It’s the crescent moon I’ve been thinking about and watching lately. I’m always filled with a familiar sense of wonder, month after month, year after year, when I watch the crescent moon in the pre-dawn sky as it moves from last quarter to new. Each morning the crescent arc is thinner, and the moon has moved about a half a constellation east, closer to the horizon where the sun will soon rise. Last night was last quarter. Tomorrow I’ll see the crescent arc.

The thing that so persistently fascinates me about the crescent moon, when it’s near new is the transition from waning crescent to new, and then to waxing crescent, over three or four days at the end / beginning of the lunar cycle. Positionally the moon had moved 30° or 40° along the arc of its orbit around earth. In those three days it’s visibility had changed from morning twilight to evening twilight…. because it was now on the other side of the sun.

It’s this physical and emotional affirmation of an abstract science concept, known and understood since grade school in it’s most rudimentary form, that thrills me. The moon waxes. The moon wanes. You can really understand it in your bones when you observe this magical transformation: how the earth turns, how the sun rises and tracks across the sky, and how the moon passes from west to east of the sun. “They’re all in the same plane. They’re all going around in the same direction… It’s perfect, you know. It’s gorgeous. It’s almost uncanny” to quote astronomer Geoffrey Marcy. Our beautiful dance to the music of the spheres.

A fascination with the moon in its daily transition often leads my thoughts to the calendar. The lunar cycle has been the organizing principle of many calendars. But it’s always been at odds with the unit of time we call a ‘day’ – local noon to local noon, our intrinsic unit of division, when the sun touches the zenith – and the tropical or solar year, the time it takes the earth to make one complete orbit of the sun. These cycles don’t just don’t mesh. None of the units are divisible by whole numbers. A lunar month is 29.5306 days. A solar year is 265.243 days. There are 12.368 lunar months in a solar year. A lot of early calendars – those of the Babylonians, the Greeks, the early Romans – were lunar at the core, with corrections that would align the lunar cycle with the solar year, in order to keep the seasons positioned correctly.

The Egyptians had a purely solar calendar. 12 months of 30 days, plus 5 days at the end (or was it the beginning?) of the year. Three weeks of 10 days each month. This calendar used the first sighting of Sirius in the pre-dawn sky to mark the beginning of the year. This named the time to prepare for the floods, when the Nile would bring its rich loam to the plains. Each ten days a new group of stars, one of a group of 36 Decan stars, would be sighted and noted, and so the year progressed in Egypt. Three seasons: flood, sow, and reap.

I think about that person, that Egyptian astronomer priest straining at first light for the first glimpse of Sirius, the weight of that moment. I wonder about their eyesight. I wonder if that person had a sharp eyed child to help. Or was it a group of priests, working together? Did they drink coffee? When did coffee get invented? Did they know the trick of looking near the anticipated location the star… because our peripheral (averted) vision is better at picking up those dim objects than our direct vision?

Back to the early Romans… the Calends, from the Latin Kalendae, meaning “the called,” corresponds to the first day(s) of each month of the lunar calendar. This is the derivation of our word ‘calendar.’ Like the Egyptian who called out the heliacal rising of Sirius, the Romans had a astronomer priest who ‘called out’ the first sighting of the crescent moon in evening twilight, and thus marked the beginning of a new month. I’ll be watching, and report back to you.