How The Astrology Chart Works
by Jon Stevens

Note: If you are new to astrology, it would be a good idea to first read the article What Is Astrology? as pre-requisite reading.

The chart used in Western astrology is a remarkable system for forecasting events and gaining insight into people, places and things. Although the system in use today was developed across many cultures over several millennia, it achieved a level of refinement with Greek astronomers around 200 A.D. The basic chart system has been modified and improved upon since, and it now exists with some variations.

The easiest way to understand the astrology chart wheel is to think of it as a picture of the solar system. The chart, in fact, is an accurate representation of the positions of the moon and planets as viewed from earth. A chart can be drawn for any moment in time—past, present or future—which allows for observations of the past and present, as well as predictions of future events.

A natal or birth chart, drawn for the moment of birth, is the chart a person uses all his or her life. Throughout an entire lifetime, it will never change . However, the influences acting upon the chart are continuously changing, and these influences bring change to a person's life.

The positions of the sun, moon, earth and planets at the time of birth can reveal many things about a person's personality, character traits and interests. There are several theories as to why this is true. Some astrologers argue that the planetary influences themselves imbue the newborn with the qualities of that precise moment, much like a glassblower who produces a wine glass which forever resonates to a C# on the musical scale. Others suggest that a spirit waiting to be born can only enter into the world when the planetary influences coincide perfectly with the qualities of that spirit. These two very different perspectives present us with an argument that may never be resolved. Most astrologers agree, however, that the true moment of birth is when the baby takes its first breath.

Fig. 1 below shows a basic chart wheel. The twelve subdivisions of the circle, or 'wedges of the pie,' represent the signs of the zodiac. Originally, it was Greek astrologers who brought validity to the idea that the heavens should be divided into twelve equal sections or zodiac signs. The entire zodiac represents the totality of life, while each sign represents a major department of life. Aries, for instance, represents aggression, originality, integrity and identity. Libra represents marriage, partnership, sales/transactions and outward appearance, and so on. The entire circle is divided into 360 degrees; each sign occupies 30 degrees; each degree is comprised of 60 minutes (minutes here is a unit of measurement, not of time).

As can be seen from the diagram, the sun, moon and each of the planets occupies a sign, degree and minute. The order of standard notation is: planet first, then degree, then sign, then minute. So, in the above example, Jupiter () is at 12 degrees, 6 minutes of the sign Pisces ().

Thus far, we have examined a basic wheel of the zodiac. An actual natal chart however, gets a little more complicated. Fig. 2 below is a natal chart which shows some things not normally included in standard notation but which I have inserted for purposes of illustration. The position of the earth in the center of all natal charts, for example, is always implied, or taken for granted. The view of the earth in Fig. 2 is from a vantage point high above the north pole, so that the earth is seen in its normal rotation, i.e., counter clockwise. The figure of the person represents the person for whom the chart is drawn, standing at the exact place of birth. In all natal charts, the longitude of the person's bithplace is always placed directly at the top of the chart. Because the person's birthplace must be at top, the earth is viewed as stationary; thus making the whole zodiac appear to revolve around it. The point in space directly above the person at birth is called the Midheaven. The point at the eastern horizon is called the Ascendant or Rising sign, so called because it is from the eastern horizon that the zodiac signs and planets ascend. In the example below, the Rising sign is Cancer ():

In addition to the zodiac sign system mentioned earlier, there is also a system of twelve houses, named first through twelfth. In fig. 2 above, the wedges of the pie represent the houses, while the multi-colored ring (usually not shown in chart notation) represent the signs of the zodiac. Each black or blue line designates the beginning or end of a house and is called a house cusp. The degree, sign and minute of the house cusp is notated just outside the main wheel in the white ring. The house system is actually a personalized version of the zodiac which is superimposed over the actual zodiac. This makes for a chart which is uniquely tailored to each person.

The placement of the houses is determined by the time of birth along with the place of birth. It's easy to see from the above diagram that if the earth were to rotate twenty degrees more, the whole zodiac would move clockwise, changing the Ascendant from Cancer () to Leo (). This is why a person's time of birth is so critical in casting natal charts. The earth rotates approximately one degree every four minutes, so an error in birthtime of only fifteen minutes would cause the placement of Midheaven and Ascendant (and consequently all the houses) to be off almost four degrees.

Fig. 3 below shows a natal chart in combination with transits. The inner ring of planets is the natal chart; the outer ring is the transits. Transits are the positions of the sun, moon and planets charted for any point in time after birth. Transits are used to forecast a person's future events, to examine the present or to review any event in the past. In a combination chart such as this, the house cusps of the natal chart always predominate. As a result, the natal house cusps are notated outside both wheels. The beginnings of each zodic sign are usually not included in chart notation. By referring to the degree and minute of each sign on the house cusps, the user can easily approximate where the zodiac signs begin and end.

The natal chart never changes, while transiting planets are in constant motion. Events are predicted through the relationship of transiting planets to natal planets. Whenever a transiting planet lines up with a natal planet, a significant event may occur in a person's life. These lineups are called aspects, and they form the basis of astrological interpretation. Since there are different ways that planets may line up with each other, there are different types of aspects. The most commonly used aspects are:

Simply put, an aspect is the difference in degrees between one planet and another. Remembering that all planets move in a counter clockwise direction, refer to Fig. 3 to locate the aspects between transiting and natal planets. The planets and aspects involved help to determine what type of an event it will be. For instance, notice transiting Jupiter () at the top of the chart. This planet is about to make a conjunction to the natal midheaven. Since Jupiter is associated with travel, education, beliefs and good fortune, and the midheaven is associated with career, we might infer that this person will find some official recognition with regard to career, with the possibility of getting a raise or promotion. Another possibility is very productive travel for business purposes. At the same time, this same transiting Jupiter will form a square to natal sun () at 21° Gemini (). This means that while there will be great advances in career, this native may find himself in a position of being limited creatively, or that the extra demands of career will find him bowing to the needs of the system or the policies of his company.

Another aspect to consider in the above chart is transiting Saturn () at 25° Aries () in opposition to natal moon () at 27° Libra (). Since Saturn is the career planet and the moon represents home, the native may find himself torn between the demands of business and the needs of his family. Also, he may experience difficulty in getting support from his usual business associates and will have to seek help from outside sources. A stressful situation is imposed, but meeting the demands of this opposition can lead to great success.

By examining all of the aspects in this way, noting the exact date each aspect will occur, an accurate forecast of this person's future may be given. In addition, recommendations may be given for dealing with upcoming influences—how to avoid the pitfalls of stressful situations and how to make the most of positive ones.