The Moon in Motion—The Basics
The Moon's movement is tracked in two different ways that take place simultaneously. Both are based on the Moon's unique position as a satellite of Earth: We circle the Sun, and the Moon circles us. In figure 77, the Moon is shown in its Full position, on the far side of the Earth, away from the Sun. We'll meet inner planets Mercury and Venus shortly, but you can see here that neither of them can get far enough from the Sun to be on the far side of Earth.
The first way we can track the Moon is through its sidereal period, which views the Moon in relation to the stars. The Moon moves through the entire zodiac in an average of 27.3 days.
The Moon's phases, however (its shifts from New to Full to New), are created via a different timeline—the Moon's synodic period, which tracks its place in relation to the Sun. This cycle averages 29.53 days.
Phases are our main way of knowing the Moon. As the Moon orbits the Earth, the Sun's light always illuminates just one side of the Moon, leaving the other half in shadow (see figure 78).
Figure 78 shows how it would look viewed from the side. But the view is different and far more interesting from our earthly vantage point, although only our perspective has changed. In figure 79, the cycle begins with the Dark of the Moon, as Sun and Moon are conjunct, with the Moon so directly in line with the Sun that we can't see it at all. In a day or two, it appears as a New Crescent, first visible in the western sky just after sunset. The solid edge of the Moon's curving shape fits into your curved right hand, like a backward letter C. As the days pass, the Moon is higher each night as the Sun sets, leading to a Full Moon rising in the east as the Sun sets in the west, at opposite sides of the sky—that is, as the Sun and Moon are in opposition. The Moon takes two weeks to move from Dark to Full, consistently rising later each day (how much later depends on your location and the season).
Figure 80 takes us through the next two-week period. The Full Moon that rose at sunset in Figure 79 is visible all through the night—beautiful!—and sets as the Sun rises. But on each night that follows the Full Moon, the Moon is slimmer, its right-hand side whittled away as it rises after sunset and lingers until dawn. Now the solid edge of the Moon's shape fits your curved left hand, like a letter C. By rising later each day, it catches up with the Sun, shrinks to a tiny crescent, and then finally isn't seen at all. It's conjunct with the Sun again, Dark, directly in line and not visible to us until it reappears in the west at sunset.
We can see the Dark Moon—sort of—during a solar eclipse. As the Dark Moon moves directly between the Earth and the Sun, we see the Moon in silhouette for a few minutes, and the brighter stars may appear in the darkened sky. This magical event is possible because, from our perspective, the Sun and Moon are nearly equal in size, 1/2º of space each. A smaller or more distant Moon wouldn't cover our Sun.
Lunar eclipses happen during some Full Moons, when the Earth is so directly placed between the Sun and Moon that its shadow falls across the Moon's face, turning it dark gray or a bloody rust-brown—a possible source of the tradition that associates the colors white, red, and black with the archetypes of Maiden, Mother, and Crone, with the red symbolizing a woman's fertile years.
Eclipses reveal that which is otherwise invisible. During a solar eclipse, we see the Moon cross directly between the Earth and the Sun, which gradually gave our ancestors an understanding of the Moon's place and orbit. During a lunar eclipse, they saw the Earth's shadow crossing the Moon and came to understand that the Earth is round.
Solar eclipses are only visible to those in the area where the Moon's shadow falls across the Earth. Lunar eclipses, on the other hand, are widely visible. If you can see the Moon, you'll probably see the eclipse (see figure 81).
To put sidereal and synodic cycles together, picture a Full Moon on the Aries-Pisces border. In 27.3 days, the Moon travels through all the other signs and returns to its Aries-Pisces starting point, but it isn't Full again yet. That takes another 2+ days, when our Full Moon is in line with Taurus. The Moon takes an average of 2.25 days to move through each zodiac constellation, so, as a general rule, each Full Moon will be in the next sign. Full Moons occur when the Moon and Sun are opposite each other in the sky, so the Full Moon's place in the zodiac is always opposite that of the Sun. (Sadly, this can't compensate for those pesky irregular-sized constellations.)
The Moon in Motion—The Fine Details
While the Moon is one of the easiest planets to locate in the sky, its motion is one of the trickiest to understand. It's a good thing our ancestors paid attention and helped mark the way.
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