The aspects are the angles the planets make to each other in the horoscope, and also to the Ascendant, Mid-heaven, Descendant and Nadir. The aspects are measured by the angular distance along the ecliptic in degrees and minutes of celestial longitude between two points, as viewed from the earth.
They indicate focal points in the horoscope where the energies involved are given extra emphasis. The more exact the angle, the more powerful the aspect, although an allowance of a few degrees each side of the aspect called an orb is allowed for interpretation.
According to astrological tradition, they indicate the timing of transitions and developmental changes in the lives of people and affairs relative to the Earth.The traditional major aspects are sometimes called Ptolemaic aspects since they were defined and used by Ptolemy in the 1st Century, AD.
These aspects are the conjunction (approx. 0-10°), sextile (60°), square (90°), trine (120°), and opposition (180°).
It is important to note that different astrologers and astrological traditional utilize differing orbs (the degree of separation between exactitude) when calculating and using the aspects, though almost all use a larger orb for a conjunction when compared to the other aspects.
The major aspects are those that can be used to divide 360 evenly and are divisible by 10 (with the exception of the semi-sextile).
The following are the aspects in order of importance.
Conjunction 0° (orb ±8°).
The conjunction is a major point in the chart, giving strong emphasis to the planets involved. The planets will act together to outside stimulus and act on each other.
A conjunction is an angle of approximately 0-10°. An orb of approximately 10° is usually considered a conjunction, however if neither the Sun or Moon is involved, some consider the conjunction to be a separation (orb) of only about 0±08°. This is said to be the most powerful aspect, intensifying the effects of the involved planets mutually — and being a major point in the chart.
Whether the union is to be regarded as "positive" or "negative" depends upon what planets are involved: Venus, Jupiter and the Sun, in any possible combination, is considered the most favorable scenario , while the most unfavorable configurations involve Mars, Saturn, and/or the Moon . If the planets are under stress from other configurations, then the conjunction will be said to intensify the stress. When a planet is in very close conjunction to the Sun it is referred to as cazimi; when a planet is moderately close to the Sun, it is said to be combust. The Sun and Moon are in conjunction monthly during the New Moon(Amavasya).
Opposition (orb ±8°) is an angle of 180° (1/2 of the 360° ecliptic). An orb of somewhere between 5° and 10° is usually allowed. Oppositions are said to be the second most powerful aspect. It resembles the conjunction although the difference between them is that the opposition causes exaggeration as it is not unifying like the conjunction but instead exalted.
The opposition is indicative of tension, conflict and confrontation, due to the polarity between the two elements involved. Stress arises when one is used over the other, causing an imbalance; but the opposition can work well if the two parts of the aspect are made to complement each other in a synthesis.
Trine 120°(orb ±8°)
A trine is an angle of 120° (1/3 of the 360° ecliptic), an orb of somewhere between 5° and 10°. The trine indicates harmony and ease of expression, with the two elements reinforcing each other. The trine is a source of artistic and creative talent, but can be a 'line of least resistance' to a person of weak character. The trine has been traditionally assumed to be extremely beneficial.
Square 90°(orb ±8°)
A square (abrv. SQr or Squ) is an angle of 90° (1/4 of the 360° ecliptic, or 1/2 of an opposition [180°]). An orb of somewhere between 5° and 10° is usually allowed. As with the trine and the sextile, in the square, it is usually the outer or superior planet that has an effect on the inner or inferior one. Basically, the square's energy is similar to that of a trine but it is intensified to such an extent that the energy is said to be stressful. The square indicates frustration, inhibitions, disruption and inner conflict, but can become a source of energy and activation to a person determined to overcome limitations.
Sextile- Intermediate major/minor aspect
Sextile (orb ±6°) is an angle of 60° (1/6 of the 360° ecliptic, or 1/2 of a trine [120°]). A separation is considered a sextile. The sextile has been traditionally said to be similar in influence to the trine, but of less significance. It indicates ease of communication between the two elements involved, with compatibility and harmony between them, but only provides opportunity, requiring effort to gain its benefits. See information on the semisextile below.
Quincunx 150°(orb ±3°) The quincunx indicates difficulty and stress, due to incompatible elements being forced together. It can mean an area of self-neglect in a person's life (especially health), or obligations being forced on a person. The quincunx can vary from minor to quite major in impact.
Semisextile 30° (orb ±2°) Slight in effect. Indicates an area of life where a conscious effort to be positive will have to be made.
Semisquare 45°(orb ±2°) Indicates somewhat difficult circumstance. Similar in effect to semisextile.
Sesquiquadrate 135°(orb ±2°) Indicates somewhat stressful conditions. Similar to semisextile.
Quintile 72° (orb ±2°) Slight in effect. Indicates talent and vaguely fortunate circumstances.
144° (orb ±2°) Slight in effect. Indicates talent and vaguely fortunate circumstances.
A planet is retrograde when it appears to move backwards across the sky when seen from the earth, due to one planet moving more quickly relative to the other. Although it is not an aspect, some astrologers believe that it should be included for consideration in the chart. Planets which are retrograde in the natal chart are considered by them to be potential weak points.