It’s not easy to locate, let alone put yourself exactly at, what navigators call a star’s substellar point, the precise spot on Earth that is directly under a star at any given moment. No star visible at night is strong enough to light up even a pinpoint on the ground to confirm that you’re directly under it. So you need a sextant. The wise men in the Bible’s book of Matthew—the ones looking for the baby Jesus—didn’t have a sextant. That navigation tool wouldn’t be invented for centuries. This probably explains why, though they were following a star, they also stopped to ask Herod, the king of Judea, for directions (see 2:1–12).

Herod’s advisors knew only the prophecy that one who would rule Israel would come out of Bethlehem. But the wise men’s question, “Where is he that is born King of the Jews?” convinced Herod that this child was a threat to his crown, and he plotted to kill him. He asked the wise men to tell him when they found the child, pretending that he wanted to pay homage. The wise men did find Jesus and offer their gifts. Then they left without returning to Herod, having been warned by God of the king’s plans.

But why did Herod need directions from them? After he spoke with them, the star seems to have begun to shine with such intensity that, unlike any other star in the night sky, it lit up its substellar point, the stable where Mary had given birth to Jesus. The wise men just followed the star. So why then couldn’t Herod’s assassins simply follow that light just as the wise men had?