Understanding The Birth Chart

When seeing an astrology birth chart for the first time, it looks like a complicated and hard to read structure.

Structure Explanation

astrology birth chart zodiac sign rising angle
The birth chart is initially a circle divided in 12 equals parts of 30°. One for each house. It starts on the left (i.e. 9 AM) and goes round anti-clockwise. This type of division is an equal house chart, because each house has the same size (30°). There are also unequal house charts, such as the Placidus or Koch house systems, where house sizes are unequal.

Then, astral items are positioned according to their rising angle in the sky at the birth date. If, for example, Jupiter has a rising angle of 74°, it would be located in Gemini, which starts at 60° and ends at 90°. In this case, one says Jupiter is at 14° in Gemini (74°-60°=14°). This is the information found in ephemeris tables.

Natural And Solar Charts

The resulting chart still has to be rotated before becoming the final birth chart. Two cases are to be  considered: one knows their birth time and location, or not:
  • If one knows their birth time and location, then one knows the accurate position of the Ascendant in the sky (for example: 10° in Aquarius). In this case, the chart has to be rotated until the Ascendant takes the 0° position, that is, 9 AM. The resulting birth chart is called a natural chart.
  • If one does not know their birth time and location, one cannot compute the accurate position of the Ascendant. In this case, the chart is rotated until the Sun reaches the 0° position, that is, 9 AM. The chart is then called a solar chart.

Why This Structure?

The center of the birth chart is the North Pole and one is watching towards the south. The top of the chart is Paris (at 12 PM). On the right (at 3PM), there is New York. On the left (at 9 AM), there is Tokyo. Since Japan is the land of the rising sun, the earth rotates anti-clockwise when you are at the North Pole. New York takes the Paris position, Paris takes the Tokyo position and Tokyo moves toward the New York position.

This explains why a chart is rotated until the Ascendant (or the sun) reaches the left (i.e. 9 AM) position of the chart. It is the rising position.

Relationship To Houses

The position of the Ascendant indicates the first house. Then, rotating anti-clockwise, we have the second house, third house, etc... For example, if one's Ascendant is in Leo, the first house would be in Leo. The second house would be Virgo, etc...

Correspondingly, each astral item is in a house, on top of being in a zodiac sign. For example, one says: "I have Pluto in the 3rd house".