20. Loony

The moon shifts rapidly across a background field of stars, about ½ degree an hour. Hence errors in calculation of the moon's position come to light expeditiously, and they are readily noticeable to astronomers observing the sky and to historians checking ancient records.

The moon's advantageous features are counterbalanced by the complexity of its orbit. Astronomers since Babylonian times have struggled to discover and describe the cyclical patterns traced by the moon. Thousands of observations of the moon in cuneiform texts attest to the close attention paid to lunar comings and goings.