The sudden disappearance from the sky of familiar luminous bodies causes the gravest apprehension and dread among primitive peoples as it did among the most ancient ancestors of humanity. Typically it is the total eclipse of the sun that is most frightening, but in the partial eclipses of the sun and moon also, a giant dark shadow is seen moving over the celestial body as though it were devouring it. This shadow is given the reality in diverse cultures of being a great monster, or beast. The fear that the sun might not return after such an eclipse caused rites of propitiation. The dread of eclipses may be one of the fundamental fears that primitive religion was organized to counter.
When the apparent diameter of a covered body is much smaller than that which hides it, it is said to be occulted. Occultations involve stars, nebulas or distant planets which may be hidden by the moon or nearer planets or, to take a particular example, the occultation of the Crab Nebula by the Solar corona (as measured by radio astronomy). Therefore early man may have been frightened by occultations as well as eclipses. Besides the sun or moon, notable stars may have vanished for such reasons. However, since there is a periodicity to these events, records would have assured the ancient peoples that they were only passing evils if not merely natural phenomena; so there appears to have been an occultation that was not periodic, but was catastrophic, to which all subsequent fear referred back.