate objects. But do not imagine that merely having a good telescope and a clear sky is all that is requisite for making astronomical discoveries. You might just as well say that by putting a first-rate cricket-bat in any man’s hands will ensure his making a grand score. Every boy knows that the bat does not make the cricketer, and I can assure him that neither will the telescope make the astronomer. In both cases, no doubt, there is some element of luck. But of this you may be certain: that as it is the man that makes the score, and not the bat, so it is the astronomer that makes the discovery, and not his telescope.
Deimos and Phobos were the names of the two personages, according to Homer, whose duty it was to attend on the god Mars, and to yoke his steeds. A conclave of classical scholars and astronomers appropriately decided that Deimos and Phobos must be the names of the two satellites to the planet which bears the name of Mars.
HOW THE TELESCOPE AIDS IN VIEWING FAINT OBJECTS.
We have been hitherto talking about large planets, which, if not as big as our earth, are at least as big as our moon. But now we have to say a few words about a number of little planets, many of them being so very small that a million rolled together would not form a globe so big as this earth. These little objects you cannot see with your unaided eye, and even with a telescope they only look like very small stars.