The “mystery” that is central to the book is how the Dogon allegedly acquired knowledge of Sirius B, the white dwarf companion star of Sirius A, invisible to the naked eye. Temple did not argue that the only way that the Dogon could have obtained what he understood to be accurate information on Sirius B was by contact with an advanced civilization; he considered alternative possibilities, such as a very ancient, advanced, and lost civilization that was behind the sudden appearance of advanced civilization in both Egypt and Sumeria. He personally found the theory of alien contact more convincing, but he did not claim certainty about it. Noah Brosch explained in his book Sirius Matters that cultural transfer could have taken place between 19th century French astronomers and Dogon tribe members during the observations of the solar eclipse on 16 April 1893. The expedition, led by Henri Deslandres, stayed in the field for five weeks and it is reasonable that during this time many contacts with the locals took place, and that relatively modern astronomical knowledge was then transferred.