The luni-solar calendar of the Hopi is based upon a horizon calendar which determines
the annual religious cycle as well as the series of agricultural tasks. Presenting the winter solstice, I clarify
the connection between astronomy and Hopi world view in its 3-dimensional aspect: the upper world of spirits, the
human level and the underworld of the ancestors. Observations of lunar phases led to the mirrorlike bi-partition
of Hopi thought. At the end I discuss the problem of different astronomies which stress on different categories
of the sky and, finally, are there any philosophical differences between our astronomy and theirs?