On the evening of 23 November, the moon will have a close encounter with the star Pollux, the brightest star in the constellation Gemini, the twins. Pollux marks the head of one twin. The other twin is marked by the star Castor. Although Pollux is the brighter star, it was Castor that was given the designation alpha Geminorum by German astronomer Johann Bayer in his 1603 star atlas Uranometria, which was the first to chart the entire celestial globe. Although Bayer mostly designated stars in brightness order, by giving Pollux the beta Geminorum designation we can see that this was not a hard and fast rule. The chart shows the view looking east from London at midnight as 23 becomes 24 November. The moon will be in a waning gibbous phase, with almost 83% of its visible surface illuminated. In Greek and Roman myth, Pollux is the son of Leda and the divine Zeus, who seduced Leda in the guise of a swan, while Castor’s father is the mortal king of Sparta. Leda just happened to carry the two boys at the same time, hence twins. From the southern hemisphere, the view will be similar. From Sydney, Australia, look north-east after midnight.