What is an aspect in astrology?

By Ines Vasquez

An aspect is the angle between two planets as seen from Earth, measured in degrees along the zodiac. Two planets 90 degrees apart are in a square; 120 degrees apart, a trine. Astrologers read certain angles as meaningful relationships between what the two planets represent, and the rest as no relationship at all.

How is an aspect measured?

An aspect is a measured angular distance. Take the zodiac as a circle of 360 degrees, place each planet at its position along that circle, and subtract one from the other. The result is the aspect. A planet at 4 degrees of Aries and a planet at 6 degrees of Cancer are 92 degrees apart, which counts as a square — close enough to the exact 90 to be read as one.

The geometry is straightforward and not in dispute. What astrologers add is the claim that some of these angles matter and some do not, and that the ones that matter carry different qualities. A 90-degree angle is read differently from a 120-degree angle. A 100-degree angle is, in most traditions, read as nothing.

That selectivity is the whole basis of aspect doctrine. The angles held to be significant are the ones that divide the circle by small whole numbers: 360 divided by one, two, three, four and six. This is a Greek idea about harmony, carried into astrology from music theory and geometry, and it is why the traditional aspects are sometimes called the Ptolemaic aspects after Ptolemy, who set them out in the Tetrabiblos in the second century.

What are the five major aspects?

These five are the aspects every tradition uses, ancient and modern, and they are the ones to learn first. Each has its own page on this site, because each is read with enough nuance that a row in a table does not cover it.

Strictly, Ptolemy treated the conjunction as a different category — a co-presence rather than an aspect, since two planets in the same place are not looking at each other from a distance. Most modern practice has folded it in and calls it an aspect anyway. The distinction still surfaces in traditional work, where writers are careful about whether a planet "beholds" another or is simply with it.

Why do some angles count and others do not?

Because the significant angles divide the circle evenly, and the tradition inherited a conviction that even division means relationship. Ptolemy argued it from the ratios that produce concordant musical intervals: the octave, the fifth, the fourth. An angle that does not correspond to a simple ratio was held to produce no connection between the planets, the way two notes with no common ratio produce no chord.

The same logic explains why the aspects group by number. The divisions by two and four — opposition and square — belong to a family the tradition read as hard, effortful, productive of events. The divisions by three and six — trine and sextile — belong to a family read as soft, easy, sometimes too easy to notice. That pairing of number with quality is ancient, and it is one of the places where astrology's own reasoning is visible rather than merely asserted.

There is a further ancient layer that modern practice has largely dropped. Aspects were originally understood through the signs, not through degrees: two planets were in square if they sat in signs three apart, regardless of how many degrees separated them exactly. This is whole-sign aspect doctrine, standard in Hellenistic astrology and in Vettius Valens around 150 AD, and it has been revived since the 1990s by astrologers working in the Hellenistic reconstruction. Degree-based aspects with tolerances came later and now dominate. Both are in use, and they sometimes disagree about whether an aspect exists at all.

What are the minor aspects?

Minor aspects are further divisions of the circle, held to work in the same way as the major five but more faintly. The commonly used ones:

The semi-square and sesquiquadrate come from Johannes Kepler, who in the early seventeenth century extended aspect doctrine by continuing the logic of division past where Ptolemy stopped. The quintile family is also Kepler's. The quincunx was in use earlier but was treated as a non-aspect by most Hellenistic writers, since signs 150 degrees apart share neither element nor gender nor mode — they have, in the older language, nothing in common.

How much weight to give minor aspects is a real disagreement. Twentieth-century astrologers working in the harmonic tradition, notably John Addey and later David Hamblin, built entire systems on further divisions. Traditional practitioners tend to use the five Ptolemaic aspects and nothing else, on the grounds that the minors were never part of the technique the tradition was actually tested with. A reader looking at a chart report full of biquintiles is looking at a modern editorial choice, not a consensus.

How close does an aspect have to be?

Within a few degrees, and how many degrees is a matter of judgement rather than rule. The allowance is called the orb. A square with an orb of 8 degrees is counted as a square anywhere from 82 to 98 degrees.

Common practice gives wider orbs to the Sun and Moon than to the other planets, wider orbs to major aspects than to minor ones, and tighter orbs when precision matters. Figures between 6 and 10 degrees for the majors and 1 to 3 degrees for the minors are typical, but astrologers vary, and some work only with exact-degree aspects and ignore everything else.

An aspect also has a direction. If the faster planet is moving towards the exact angle, the aspect is applying; if it has passed it and is moving away, the aspect is separating. Traditional astrology treats this as significant — an applying aspect is a thing still coming, a separating one a thing already done — and it matters most in horary, the branch that answers specific questions from the chart of the moment they were asked. Orbs and application are worked through in more detail on the page covering them.

What do astrologers do with aspects?

Aspects are read as the connections between the parts of a chart, which is to say they are where interpretation stops being a list and becomes a pattern. A chart with Venus in Taurus and Saturn in Aquarius is two separate statements. A chart where those two are in square is one statement, and the tradition reads it as a relationship between what Venus signifies and what Saturn signifies — in modern practice, something about affection meeting restriction.

That way of reading is largely twentieth century. Traditional astrology used aspects primarily to determine whether a planet could act, and on what: an aspect was a channel of influence, and its condition told you whether the influence arrived helped or hindered. The psychological reading — aspects as internal tensions, the chart as a portrait of a mind in conflict with itself — enters through Dane Rudhyar in the 1930s and becomes standard after Liz Greene's work in the 1970s. The question has not been resolved and may not be resolvable, often in the same paragraph on the same website, and they are not the same claim about what a chart is.

Aspects also operate in time. When a planet in the sky today forms an aspect to a planet's position in a birth chart, that is a transit, and it is the main technique modern astrologers use to say anything about a particular period. The angle is the same geometry; what changes is that one of the two positions is fixed at birth and the other is moving. The recurrence people notice — that a difficult stretch feels oddly like a stretch from three years ago — is usually a transit returning to the same natal point, or a different planet arriving at the same angle.

What is an unaspected planet?

A planet that makes no major aspect to any other planet in the chart, within whatever orb the astrologer is using. It is uncommon but not rare.

Modern astrologers read an unaspected planet as operating without moderation from the rest of the chart — the function it represents running on its own terms, sometimes strongly, sometimes erratically, and generally hard for the person to see themselves. That reading is twentieth century and comes out of the psychological tradition; there is no classical doctrine of the unaspected planet in Ptolemy or Valens, though Hellenistic astrology has related ideas about planets that are feral or in aversion to the significant points of a chart.

Whether a planet counts as unaspected depends entirely on orb choice and on whether minor aspects are admitted. Widen the tolerance by two degrees, or allow the semi-sextile, and the same planet is aspected. It is a useful reminder that the geometry is fixed and the doctrine built on top of it is not.

More in The aspects

• What does a conjunction mean in astrology?
• What does an opposition mean in astrology?
• What does a square mean in astrology?
• What does a trine mean in astrology?
• What does a sextile mean in astrology?
• What is an orb in astrology?
• All of Learn