What is an aspect in astrology?
An aspect is the angle between two points on the zodiac wheel. Between sun signs it is counted in whole signs of 30°: four apart is a trine (120°), two apart a sextile (60°), three apart a square (90°) and six apart an opposition (180°). The machine measures these angles for the compatibility section of its card.
Planets that look at each other
Aspect comes from the Latin aspicio, to look at. Before the word existed, astrologers said that planets saw, regarded or witnessed each other. The idea is geometric: divide the circle by two, three, four or six and you get the angles that count. 1
The five classical aspects are the conjunction (0°, the same place), the sextile (60°), the square (90°), the trine (120°) and the opposition (180°). Ptolemy called the trine and the sextile harmonious and the square and opposition disharmonious, reasoning from whether the signs involved share the same gender in his masculine–feminine split. 1,2
Signs or degrees
There are two ways to count. By sign, any two planets in Aries and Leo are in trine because the signs are four apart. By degree, they only count if the angle is within a few degrees of 120°. That allowance is the orb: modern astrologers commonly allow about 8° for conjunctions and oppositions and less for sextiles, with extra room when the Sun or Moon is involved. 1
Sun-sign compatibility is the sign-based version: it only asks how many signs apart two sun signs are. A full chart comparison works with degrees and every planet.
Minor aspects
Johannes Kepler, who practised astrology as imperial mathematician, added the quintile (72°), bi-quintile (144°) and sesqui-quadrate (135°) on geometric grounds. Modern astrologers also use the semi-sextile (30°) and the quincunx (150°), signs one and five apart, which Ptolemy counted as no aspect at all. 3,2
How the machine measures them
Calculated facts only, worked out the same way the machine does it.
- Between sun signs, the machine counts how many signs apart they are, the short way round the wheel, from 0 to 6.
- 0: the same sign (0°). 1: semi-sextile (30°). 2: sextile (60°). 3: square (90°). 4: trine (120°). 5: quincunx (150°). 6: opposite (180°).
- In the birth chart it measures degrees, with orbs of 8° for conjunctions and oppositions, 7° for trines and squares and 5° for sextiles, plus 2° when the Sun or Moon is involved.
- Ptolemy’s Tetrabiblos (2nd century AD) counts the same five classical aspects between signs: the conjunction, the sextile, the square, the trine and the opposition.
Where the idea comes from
Era by era, with sources. More in the Reading Room.
- Classical2nd century CEPtolemy sets out the aspects and their harmony or discord in the Tetrabiblos. 2,4
- MedievalMiddle AgesThe Latin word aspectus comes into use; earlier writers said planets 'beheld' each other. 1
- 1600sEarly 1600sKepler, imperial mathematician in Prague, proposes new aspects, including the quintile, from geometry. 3
Common misconceptions
“Square and opposition aspects are bad.” Astrologers read them as tension, which can drive things as much as block them. Ptolemy's labels were about harmony, not luck. 2
“Signs next to each other get along.” Neighbouring signs share no classical aspect; Ptolemy called them disjunct. 2
Questions people ask
What is an orb?
How far from exact an aspect may be and still count, usually a few degrees. 1
Is a conjunction an aspect?
Strictly, traditional texts distinguish it: the planets meet in one place rather than look at each other across the circle. 1
Which aspects matter most?
Most astrologers weigh the five classical aspects above the minor ones.
Sources
- Aspect, Skyscript, Glossary of Astrological Terms (Deborah Houlding). Read on .
- Ptolemy, Tetrabiblos, Book I, chapters 10–19 (aspects, houses of the planets, triplicities), LacusCurtius, University of Chicago (Loeb Classical Library translation by F. E. Robbins, 1940). Read on .
- Johannes Kepler, Skyscript, Glossary of Astrological Terms (Deborah Houlding). Read on .
- Ptolemy (by Alexander Raymond Jones), Encyclopaedia Britannica. Read on .