An aspect is the angle between two planets in the sky. Half of astrological vocabulary grew out of that simple definition: trines, squares, oppositions, orbs, applying and separating configurations. Forecasts usually treat these words as ready-made labels — a trine is good, a square is bad. In reality an aspect has an exact minute, a measurable duration and mechanics you can follow, and all of it can be calculated yourself. Let us look at what actually happens up there.
What an aspect is technically
To understand the term, recall how astrology describes the sky. A planet's position is given by a single number — its ecliptic longitude, from zero to three hundred and sixty degrees. Zero is the point of the vernal equinox; from there around the circle: thirty degrees is the start of Taurus, sixty of Gemini, and so on.
An aspect is the difference between two such longitudes. If Mercury stands at a hundred and eighty-three degrees and Pluto at three hundred and three, the difference is a hundred and twenty degrees, and that is a trine. There is nothing mystical in the calculation itself: it is school arithmetic on two numbers.
Five angles are traditionally treated as major, and each comes from dividing the circle by a small whole number. A conjunction is zero degrees, planets at the same point. An opposition is a hundred and eighty, the circle halved. A trine is a hundred and twenty, the circle in three. A square is ninety, the circle in four. A sextile is sixty, the circle in six. Beyond them lie minor aspects — the semi-sextile, the quincunx, the sesquiquadrate — which not every school uses.
That division explains the familiar labels. Angles divisible by three, the trine and the sextile, connect signs of the same or compatible elements, and such combinations work in concert. Angles divisible by four, the square and the opposition, connect clashing elements: where one planet demands action, the other demands caution, and that is felt as tension.
The five angles and what each describes
An aspect describes not an event but a way two functions interact. A planet is a function: Mercury governs speech and thinking, Mars action, Venus attraction. The aspect says how the two relate at a given moment.
Conjunction — the same point, the functions merge into one. The strongest aspect and the most ambiguous: Sun with Moon gives a new moon, Mars with Saturn gives blocked action.
Sextile — sixty degrees, an opportunity. The key word is opportunity: a sextile does nothing on its own, it opens a window you may use or may never notice. Of all the aspects it is the quietest.
Square — ninety degrees, a conflict of tasks. Two functions demand opposite things and you have to choose. Squares are what usually move events along: where everything agrees, there is no reason to change anything.
Trine — a hundred and twenty degrees, agreement. The functions support each other, and whatever is done along that line meets no resistance. The flip side is that a trine does not compel action: the opportunity exists, the incentive does not.
Opposition — a hundred and eighty degrees, two functions facing each other. Always about balance between extremes, and almost always about another person: oppositions are easiest to notice when a living human plays the opposite side.
The orb: a tolerance, not a property
If only the exact angle counted, there would hardly be any aspects: the exact value exists for a single moment. Hence the orb — the permitted deviation. If Mercury and Pluto stand not at a hundred and twenty degrees but at a hundred and eighteen and a half, the aspect is treated as active with an orb of one and a half degrees.
The size of the orb is convention rather than physics, and schools disagree: commonly up to eight or ten degrees for conjunctions and oppositions, six to eight for trines and squares, four for sextiles, wider for the Sun and Moon.
From which follows something rarely stated: the orb is your choice of precision, not a characteristic of the sky. An astrologer working with an eight-degree orb will see twice as many aspects in a chart as one working with three. Both are formally right, but the first ends up with a chart in which everything connects to everything, and the second with only the sharpest links. That is precisely why two readings of one chart can diverge while both calculations are correct.
The practical guide is simple: the smaller the orb, the more noticeable the aspect. A quarter-degree orb feels like the background of the day; a seven-degree one is easier to miss than to feel.
Applying and separating: the distinction people skip
This is the most useful part of the subject and the rarest in popular writing. An orb says little by itself until you know whether it is growing or shrinking.
An applying aspect means the planets are approaching the exact angle and the orb is shrinking. The situation is ripening, the tension or the opportunity is building, the event lies ahead. A separating aspect means the point has been passed, the orb is growing, the influence is fading. Whatever was going to happen has happened.
The difference is enormous and the two look identical. Take two aspects from one week. On 12 September the Venus-Pluto square had an orb of about one and a half degrees and was applying: exact on 15 September at 05:21, so the theme was still sharpening. In the same days the Jupiter-Saturn trine had an orb of about three degrees and was separating: exact on 31 August at 23:54, and whatever it had to give, it had given. Judging by orbs alone, the second looks weaker only because the number is larger. The difference is direction, not strength — and a forecast that misses it will promise what has already passed.
How the exact moment is calculated
Here astrology briefly becomes astronomy, and this is the only part of the subject with no room for opinions.
You need an ephemeris model — formulas that return the ecliptic longitudes of the planets for any moment. Take the difference between two longitudes, subtract the angle you want, and find where the resulting function changes sign. Halve the interval, check which half holds the change, repeat until the interval is shorter than a minute. The method is called bisection.
That is how every moment in this article was obtained. Take the Mercury-Pluto trine on 12 September: at 13:22 the difference of longitudes is still slightly under a hundred and twenty degrees, at 13:24 slightly over, and at 13:23 exactly. You can verify it in any program that calculates positions rather than reading them from a table.
Two conclusions follow. First, the moment of an aspect is the same for the whole planet: it depends only on the time zone it is written in. 13:23 Moscow time is 10:23 GMT, but the event is one. Second, a calendar entry with no time is rounding rather than calculation — harmless for slow pairs, misleading for the Moon, whose aspects last hours.
Why some aspects last hours and others weeks
An aspect's duration is set not by its type but by the speed at which the difference between the planets' longitudes changes. The Moon covers about thirteen degrees a day, Mercury roughly one and a half, Jupiter and Saturn fractions of a degree. When a fast planet catches a slow one the orb changes quickly; when two slow planets meet it barely moves. Measured values for mid-September 2026:
| Pair of planets | Orb change per day | Time within a 1-degree orb |
|---|---|---|
| Moon — Sun | 12.7 degrees | about 4 hours |
| Mercury — Pluto | 1.7 degrees | about 28 hours |
| Venus — Pluto | 0.66 degrees | about 3 days |
| Sun — Mars | 0.35 degrees | about 6 days |
| Jupiter — Saturn | 0.27 degrees | about 7 days |
The spread runs from four hours to a week, and that is within one and the same sky. Hence a practical rule for reading forecasts: lunar aspects describe the mood of particular hours, aspects of the Sun and Mercury the tone of several days, and aspects of Jupiter, Saturn and the outer planets a background that holds for weeks and months.
Mixing these levels makes no sense, yet that is exactly what happens where a Moon-Mars square is delivered with the gravity of a Saturn-Pluto conjunction.
Five aspects in one week: a live example
Mid-September 2026 is convenient because within a few days the sky produced all five major angles, and each can be named to the minute. Times are Moscow time.
| Aspect | Pair | Exact moment | What it meant |
|---|---|---|---|
| Conjunction | Sun — Moon | 11 September 06:28 | New moon, the start of the lunar cycle |
| Trine | Mercury — Pluto | 12 September 13:23 | Clarity in conversation, the substance visible |
| Opposition | Mercury — Neptune | 12 September 19:28 | Promises sound better than they are worth |
| Sextile | Sun — Mars | 14 September 22:52 | A window of working energy |
| Square | Venus — Pluto | 15 September 05:21 | The theme of control in relationships |
Look at 12 September: two exact aspects of the same planet six hours apart, opposite in meaning. By day Mercury trine Pluto — a state in which the unsaid is audible and the cause easy to reach. In the evening the same planet opposite Neptune — the outlines blur and any statement seems wider and more pleasant than it is. One day, one planet, two opposite modes.
Such combinations are the real mechanics of daily forecasts. Not Mercury is favourable today, but the wording is precise until half past one and no longer precise after seven in the evening.
Retrogradation and aspects
One detail breaks the simple picture of planets circling and gradually converging. Planets periodically move backwards along the ecliptic — retrogradation, an optical effect of observing them from a moving Earth.
For aspects that means the same angle can become exact three times. A planet approaches the required degree and the aspect is exact the first time. Then it turns and passes the same point in reverse — the second time. Then it turns again and moves forward — the third. Several months can pass between the first and the third crossing.
Such cases are called triple aspects, and practitioners consider them the most substantial: a theme rises, is postponed, returns and closes only on the third pass. The Sun and Moon never go retrograde, so their aspects are never triple; Mercury, Venus and Mars do so regularly, and the outer planets spend nearly half the year retrograde.
Natal aspects and today's aspects
One word is used for two different things, and they are constantly confused.
Natal aspects are the angles between planets at the moment of your birth. They never change: a fixed picture describing how a person is built. A Mars-Saturn square in a birth chart means not an event but a property: effort comes through resistance, and stamina runs above average.
Transiting aspects are the angles between planets right now. They change constantly and describe the current background. Daily forecasts are about these.
The third case is a transiting planet aspecting a natal one — say transiting Saturn crossing the degree of your natal Moon. Astrology treats such moments as the most significant, because a general background meets a personal point, and for that reason they are individual.
Something practical follows. A daily horoscope by sign describes transits only — the sky shared by everyone. It cannot account for your chart, and promising otherwise would be dishonest. What it can give is background and timing: when an aspect is exact today and what is reasonable to do about it.
When several aspects come at once
Planets rarely form a single isolated angle. More often a figure emerges, and the stable combinations have names.
A grand trine — three planets, each trine the other two, a triangle within one element. Considered the easiest figure and the most passive: everything falls into place, and so there is no reason to exert yourself.
A T-square — two planets in opposition and a third square to both. The most workable of the tense figures: the third planet becomes the point through which the confrontation of the first two discharges.
A stellium — three or more planets in one sign or house. Not an aspect in the strict sense, but a configuration: one area of life takes disproportionate attention at the expense of the rest.
Daily forecasts hardly mention figures, and rightly so: they form rarely and hold for a long time, so they belong to the background of a year. But where a figure exists, it explains more than a list of separate angles.
What aspects do not do
Here it is worth being honest. An aspect is geometry, and the link between an angle in the sky and an event on the ground has not been demonstrated by any reproducible experiment. Everything astrology says about the meaning of aspects is centuries of practitioners' empiricism, not physics.
So a sensible attitude looks like this. The calculation is exact: the moment of a Mercury-Pluto trine can be verified, and it either matches the ephemeris or it does not. The interpretation is interpretation: it may help you look at a situation from another angle, but it is under no obligation to come true.
The practical benefit is real and not mystical. A forecast that names exact moments is checkable: you can see whether it matched. A forecast without figures is unverifiable in principle, which is why anything can be written in it. Telling one from the other is the only real protection a reader has.
How to check it yourself
Nothing special is needed. Any program that computes ephemerides shows planetary longitudes for a chosen moment; the difference between them is the aspect. If it is close to zero, sixty, ninety, a hundred and twenty or a hundred and eighty, the configuration exists — then determine the orb and the direction.
Direction is simpler still: look at the same difference a day later. Smaller means applying, the exact point ahead; larger means separating, the point passed.
On this site the calculations are done by our engine: it resolves planetary positions for any minute and finds aspect moments by stepping through time rather than reading tables. The same mechanics produced the void-of-course stretches, the new moon moments and the exact times in the daily horoscopes. A birth chart will show the aspects of your own nativity with their orbs — the same arithmetic, only applied to the sky at the moment you were born rather than to today's.
