Even Homer nods
I love Bernard Cornwell's historical novels. He's one of the best.
However, I just finished reading The Archer's Tale,
about an Englishman at the Battle of Crecy. The King of France is pushed into hurrying the battle by bad advice given by his nobles, backed up by an astrologer. When someone asks what the horoscope for the next day will be, the astrologer replies, "Neptune approaches the bendings tomorrow, sire. It is not a hopeful conjunction."
I have no clue what "bendings" might be. This may all just be astrological hokum. But I do know that the planet Neptune was not discovered and named till five hundred years after the Battle of Crecy.