In astrology, the larger life of our solar system as a whole tells us something about our own personal Earth life. The interplay and relationship of the planets with one another as they circle the Sun is carefully studied.
Of particular interest to astrologers are the Sun, the Moon, and the planets Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. These are the celestial bodies used most often by modern astrologers for natal interpretation.
Each of these planets represents or refers to a part of our life and self.

At the time of our birth, the planets (through their configurations and relationships) tell us something about how things were when we were born. Each planet points to special qualities within us.
Yet, of all the planets, the two most important planets to astrologers are the "lights," the Sun and the Moon. From where we stand here on Earth, the great shining Sun by day and the reflecting Moon at night are our constant companions. They have much to tell us as to where we have been and where we are headed.

The Sun and Moon (or lights, as they are called) are the two most important bodies. It is sometimes easier to understand what they represent in astrology if we consider how they interrelate with the Earth.

A good analogy is the following. Each of us is on Earth. The bright and shining Sun represents someone older, someone we look up to -- whether that be a teacher or guru. The Moon represents someone younger, especially the groups that we used to belong to. That is the analogy. Here is how we might think about it:
We can't live either on the Sun or Moon. We have grown out of and beyond the younger generation (Moon). Out of it we once came or were born. This is why the Moon is said to be a mystery. It is both our parent and our child.
Regardless, we no longer are alive to what moves the younger generation. The same kind of reasoning is true of those older than us, who have taken more degrees of experience. We are still too young... not yet ready to live in the solar environment. We receive light from the Sun, and it makes life grow.

We each have both a Sun and a Moon. In the course of a month, these two bodies take up various positions in relation to where we are on Earth. At the Full Moon, the Moon is beyond the orbit of the Earth (farther out) and reflecting sunlight back on us.
At the New Moon, the Moon is within the Earth's orbit and lost in the Sun.
Tradition suggests that we start (or may receive) an impulse at the New Moon, build and develop it for two weeks until the Full Moon, and then gradually understand or draw some conclusions from the experience during the two weeks after the moon is full.