Dark spots on the Sun are very often to be seen; sometimes only through a telescope, but now and then one is large enough to be seen with no such help--by the eye alone. It was by means of these spots that the Sun was first found to spin upon its axis, just as our Earth does. A black spot would be noticed upon one side of the Sun’s face. It would be seen slowly to cross over, and to disappear on the other side. Nearly a fortnight would be needed for the journey across, and for another fortnight, or nearly so, the spot would be hidden behind the Sun. After which it would turn up again, on the same side as at first, and in the very same place. Then once more it would travel across and disappear, and in another fortnight it would come round over to its starting-point. If only a single spot had behaved in this way it might have meant little. But when numbers of spots did the very same thing, time after time, it became clear that the great body of the sun was whirling round, carrying the spots with it. The Sun, like the Earth, has a north pole, and a south pole, and an equator. We give the name “north pole” to one end of the axis or line on which he spins, and the name “south pole” to the other end of that axis. And we give the name “equator” to a line exactly round the middle of the Sun, half-way between his two poles. Most of the spots which we see are somewhere near the Sun’s equator, not very near to his north pole or to his south pole. They come and go and change their shapes, and get bigger or smaller--sometimes slowly, sometimes very fast. A spot may appear and grow and vanish again in one day, or it may stay on for days and weeks, and even months, hardly altering at all, only journeying round and round the Sun. These things show us that the great Sun spins round upon his axis: and that for each spin he takes about twenty-five or twenty-six days. But the whirling round of the Sun means no Day and Night by turns to him, for the whole of the Sun is always light--bright with his own radiance. Once upon a time it used to be thought that the Sun spots were perhaps _raised_ things--dark objects standing high, like mountains. And I will tell you why this idea was given up. Take an empty cup, and hold it before your eyes, with the open part turned full towards you. The cup must be held as if lying on its side--not with the mouth upwards, as it would stand on a table. You can see, thus, the full circle of the opening, and the whole empty inside. Next, move it a little way to the right from before your face, turning it slightly away, and you will then see no longer the whole inside, but only a part: and the round opening will have an oval look. Turn it still further, and you will see a very narrow oval opening, and hardly any of the inside. Now this is just how the spots seem to behave as they cross the Sun.