A modern celestial globe is covered over with figures from pole to pole, but the majority of these are of quite recent origin and belong to the Modern period of astronomy. They have been framed since the invention of the telescope, and since the progress of geographical discovery brought men to know the southern skies. If these modern constellations are cleared off, and only those of Aratus and Ptolemy suffered to remain, it becomes at once evident that the ancient astronomers were not acquainted with the entire heavens. For there is a large space in the south, left free from all the old constellations, and no explanation, why it should have been so left free, is so simple and satisfactory as the obvious one, that the ancient astronomers did not map out the stars in that region because they never saw them; those stars never rose above their horizon. [Illustration: THE ANCIENT CONSTELLATIONS SOUTH OF THE ECLIPTIC.] Thus at the present time the heavens for an observer in England are naturally divided into three parts, as shown in the accompanying diagram. In the north, round the pole-star are a number of constellations that never set; they wheel unceasingly around the pole. On every fine night we can see the Great Bear, the Little Bear, the Dragon, Cepheus and Cassiopeia. But the stars in the larger portion of the sky have their risings and settings, and the seasons in which they are visible or are withdrawn from sight. Thus we see Orion and the Pleiades and Sirius in the winter, not in the summer, but the Scorpion and Sagittarius in the summer. Similarly there is a third portion of the heavens which never comes within our range. We never see the Southern Cross, and hardly any star in the great constellation of the Ship, though these are very familiar to New Zealanders. [Illustration: THE CELESTIAL SPHERE. Zenith * * * * North Pole * * Stars / . * Always . Visible . / . Visible / . Hemisphere / . / . / . / . / (Earth surface) . / (Earth surface) South --------------------------------------- North / . Celestial / . / Equator Invisible . / . / Hemisphere . / . Stars / . Never . / Visible / South Pole