"What's that?"
"Which way do we go when we hit the line? The D.D.'s are spaced ninety degrees apart. We might be within a hundred miles of one. If we head the wrong way, we'd have three or four hundred miles to go. There's no method of figuring our longitude."
Morley was staring sunward, with thoughtful eyes. "Yes, there is," he said quietly.
Madsen's jaw dropped. "Give," he said.
"We both forgot something we know perfectly well. Notice the sun? It hasn't moved perceptibly since we landed. Japetus doesn't revolve on its axis."
"So what?"
"Two things. One, no night, since we're on the sunward side. The sun will move from side to side in the sky, reaching its lateral limits when Japetus is in quadrature in regard to Saturn. If we were here for a month, we'd see Saturn rise, make a full arc through the sky, and set. Let's hope for a shorter stay."
"Go on," said Madsen, and suddenly there was nothing patronizing or scornful in his voice.
"Two. We came in over the Pole almost exactly at inferior conjunction. Right?"
"I think I get it." Madsen answered slowly.