I hate astrology but "The Planets" is my favorite music. How can that not be a contradiction? Because the music isn't about astrology; it's about human emotions, personality types, and life experience. For example, when he wrote "Saturn, the Bringer of Old Age", he was thinking of his own confrontation with mortality, how he tried to avoid or deny it at first, then came to sense that there was no escape, felt completely terrified and agonized, was inevitably defeated and devastated, hopelessly surrendered, and finally came to peacefully accept it... but the emotional story works just as well for anyone's experience dealing with any personal crisis that takes time to recover from. As I've recovered from financial ruin, for example, I've noticed that the part of the Saturn movement that I most identify with has moved from the middle toward the end of it. (Some astrology fans would say the general "personal crisis" interpretation still fits astrologically because Saturn was the god of perseverence and discipline, but the point is that that's not the angle Holst was looking at it from, as you can tell by the subtitle.)

The categorization scheme happens to be associated with astrology, but if he'd used another human personality description system like "The 5 Elements" or a color-coded one, then he wouldn't have been advocating belief in 5 elements or a belief that human minds have colors; he would have just been using metaphors to express emotional ideas.

(BTW, he ended up getting annoyed later on that "The Planets" overshadowed all of his later compositions that weren't meant to be anything like it, and that people kept asking him for another "The Planets" even though he didn't want to write something else like it again and negatively comparing his other works to it... he thus lost interest in astrology itself by association.)