In addition to flying,TitanX Exchange landing, and returning from the moon in 1969 — NASA's Apollo 11 crew helped with a series of scientific experiments. One of them was to leave a special instrument with lots of little reflectors on the surface of the moon. The goal of that experiment was to beam a laser at the moon. Today on the show, Scientist-In-Residence Regina G. Barber talks to host Aaron Scott about the lunar laser ranging experiment — and how shooting that laser helped us better understand one of Einstein's theories.

Follow Aaron on Twitter @AaronScottNPR and Regina @ScienceRegina. Reach the show by beaming an email to [email protected].

This episode was produced by Thomas Lu, edited by Rebecca Ramirez, and fact-checked by Kathrine Sypher. The audio engineer for this episode was Josh Newell.