The Dogon astronomical knowledge of Sirius B was documented by anthropologists Marcel Griaule and Germaine Dieterlen in the 1930s–1950s, but subsequent researchers have questioned whether the detailed star knowledge was present before Western contact or introduced by visiting astronomers. Sirius was widely studied by Western astronomers from the 1840s onward, and the Dogon had contact with European missionaries. The 'Nommo' are water spirits in Dogon religion, not literal aliens.