Few readers will have the competence and perseverance to master the materials Temple sets forth in suggesting his answer to the question that is the subtitle. He begins jocosely, a hint of Holmes' Dr. Watson in his voice, but soon moves into sacred traditions where the mind not only bends but warps into knots. The helpful summaries at the end of the chapters help less than he may have hoped. The problem he tries to dent is intriguing. How did the religion of a little known African culture (the Dogon of the Sudan) incorporate information about the star system Sirius which our astronomers have but recently learned? The mystery centers on an invisible ""white dwarf' star that orbits Sirius. The Dogon not only knew this unseen body was there but made it a focal point of their greatest rites. Temple works out a theory relating the ancient gods and myths of Sumeria, Egypt, and Greece which also center on Sirius and its two star-planets. Sirius, also known as the Dog Star, is the brightest star in the heavens, and represented in Sumerian and Egyptian inscriptions as a dog or jackal. In Dogon cosmology the ""white dwarf"" star is all important: ""Its movement on its own axis and around Sirius upholds all creation in space. . . its orbit determines the calendar."" Temple believes, more or less, that Earth was once visited by beings with a ""magical technology"" who encoded certain knowledge and wisdom into the mystery religions of the East, knowledge that Western science only now is beginning to unlock.