No matter which system you go by, the names of the two brightest stars of Gemini aren’t quite right.

In mythology, the stars are named Pollux and Castor. They represent a pair of twin half-brothers. They had the same mother, but one had a mortal father, while the other was the son of Zeus, the king of the gods of Olympus. But the stars don’t look like twins. Pollux is almost twice as bright as Castor, and it looks orange, versus Castor’s pure white. They were called the twins mainly because they’re both bright, and they appear close together.

The stars themselves aren’t physically related. And they’re nothing alike. Pollux consists of a single giant star, while Castor is a system of six stars.

A second naming system is also off. In this system, Castor is Alpha Geminorum, while Pollux is Beta Geminorum.

The naming system was devised by Johann Bayer. In a star atlas published in 1603, he assigned each star to a constellation. And he named the stars using the letters of the Greek alphabet. “Alpha” usually was applied to a constellation’s brightest light, and “Beta” to the second-brightest. But in Gemini, they’re reversed. No one is quite sure why that’s the case. No matter the reason, though, the names of the bright “twins” of Gemini are a bit off.

The stars appear near the Moon early tomorrow. Pollux stands above the Moon at first light, with Castor a little farther to the upper left of the Moon.

Script by Damond Benningfield