Caltech researchers have done the math and it shows a rogue ninth planet orbits the sun every 15,000 years. Is there any evidence in recorded or oral history that might be able to identify this occurrence?
The theorized ninth planet would orbit the sun at a mean distance of 600 AU (that is 600x the distance of the Earth to the Sun). Uranus, for comparison, is mere 18-20 AU away is only barely visible on extremely rare occasions. Neptune, at 29-30 AU away, is never visible. So this hypothetical Planet Nine is ~20x further away than Neptune and would never be visible to the naked eye at any point in history.