In the mid-to-late 1800s, many prominent astronomers were pretty sure there was another planet inside the orbit of Mercury, because Mercury's orbit has a peculiar irregularity. They called this yet-to-be-properly-seen planet 'Vulcan', and it became a fixture in astrologers' horoscopes.
In the early 20th century, Einstein came along with his Theory of General Relativity, and with these equations he demonstrated that the sun's gravity was bending spacetime in a way that perfectly accounted for Mercury's wobble. Vulcan was therefore found to be a myth, nonexistent.[1]
Nevertheless, many astrologers still feature Vulcan in their horoscopes even today, over a century later.[2] The inclusion of an entirely fictional heavenly body seems to undermine any other conclusions drawn from planetary positions.
1: https://en.wikipedia.org/wiki/Vulcan_(hypothetical_planet)