14. Why should we see a star if we cannot see a planet at that distance? A star shines by its own light. A planet shines only by reflected light, therefore much more dimly. 15. If we could journey to the nearest known star, how much should we see of the Solar System? No planets nor moon at all: nothing but the Sun as one dim star. CHAPTER XXII. GIANT-SUNS AND CLUSTERS. All stars do not shine alike. They are different in brightness, different in size, different in speed. There are brilliant suns and dim suns, great suns and little suns, fast suns and slow suns, in the universe of stars, just as there are brilliant worlds and dim worlds, great worlds and little worlds, fast worlds and slow worlds, in our Solar System. But the brightest star is not always truly the biggest star; just as the brightest planet in our sky is by no means always the largest world. You know how bright Venus is--a good deal brighter than Jupiter. Yet Venus is far, far smaller than Jupiter. Venus is brighter because she is so much the nearer of the two, not at all because of greater size. The very brightest star in our whole sky is SIRIUS. Yet you must not suppose that Sirius is larger in himself than any other star. He is brighter partly because he is so much _nearer_ than most other stars. I do not mean to say that Sirius is what one would call a very near star, if such a word can be used about any single star in the sky. Alpha Centauri, though the nearest of which we know, is not really near; and Sirius is perhaps nearly twice as far off as Alpha. That, however, is not much, compared with the enormous distances of many stars. Sirius is no doubt a splendid Sun, most likely larger and brighter than our Sun. But our Sun is not so very particularly large as a star among stars. He is only large as a Sun among little worlds. Sirius may very well be bigger than our Sun and yet be by no means one of the biggest stars in the sky. No one has yet been able to measure the actual size of Sirius, because he always looks to us like one point of light. But we know about how far off he is, and we know that our Sun at that same distance would not be so bright a star as Sirius is. This looks as though Sirius were the larger Sun of the two, only without any very startling difference. Matters are otherwise when we turn to ARCTURUS. Sirius is in the southern half of the heavens, and Arcturus is perhaps the very brightest star in all the northern half of the heavens, though a good way behind Sirius in radiance. Arcturus seems to be a truly wonderful Sun. He is eleven millions of times farther away from us than our Sun is. Imagine what this means! If you had a rope 92 millions of miles long, reaching from our Earth to the Sun, you would need _eleven millions_ of such ropes, joined end to end, to reach from the Earth to Arcturus!