Aspect Orbs Explained

An aspect is a particular angle between two bodies measured along the zodiac: 0° for a conjunction, 60° for a sextile, 90° for a square, 120° for a trine, 180° for an opposition. Two bodies are almost never at the exact angle. The orb is the difference between the measured angle and the exact one, and the orb rule says how large that difference may be for the aspect to be listed at all.

One worked aspect

Demonstration birth: 1991-09-06 at 18:30 local time, Kyiv, Ukraine (50.4501° N, 30.5234° E), Europe/Kyiv at UTC+3, so 1991-09-06 15:30 UTC. Tropical zodiac, Placidus houses, Swiss Ephemeris 2.10.03. Full result and settings on How to verify your birth chart.

The measured angle is the shorter way round the circle between the two longitudes, always between 0° and 180°. Here it is 120.55°, which is 0.55° away from the exact trine at 120°. The natal rule allows 8° for a trine, so the chart lists Sun trine Neptune with an orb of 0.55°. Had the same pair been 8.05° from exact, nothing would be listed, even though the physical separation is almost the same.

The rules NatalChart.AI applies

Only the five major aspects are calculated in every mode. Minor aspects such as the quincunx, semi-sextile or quintile are not listed. The allowed orb depends on what is being compared.

Natal chart

Synastry (one chart against another)

Transits to the natal chart

Transit orbs are tighter because the sky keeps moving: a contact that is within 2° of exact is one that is happening now, not one that will be exact next month. The same principle applies to the transit readings and to the weekly horoscope, which is built from these contacts.

What the rule changes

The demonstration chart lists 49 aspects under the natal rule. The tightest is Pallas square Juno at 0.21°; the widest is Moon square Ceres at 7.95°, still inside the rule. If the tighter synastry orbs were applied to the same natal pairs, 35 of the 49 would remain. Nothing in the sky differs between the two lists; only the threshold does.

This is why two charts of the same birth can show different aspect lists and both be correct. Before treating an extra or missing aspect as an error, compare the orb rules and the set of bodies each tool includes. NatalChart.AI compares 17 bodies in the natal chart: the ten planets, the true node, Chiron, Lilith and the four asteroids Ceres, Pallas, Juno and Vesta.

Applying and separating

An aspect is applying when the orb is closing, so the bodies are moving toward the exact angle, and separating when the orb is opening. The direction depends on the motion of both bodies, not on which is faster in general: a retrograde body moves backwards through the zodiac, which can turn an aspect that would normally be applying into a separating one, or the reverse. The only reliable way to judge it is to compare the measured angle at two moments.

NatalChart.AI does not compute applying or separating; the chart reports the orb of each aspect and nothing about its direction. For the worked example the listed speeds allow a check by hand: the Sun moves 0.9704°/day and Neptune -0.0104°/day (retrograde). One day later the measured angle would be about 119.57°, so the angle is moving toward the exact 120° at about 0.98° a day: the trine is applying at the birth moment and, at that rate, would become exact about 13 hours later. That estimate assumes constant speeds and is not part of the product’s output.

Reading an aspect with its orb

• Name the aspect and the orb together: “Sun trine Neptune, 0.55°” says more than “Sun trine Neptune”.
• Treat a contact near the limit of the rule as weaker than one near exact; the rule only decides whether it is listed.
• When two tools disagree, check the orb rules, the bodies compared and the zodiac before anything else. See how to verify your chart.

Questions

Next: Aspects in astrology · Verify your chart · Transits to your chart · All calculators