The seven stars of Charles's Wain, showing the directions in which they are travelling. (After Proctor.)
There is another very interesting fact known to us about Charles's Wain which I should like you to remember when you look at it. This is that the seven stars are travelling onwards in the sky, and not all in the same direction. It was already suspected centuries ago that, besides the apparent motion of all the stars in the heavens caused by our own movements, they have each also a real motion and are travelling in space, though they are so inconceivably far off that we do not notice it. It has now been proved, by very accurate observations with powerful instruments, that three of the stars forming the waggon and the two horses nearest to it, together with Jack, are drifting forwards (see Fig. 60), while the top star of the tailboard of the waggon and the leader of the horses are drifting the other way. Thus, thousands of years hence Charles's Wain will most likely have quite altered its shape, though so very slowly that each generation will think it is unchanged.
One more experiment with Charles's Wain, before we leave it, will help you to imagine the endless millions of stars which fill the universe. Look up at the waggon and try to count how many stars you can see inside it with the naked eye. You may, if your eye is keen, be able to count twelve. Now take an opera-glass and the twelve become two hundred. With your telescopes they will increase again in number. In my telescope upstairs the two hundred become hundreds, while in one of the giant telescopes, such as Lord Rosse's in Ireland, or the great telescope at Washington in the United States, thousands of stars are brought into view within that four-sided space!
Now this part of the sky is not fuller of stars than many others; yet at first, looking up as any one might on a clear evening, we thought only twelve were there. Cast your eyes all round the heavens. On a clear night like this you may perhaps, with the naked eye, have in view about 3000 stars; then consider that a powerful telescope can multiply these by thousands upon thousands, so that we can reckon about 20,000,000 where you see only 3000. If you add to these the stars that rise later at night, and those of the southern hemisphere which never rise in our latitude, you would have in all about 50,000,000 stars, which we are able to see from our tiny world through our most powerful telescopes.
But we can go farther yet. When our telescopes fail, we turn to our other magic seer, the photographic camera, and trapping rays of light from stars invisible in the most powerful telescope, make them print their image on the photographic plate, and at once our numbers are so enormously increased that if we could photograph the whole of the heavens as visible from our earth, we should have impressions of at least 170,000,000 stars!
These numbers are so difficult to grasp that we had better pass on to something easier, and our next step brings us to the one star in the heavens which never appears to move, as our world turns. To find it we have only to draw a line upwards through the two stars in the tailboard of the waggon and on into space. Indeed these two stars are called "the Pointers," because a line prolonged onwards from them will, with a very slight curve, bring us to the "Pole-star" (see Fig. 58). This star, though not one of the largest, is important, because it is very near that spot in the sky towards which the North Pole of our earth points. The consequence is, that though all the other stars appear to move in a circle round the heavens, and to be in different places at different seasons, this star remains always in the same place, only appearing to describe a very tiny circle in the sky round the exact spot to which our North Pole points.
Month after month and year after year it shines exactly over that thatched cottage yonder, which you see now immediately below it; and wherever you are in the northern hemisphere, if you once note a certain tree, or chimney, or steeple which points upwards to the Pole-star, it will guide you to it at any hour on any night of the year, though the other constellations will be now on one side, now on the other side of it.
The Pole-star is really the front horse of a small imitation of Charles's Wain, which, however, has never been called by any special name, but only part of the "Little Bear." Those two hind stars of the tiny waggon, which are so much the brightest, are called the "Guards," because they appear to move in a circle round the Pole-star night after night and year after year like sentries.
Fig. 61.
