Strictly speaking in order of time, the first class of uniformities from which the measurement of time proceeded were in all probability the lunar phenomena, from which we got the grouping of days into months and weeks (quarter months).
There are still backward peoples who have not learned to reckon in years of equivalent length. The recognition of the month is wellnigh universal even among hunting tribes with no settled agriculture. Moonlight is a circumstance of enormous importance in the everyday life of people who have crude means of artificial illumination. Even today in remote parts of the country the time of full moon is chosen for a long night journey.
The moon seems to partake of the general motion of the celestial sphere, rising in the east and setting in the west. If it rises at the same time as a particular star cluster on a particular night in the month, the same constellation will rise a little earlier than the moon on the night following. A week later it would already be above the pole at moonrise. Thus the moon itself seems to be slipping backwards in the opposite direction to the apparent rotation of the sun and fixed stars, so that it gets back to where it was before after a definite interval of days and nights, i.e. what we call roughly a month. Alternatively we may say that it rotates round the earth in about a month in the same direction as the earth's axial or diurnal motion. Whichever way we look at it, the moon has a motion of its own, independent of the apparent motion of the fixed stars.