How far an aspect departs from the exact measure.
A perfect trine is 120°: if two planets sit at 122°, the orb is 2°. The tighter the orb, the stronger the aspect is held to be — SideraMea marks this with the weight of the text. How much orb to allow before an aspect stops counting is a convention schools disagree on.
The orbs SideraMea uses
For the natal chart the site allows 8° for conjunctions and oppositions, 6° for squares and trines, and 4° for sextiles. These are close to the values most common in modern astrology: the aspects held to be strongest get a wider margin, while the lighter sextile gets a narrower one.
For transits the orbs drop to 3°, or 2° for the sextile. The moving planets form aspects to your chart all the time, and with wide orbs there would always be something to report, burying what matters. The orb also defines how long a transit lasts: it begins when the planet enters orb, peaks when the aspect is exact and ends when it leaves.
Applying and separating aspects
Two aspects with the same orb are not always equal. If the faster planet is moving towards the exact angle, the aspect is called applying: it is still building, and is traditionally read as the more active of the two. If the faster planet is moving away, the aspect is separating, and its effect is seen as fading.
The planets themselves matter too. Many schools allow wider orbs for the Sun and Moon, considered the most important points in the chart, and narrower ones for minor points. Others tie the orb only to the type of aspect, as in the values above.
Frequently asked questions
What orb should I use for aspects?
There is no single correct value. A common practice allows about 8° for conjunctions and oppositions, 6° for trines and squares, 4° for sextiles and tighter orbs for minor aspects. Some astrologers are more generous with the Sun and Moon. What matters most is staying consistent, so that charts can be compared with one another.
Does a wide orb make an aspect weaker?
Generally, yes. A near-exact aspect describes a very close link between two parts of you, one you are likely to feel often; an aspect at the edge of its orb is more of a nuance. So when reading a chart, start with the tightest aspects and treat the wide ones as background detail.
What is an out-of-sign aspect?
It is an aspect that works by degree but not by sign. Mars at 29° Aries and Venus at 2° Taurus are only 3° apart, so by orb they are conjunct, yet they sit in different signs. Many astrologers treat it as a genuine aspect that is simply less straightforward to read, because it blends the tones of two signs.
See it in your own chart
Calculating your birth chart is free: wheel, planets, houses, aspects and a first reading. All you need is your date, time and place of birth.