The yellow sun dropped completely behind the north slope of the V notch and he went on to the caves. He found Craig and Anders, the only two who might know anything about Ragnarok’s axial tilts, and told them what he had seen.

“I made the calendar from the data John gave me,” Anders said. “The Dunbar men made observations and computed the length of Ragnarok’s year⁠—I don’t think they would have made any mistakes.”

“If they didn’t,” Lake said, “we’re in for something.”

Craig was watching him, closely, thoughtfully. “Like the Ice Ages of Earth?” he asked.

Lake nodded and Anders said, “I don’t understand.”

“Each year the north pole tilts toward the sun to give us summer and away from it to give us winter,” Lake said. “Which, of course, you know. But there can be still another kind of axial tilt. On Earth it occurs at intervals of thousands of years. The tilting that produces the summers and winters goes on as usual but as the centuries go by the summer tilt toward the sun grows less, the winter tilt away from it greater. The north pole leans farther and farther from the sun and ice sheets come down out of the north⁠—an Ice Age. Then the north pole’s progression away from the sun stops and the ice sheets recede as it tilts back toward the sun.”

“I see,” Anders said. “And if the same thing is happening here, we’re going away from an ice age but at a rate thousands of times faster than on Earth.”

“I don’t know whether it’s Ragnarok’s tilt, alone, or if the orbits of the suns around each other add effects of their own over a period of years,” Lake said. “The Dunbar Expedition wasn’t here long enough to check up on anything like that.”