That evening, after dinner, Professor Ditson took Jud and the boys out for a walk along the beach which stretched away in front of them in a long white curve under the light of the full moon. The night was full of strange sounds, and in the sky overhead burned new stars and unknown constellations, undimmed even by the moonlight, which showed like snow against the shadows of the jungle. Professor Ditson pointed out to the boys Agena and Bungula, a noble pair of first-magnitude stars never seen in the North, which flamed in the violet-black sky. As they looked, Will remembered the night up near Wizard Pond before the bear came, when Joe had told him Indian stories of the stars. To-night, almost overhead, shone the most famous of all tropical constellations, the Southern Cross.
Professor Ditson told them that it had been visible on the horizon of Jerusalem about the date of the Crucifixion. From that day, the precession of the equinoxes had carried it slowly southward, and it became unknown to Europeans until Amerigo Vespucci on his first voyage saw and exultantly wrote that he had seen the "Four Stars," of which the tradition had lingered. The professor told them that it was the sky-clock of the tropics and that sailors, shepherds, and other night-wanderers could tell the time within fifteen minutes of watch-time by the position of the two upper stars of this constellation.
"It looks more like a kite than a cross," interjected Jud. "What's that dark patch in the Milky Way?" he inquired, pointing to a strange black, blank space showing in the milky glimmer of the galaxy.
"That must be the Coal-sack," broke in Will, before Professor Ditson could reply.
"I remember reading about it at school," he went on.
"When Magellan sailed around Cape Horn, his sailors saw it and were afraid that they would sail so far south that the sky wouldn't have any stars. What cheered them up," went on Will, "was the sight of old Orion, which stays in the sky in both hemispheres," and he pointed out the starry belt to Jud and Joe, with the sky-king Sirius shining above it instead of below as in the northern hemisphere.
As Jud and the boys stared up at the familiar line of the three stars, with rose-red Betelgeuse on one side and fire-white Rigel on the other, they too felt something of the same comfort that the old-time navigators had known at the sight of this constellation, steadfast even when the Great Bear and the Pole Star itself had faded from the sky. As they continued to gaze upward they caught sight of another star, which shone with a wild, blue gleam which rivaled the green glare of the dog-star, Sirius. Professor Ditson told them that it was Canopus, Mohammed's star, which he thought led him to victory, even as Napoleon believed that the planet Venus, seen by daylight, was his guiding star. Then the professor traced for them that glittering river of stars, Eridanus, and showed them, guarding the southern horizon, gleaming Achernar, the End of the River, a star as bright as is Arcturus or Vega in the northern sky. Then he showed them Fomalhaut, of the Southern Fish, which in the North they had seen in the fall just skipping the horizon, one of the faintest of the first-magnitude stars. Down in the southern hemisphere it had come into its own and gleamed as brightly near this northern horizon as did Achernar by the southern. It was Will who discovered the Magellanic Clouds, like fragments of the Milky Way which had broken up and floated down toward the South Pole. These had been also seen and reported by Magellan on that first voyage ever taken around the world four hundred years ago.