One Reed Publications
Home Journal Maya-Aztec Report Books Articles Services Events Software Divination 2012 Links Contact Us

cover Astrological Chart Calculations: An Outline of Conventions and Methodology

by Bruce Scofield

Attention: the edition of Astrological Chart Calculations described below is now out of print. A new expanded edition, as a 6 x9 paperback of about 200 pages, is near the end of production and should be available in a few months. Watch for an announcement.

From the Introduction:

The material contained in this document has been assembled for the purpose of maintaining the tradition of casting horoscopes by hand in a meaningful way. With the advent of the computer, the mathematical skills and astronomical insights involved in chart casting have become endangered. Today these skills are being kept alive primarily by Kepler College and the requirements of certification exams such as those of the National Council of Geocosmic Research, the American Federation of Astrologers, and a number of small regional schools. While the computerized experience of astrology is certainly labor-saving, it bypasses information that explains how the astrological chart, now calculated in split seconds, came to be what it is.

Prior to the 20th century, astrological chart calculations were, for the most part, extremely cumbersome. Astrological textbooks of past centuries routinely included tables of trigonometric functions or logarithms, and much space would be devoted to problems like determining local time. Since primary directions were extensively used during most of the previous two millennia, astrologers were required to calculate the positions of the planets and house cusps against several frames of reference. What was called a speculum, a listing of each planet's longitude, latitude, right ascension, declination, oblique ascension, oblique descension, etc. was routinely calculated for each chart. Most of these supplementary positions required the use of trigonometry. This is the reason that so many ancient astrologers were mathematicians and vice versa. In fact, astrologers were routinely referred to as mathematicians in Rome and during the Middle Ages.

Astrological chart casting during the 20th century became more streamlined and far easier than in previous times. Time zones became standards against which birth times could be adjusted and ephemerides and tables of houses for various systems became widely available. With the rise of easy to calculate secondary progressions and solar arc directions as preferred predictive techniques, the need for trigonometry was eliminated. Most astrologers in the 20th century learned to calculate planetary positions using logarithms. House cusps (mostly Placidian because of availability) were simply interpolated from tables using proportions. When I learned how to cast a chart in the late 1960's, I used both logarithms and a slide rule. By the 1970's pocket calculators became a standard tool for chart calculations and the first astrological computers appeared. It was at this time that many of the older trigonometric formulae were revived by programmers anxious to produce software that would allow users to try out any technique they wished. By the mid 1980's very few astrologers were hand calculating charts. Most owned computers or were ordering charts from chart calculation services. Only the few who saw a value in passing an astrology exam continued to learn the relatively simple 20th century methodologies for chart casting.

At present many people have become successful in the field of astrology without ever having to add logarithms or interpolate a house cusp. Some argue that since astrology is primarily a counseling technique, knowledge of the "nuts and bolts" is irrelevant. Most of us drive cars or use electronic gadgets, but only a very few have any idea of how they work. We trust the repair of these things to the experts. I don't think that to be a good analogy, however. The astronomical features alone that lie behind the numbers and symbols in an astrological chart are profound clues to the function of certain features of the chart. Knowing why Aries rises more quickly than Libra, or how house systems differ are elements that add depth and insight into astrological interpretation. It's when the chart is seen as what it really is, a map of the sky at the time and place of birth, that the astrologer truly enters into the tangible cosmic environment that contains the information sought. Otherwise an astrological chart is nothing more than a scrap of paper decorated with symbols.

The material presented in this document is designed to teach both the method and the meaning of astrological chart calculations. It is hoped that this very ancient part of astrology, the mathematical ritual of preparing a chart, will allow students to not only glean deeper insights into horoscopy, but to also allow for a unique contact with astrology's long history.

Table of Contents
Introduction 3
Section I: Astronomical Frames of Reference
        The Earth in Space 4
        The Earth Quantified  6
        Definitions of Points on the Celestial Sphere 8
        Time 9
        Definitions of Time Conventions 11
        Time Space Conversions 13
        Mathematics for Chart Calculations 13
        Trigonometry 15
        Logarithms 16
        Systems of House Division 18
Section 2: Calculating the Astrological Chart
        Required Materials 24
        Steps in Casting an Astrological Chart 25
        Worksheets for Calculations 28
        The Houses: Framework of the Chart 37
        Calculation of the planets'longitudes 38
        Calculating a Horoscope using a calculator 
        (with trigonometric functions)
        Other Astrological Chart Calculations 52
        Additional Sources on Astrological Calculations 55

One Reed Publications - (c) 2001

 8.5 x 11, paper, 60 pages, spiral-bound

 $17.00 + $1.75 postage