The explanation is that the point which they passed with so great an effort is the exact centre of the world; they are now on its further side, and above them is the other hemisphere, where all is ocean save the island of Purgatory. Virgil explains how it was through the fall of Lucifer from Heaven that all the land except Purgatory is in one hemisphere, and that there is a cavity through which they may now climb to the opposite hemisphere. When Lucifer fell, all the land which then existed in the unknown hemisphere fled for fear of him, sinking under the sea, and then escaping round the globe settled in the inhabited hemisphere. It may be, he adds, that then the earth in the interior fled away from him upwards to form land in this hemisphere (Purgatory) and thus an empty space is left here. Up this, which is the same length as the tunnel of the Inferno, they climb, guided through the darkness by the sound of a little brook which has worn its winding way down the rock. On this route there is nothing to detain them, for they are alone in the darkness, but it presumably takes much longer to ascend than it did to descend, for climbing without a pause it takes about twenty-three hours (from the centre) to reach that round hole in the rocks through which at last they once more see the stars, just before the dawn of a new day. 3. PURGATORY. Leaving Earth’s centre at sunset by Jerusalem time, sunrise by Purgatory time, the poets emerge next morning by starlight when the morning star is making all the orient smile. Henceforth Dante does not need to be told how moon or stars are standing in the sky: he has but to look up, and see the sun and sometimes the moon by day, the stars and sometimes the moon by night. The Inferno was like one long dark night, Paradise will be one brilliant day; in Purgatory the sun rises four times and sets three times, before Dante reaches the summit, and thence rises to Paradise with Beatrice. “Lo bel pianeta che ad amar conforta”[461] is of course Venus: if there were any doubt about this, the words used concerning the dawn of the last morning on the Mountain would solve it, for there “Cytherea” is spoken of as shining in the east on the mountain. She is in Pisces, the sign which rises about two hours before Aries, or 4 a.m. at this season, and as the stars are still clearly visible, it is about 5 a.m. The poets have evidently come up from the subterranean passage facing east, for they see Venus first, then Dante turns to his right (south) and sees the four brilliant stars near the south pole, then turning towards the north pole he sees that the Wain has disappeared beneath the horizon, and close beside him he finds Cato, on whose face the Four Stars are shining. Cato tells them that the sun, which is about to rise, will be their guide to reach the Mountain, and as they first go down to the shore, following his instructions, daylight begins to appear.