Besides those particular star-groups which lie behind the Sun as we journey there are many other constellations in all parts of the sky. Certain stars in the southern half of the heavens can be seen by people living on the northern half of our Earth. And certain stars in the northern half of the heavens can be seen by people living on the southern half of our Earth. But the very far north stars, lying over, or very nearly over, our north pole, are never seen at all in the far south of the Earth. And the very south stars, lying over, or very nearly over, our south pole, are never seen at all in the far north of the Earth. People living, for instance, in South Australia cannot get a glimpse of the Pole-star or the Great Bear; and people living in England or in New England cannot get a glimpse of the Southern Cross. Remember that, either way, whether from the north pole or from the south pole of the Earth, a man always looks _up_ into the sky. The heavens are always _upward_. The sky above the south pole is no more _downward_ than the sky above the north pole. All the “downward” of which we know is towards the centre or middle of our Earth. Nobody now need sit looking up at the sky and saying, “Twinkle, twinkle, little star; How I wonder what you are!” for we know what the stars are. I do not mean for a moment that we know all about them, or that we have not an immense amount still to learn. But we do certainly know what they are. They are _Suns_. The twinkling is not a part of the stars themselves. It is brought about by the way in which the little rays of star-light travel through our air. If we could get away from the Earth, right outside the air, we should then see the stars to shine steadily, without any twinkling. Jupiter and Venus and other planets do not twinkle when we look upon them. You may usually know a planet from a star by its not twinkling. No planet can ever be seen by us, even through the very biggest of telescopes, at such an enormous distance as that of the nearest star. For the planets shine by borrowed light, as our Moon shines; and you know how dim moonlight is, compared with sunlight. Only a sun, shining with the brilliance of its own great heat, can possibly be seen so very, very far away. Any number of worlds may be there: cooled worlds, like our Earth; half-cooled worlds, like Jupiter and Saturn--such worlds journeying round distant stars as the planets of the Solar System journey round our Sun. Only if they are there we cannot know it; our eyes cannot make them out. Suppose you and I could go for a long, long journey through the skies, straight from our Earth away to the star Alpha Centauri. That is the nearest star in all the heavens of which we yet know. Alpha Centauri is a very bright star, one of the First Magnitude. But you cannot see it in our northern skies. You would have to go much farther south to get a sight of Alpha Centauri.