The Birth Chart
When someone asks, “What's your sign?” she's really asking “Where was the sun positioned in the sky on the day you were born?” Astrology divides the sky into twelve sectors and links them with the signs of the zodiac. From Earth, the sun appears to travel through all twelve sectors during the course of a year, spending about thirty days in each sign. This is the simplest (and most simplistic) form of astrology, usually called sun sign astrology. It has some validity, but at the same time this method is too general to offer much insight.
Like most of the arts and sciences, astrology contains many different branches and many schools of thought. The one most people are familiar with is called natal astrology. A natal or birth chart is based on the date, time, and place of your birth. An astrologer calculates the positions of the sun, moon, planets, and other significant heavenly bodies to produce a blueprint of your innate talents, life challenges, potentials, traits, and characteristics. The birth chart thus provides a detailed and amazingly precise picture of you.
Because human beings are mainly concerned about what's happening on Earth, most astrological charts are based on a geocentric perspective, that is, from the vantage point of Earth. From this perspective, the sun appears to travel across the sky, though of course that's not really the case. Heliocentric astrology considers the positions of the planets and their cycles as if they were begin viewed from the sun.
The sun isn't the only heavenly body that has a sign associated with it. The moon, planets, and asteroids — everything in the sky, in fact — were also positioned in zodiac signs at the moment of your birth. You not only have a sun sign, you also have a moon sign, a Mercury sign, a Venus sign, and so on. Each body possesses its own inherent energy, nature, and mode of expression, and each governs a particular area of your life. Venus, for instance, rules relationships. The zodiac signs color the energies of these bodies and influence their expression. Therefore, a person with Venus in Taurus will experience relationships differently than someone with Venus in Sagittarius.
A birth chart resembles a wheel with twelve spokes or a pie cut into twelve pieces. Each of these pieces is called a house. (These divisions are determined by mathematical calculations too involved to cover here, but you can find many good books devoted to the subject.) The houses represent the areas in your life: money and material resources, partnerships, home and family, and so on. The heavenly bodies fall into one or another of these houses. Astrologers look to see which bodies occupy which houses in order to understand how things are likely to play out for you in the various parts of your life.
The relationships between the sun, moon, and planets are significant, too. Depending on their positions at the time of your birth, some celestial bodies will likely form special connections, known as aspects, with each other. When two or more bodies are linked by an aspect, they influence each other. Some connections are harmonious and supportive, but others cause stress and challenges.
“Astrology [shows us] that there is a rhythm to the universe and that man's own life partakes of this rhythm.” — Henry Miller
Of course, there's a great deal more to natal astrology than this chapter has touched on, but these are a few of the basic details to remember. The birth chart is the starting point for predictive astrology. From here, an astrologer can look at the positions of the heavenly bodies at any given time in the future or calculate other types of charts and give you a good idea of what lies ahead.