Another Pretty Good Puzzle

I made this one up awhile ago when a full October moon loomed huge over the Easy Bay hills ---

The year was AD 2129, and the China-Halliburton planetary exploitation conglomerate was just getting started with its lunar titanium mining operations. Neil and "Buzz", two "Geo-Scouts" for the company, had just stepped out of the cafeteria dome after lunch and stood in the open in their spacesuits, looking up at the Earth, a wide crescent of brilliant white streaked turquoise suspended against the hard black of space directly overhead.

"You can just make out my home city," Buzz said, "right there at the edge of the penumbra above the Antarctic. Wanaka. See the lights just coming on?"

"Never been there," Neil said.

"Pretty city," Buzz mused. "Small, too, only about 16, 17 million. Say," he suddenly lit up, "wanna race?"

"Sure!" Neil exclaimed.

As Geo-Scouts Neil and Buzz used "bent-grav scooters" to scout the lunar surface for craters bearing the signature marks of titanium rich meteorites that had buried themselves in the lunar surface aeons ago. The bent-grav scooters employed a drive made possible by a recent discovery that gravity's force could be locally redirected, or bent, using a specially twisted coil of electromagnet in combination with a few paperclips and a large rubber band (the discovery had been accidental). A scooter with the drive active would hover just above the surface and accelerate horizontally with a force just a little less than the local gravitational attraction. On the Moon, with no atmosphere to cause drag, the scooters could reach speeds as high as 500 MPH in minutes, and coupled with computer driven auto-terrain following autopilots, racing the scooters was a thrill like no other.

Within minutes Neil and Buzz were hurtling across the lunar terrain at top speed, and for well over an hour they dipped and weaved over and around the Moon's tortured terrain, each trying to shake the other. Finally they decelerated to a stop, exhausted.

"You're gonna have to lead us back to base," Neil said, "My nav-chip seems to have fried itself."

Buzz turned white inside his helmet. "Then we're toast. I'd pulled my nav-chip for reprogramming. I was following you."

It was Neil's turn to go white. "I don't have any idea where we are. s**t. We must be at least 400 miles from base, could be 600. We don't have the oxygen to do anything but go straight back, but which way?"

"We're beyond radio coverage, too," Buzz moaned. "Crap!"

"I should've paid attention back in astronomy class. I don't know one star from another."

"That makes two of us."

Neil looked up at the Earth, by now no longer overhead, overcome with a strong longing to be home. The shimmering crescent looked close enough to touch. "Buzz!" Neil suddenly exclaimed, "We aren't lost! Follow me!" And Neil started his scooter at full acceleration. Buzz, startled, banged down hard on the go lever and followed.

"You sure you know where you're headed?" Buzz asked as the lunar surface became a 500MPH blur beneath their scooters.

"Positively," Neil answered, and gave a three word explanation.

"Goddamn!" Buzz said. "I'm glad one of us has a brain!"


What was Neil's explanation that led the pair unerringly back to base?