One historical argument, many traditions
Ptolemy opens the Tetrabiblos by distinguishing the calculation of celestial motions from an inquiry into their supposed effects. His argument is evidence for a particular ancient approach to astrology, not a description of every tradition or a demonstration that its predictions work.
The distinction is useful when reading this atlas: a correctly calculated planetary position and a well-documented historical interpretation answer different questions. Neither makes the other automatically true.
Build a reading from an explicit question
Begin with the kind of question you want to explore. A birth chart, an event chart and a calendar conversion do not take the same inputs. Choose a system guide, open its tool, and review the requested date, place, time and convention before interpreting the result.
Keep a short reading record: the question; the inputs and their uncertainty; the calculated facts; the source or school used for meaning; and what remains unresolved. In a comparison, keep one such record for each tradition before drawing connections.
Worked reading example · an editorial exercise
Imagine a chart result displays a planet at 10° Taurus. First identify whether the label is tropical or sidereal. Next inspect the relevant house and aspects in the same configuration. Only then consult the chosen tradition’s explanation of that planet and placement. A sign label on its own leaves the method under-specified.
If the birth time is unknown, record that absence instead of selecting a time because its reading feels convincing. A useful question is “Which statements survive the uncertainty?” The answer may be narrower than the full chart.
Use the tree without flattening its branches
The wiki tree is a browsing aid. A shared word, symbol or numerical cycle does not by itself show historical influence. Follow the source trail for lineage claims, and consult a concept’s word origin separately from the history of the practice.
For personal reflection, treat a reading as an invitation to examine experience. For historical study, ask who wrote a rule and for which setting. For calculation work, ask whether another person could reproduce the output from the recorded inputs.
Word origin · etymology
Greek through Latin and French.
Greek astrologia joins astro-, star, with -logia, discourse or study. The word's historical scope overlapped with astronomy.
How we know · epistemology
Historical practice and testable claims
Historical texts establish what astrologers taught; they do not establish that its predictions work. Astronomical positions can be checked independently, while claims about personality or future events require tests that separate prediction from chance and hindsight.
Ptolemy: Tetrabiblos I.1–3, Robbins translation ↗Shawn Carlson: A double-blind test of astrology, Nature (1985) ↗
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Connected concepts
Read alongside this entry
Terms used in this explanation
Mentioned in 27 other entries
These links connect subjects and terminology. They do not establish a shared historical origin.
Sources & provenance
Use the citations beside each section to distinguish a calculation convention, a historical teaching and an editorial example.