A lunation is the term for the Moon passing through all of its phases, which takes 29 ½ days and was obviously the basis for the calendar month. A lunation always begins with the New Moon, which happened last Sunday, September 25. Every evening thereafter the Moon sets nearly an hour later while growing from a skinny crescent low in twilight and meanwhile waxing fatter and ascending higher. The Moon is officially “two days old,” then “three days old” and so on as astronomers count the nights since the New Moon.
A week after the invisible new Moon phase, the ever-fattening crescents finish their job by creating the First Quarter Moon, which is an obvious half Moon that conveniently stands at its very highest point at nightfall. This is the best time to see stunning detail through any telescope. I now have a second observatory near my home in Willow, housing a telescope widely regarded as the world’s best for the Moon and planets, and which uses a laboratory-grown mineral (fluorite) for its main lens rather than glass. This set-up, costing as much as a good midsize car, delivers astonishing both eyes-open 3-D views, inspiring me to devote three years to memorizing the Moon’s fascinating detail. People who took my advanced observers’ classes decades ago are welcome to now contact me at (845) 679-0785 and reserve a spot to informally explore the Moon. Any month can work except January-March because of excessive ice on the motorized dome.
This offer is valid for former students and Moon fanatics during the five-day optimum observing window each month that stretches from two days before First Quarter to three nights after that phase. Moon phases are published in most calendars and newspapers. No fee — it’s my pleasure to share the amazement. As to why the first quarter looks best, lay a flashlight flush against a wall with the room’s lights turned off, and the sideways torchlight will make the wall show every dimple and bump and every joint-taping imperfection. Then shine the light straight down on the surface and all detail vanishes — the wall now looks perfectly flat. Same with the Moon. The Full Moon is when the Sun shines straight down making craters and mountains disappear. It’s the worst time to observe the Moon.
Back to our lunation chronology. The Moon keeps fattening or waxing after the first quarter, spending a week in its gibbous state, the phase least well known by the public. Gibbous is simply every shape – slightly resembling a football – that’s fatter than half but thinner than full. During this time period many of its best features materialize, such as Copernicus, a young stunning crater whose inner walls are terraced like Asian rice fields. And Clavius, whose floor houses a strangely curved arc of craterlets, each smaller than the previous one. And the very best mountain range, the Apennines, just above the Moon’s midpoint. And a 300-mile-long cliff as high as the Empire State building — the Altai Scarp. And the gorgeous Bay of Rainbows, Sinus Iridum, guarded by two promontories like the lions flanking the stairs to New York’s main library.
A week after the detail-packed Half Moon we get the telescopically useless Full Moon, even if its aqua radiance on our rural countryside is nothing short of fairylike. Plus it’s the only phase that can be eclipsed! It does this by going into Earth’s shadow, which will actually happen at the next Full Moon on November 8.
After Full Moon, our lunar neighbor rises later and later to strictly become a wee-hours object visible at times like 3 a.m. or before dawn.
Observers change their focus during that fortnight, as the dark moonless heavens bring the gift of deep-space wonders and such until the next lunation arrives with the ensuing New Moon, coming up on November 23 and then December 23.
With some cultures still marking time and creating calendars and holidays according to lunations, a look at its meaning was probably long overdue on this page.