NPR: Back in 55 B.C., Julius Caesar invaded Britain for the first time. He kept a detailed record of his journey, straightforward enough for Latin students to read today. But in that record, Caesar failed to mention the actual date of his landing.

It's a puzzle that's had scientists and historians duking it out for centuries. Now, Donald Olson, a professor of physics at Texas State University, thinks he's got the answer. He explains how the stars aligned to shed light on this ancient mystery.