Every March 14, University of Missouri Professor Stephen Montgomery-Smith’s wife buys him a pie — a lighthearted nod to his career and to π, the never-ending, never-repeating number that begins with 3.141592 and goes on forever.

More precisely, pi is a circle’s circumference divided by its diameter, a simple calculation quietly embedded throughout the world around us.

“Pi is like the oil or butter in the pie crust,” Montgomery-Smith said. “It’s essential but just there. Most people don’t think about it.”

Montgomery-Smith, however, is not most people.

By the age of 11, he was reading about the science of optics and lenses. At 13, he began teaching himself calculus. And over the course of his career at Mizzou’s College of Arts and Science, he has built a reputation for bridging deeply abstract mathematical concepts and real-world applications. It’s a balance that now underpins work he’s doing for NASA, where he helps develop simulation systems for lunar terrain vehicles, using π to calculate rotations, curvature and motion.

“For me, every day is Pi Day,” he said.