The Dogon and Sirius B
The account
The Dogon people supposedly knew that Sirius has a companion star invisible to the naked eye, knowledge given to them by amphibious beings who came from there.
What investigators found
The accounts come from the French anthropologists Marcel Griaule and Germaine Dieterlen. Later research by Walter van Beek found no such knowledge among the Dogon, and outside influence is suspected.
The story
The Dogon live on the cliffs of Bandiagara, in Mali, in West Africa. In the 1930s and 1940s, the French anthropologists Marcel Griaule and Germaine Dieterlen lived among them and published that their priests knew of a companion star to Sirius, small, extremely heavy and invisible to the naked eye.
That star exists: it is Sirius B, a white dwarf first photographed in 1970. In 1976, the writer Robert Temple published "The Sirius Mystery," arguing that the Dogon had received this knowledge from amphibious beings who came from that star system.
Years later, the Dutch anthropologist Walter van Beek spent years living with the Dogon and found no one who knew of the star. One explanation is that the knowledge arrived through contact with Europeans, since Sirius B had been in the news since the 19th century, or that it came from the researchers' own interpretation.