The Moon is second only to the Sun in terms of the brightness of all the celestial bodies we see here on Earth. Her regular monthly cycle has been imprinted on human consciousness since the dawn of time.
The Moon is a companion to the Earth, circling the Earth even as Earth circles the Sun and completing its entire lunar cycle in 29.5 days. Just like the Earth, half of the Moon is always lit by the Sun, but as the Moon orbits around us, the angles between the Earth, the Moon and the Sun change. We can only see a portion of the moon's surface as it orbits, and this creates the Moon's phases.
The Moon is large and close enough to have a gravitational attraction here on Earth. For example, the Moon pulls on our oceans, resulting in the tidal ebb-and-flow of all large bodies of water. Not surprisingly, the Moon is strongly associated with water, and since humans are mostly water, the Moon is also said to affect humans.
The Moon moves fast, taking only two to three days to move through each Zodiac sign -- all the while cycling through the eight lunar phases each month and repeating on a micro level the cycles of human endeavor.
The first of these phases is called a New Moon, which symbolizes the emergence of new ideas, new projects and thoughts brewing in the unconscious. The Moon then grows for almost two weeks until it reaches the culmination of the cycle at the Full Moon. The Moon then shrinks in size until the whole cycle starts anew.
These phases represent the trials, challenges and rewards of our labor.