the first calendar
The first calendar was the moon. A waxing moon eats the dark sky, a waning moon is eaten back. Without the moon, how would we keep dates of months? Without months, how would we know years? Even the most ancient civilisational calendars followed the moon and stars in one way or the other. Days are marked by the sun, months and years by the moon. Because, although the temperature drops, and the days become longer or shorter as the year passes (except near the equator), there is no major change in the structure or size of the sun to suggest a beginning or end, unlike the 'new' moon, or 'full' moon, or 'crescent.'
The beauty of the lunar calendar is that it is not static vis-a-vis the solar calendar. It keeps changing. What would we be without the sun, moon, and stars!