The objective of this post is to put together the scattered information on making natal/birth charts at one place so that one may easily put this information to a better use, say making an astrology report software. Let’s get started.
This post discusses the astrological techniques to prepare a birth chart and gives you a basic understanding of how it’s all done. Here’s an introduction to astrology (pdf).
- A scientific calculator.
- Knowledge of trigonometric functions and properties.
- A paper and a pen.
- Background information on astronomy and solar system.
Let’s get familiar with the terms that would enable us in our goal.
Making a Birth Chart
Essentially, the following procedure is applied to make a birth chart.
- Calculate the local sidereal time of the person using his birth data (date of birth, time of birth and location of birth).
- Select a house system and calculate the house cusps.
- Calculate the positions of the planets at the given birth data.
- Place the planets in the houses and compute aspects.
- Interpret the chart.
So above we have outlined a basic procedure to erect a birth chart, but it’s not that simple, sometimes heavy math is usually involved making this 5 step procedure heavily cumbersome. But we’re here to help you, you can use one of the following approach and get it done.
Approaches to Prepare a Birth Chart
- Easiest – Use the online birth chart tools or freely available software.
- Somewhat easy – Use an ephemeris that will make this task very simple. One doesn’t need to touch complex math as it has already been taken into account. Chris Mitchell does a great job in explaining all this stuff.
- A bit tricky – Doing it by hand using formulae. If you’re all interested in learning the deeper things in astrology, the things that take place in the background and get to know the possibilities and limitations of astrology, take this approach. While it’s worth taking the trouble but really you’ll need to be good at math and astronomy. We discuss this approach in the rest part of this post.
An accurate time of birth, date of birth as well as location coordinates of birth place are required. Coordinates can be found in Atlas. Alternatively you may also download world atlas for programming purposes.
Calculate Local Sidereal Time
Sidereal time is what that is used in astronomy, we need to calculate the local sidereal time in order to get the mid heaven (or Medium Coeli). Online tools can be used to calculate sidereal time easily.
Selecting a House System and Calculating the House Cusps
Michael Munkasey has provided an excellent resource on house systems and formulae for calculating the house cusps.
Credit: University of Cambridge
Calculating the Planetary Positions
Here comes the major application of Kepler’s Law and Equations. David offers a nice starting point article and lays down concepts to calculate the planetary positions. However, we need a lot of data to do the calculations, so let’s look at the brilliant work by Paul Schlyter explaining how to compute planetary positions. He also offers an in depth tutorial with solved examples. (his work has been a main motivation behind this post). Please note the tutorial is much more elaborate than required in our case, we are only interested in ecliptic longitude and latitudes.
Computing Aspects and Drawing Chart
This part is what that brings life (and some sense) to all things we discussed above. A lot of literature is already available. Learn about zodiac (sun) signs and learn about planets. But before jumping to interpretations it becomes more important to learn the abstract meaning of astrological things we discussed above.
We hope this article serves its purpose and finds usage in modern astrology and software. Good luck!