In modern astrology, there are four main basic building blocks one needs to understand in any branch of astrology: signs, planets, houses, and aspects. This post will specifically be about aspects in general. There will be separate posts about the major aspects themselves.
So what are aspects? Aspects are the connections planets have with each other depending on the sign and location they are in on the chart. It is essentially the relationships and conversations your planets have with each other.
Note: Degrees will show you the exact location of anything in astrology. Understanding degrees is important in understanding aspects.
The aspects in your natal chart is one of many ways to find that your planets in your natal chart are not just independent and autonomous celestial bodies. There are five major aspects in astrology: the conjunction, opposition, sextile, trine, and square.
The aspects can be understood as harmonious or disharmonious. By looking at aspects alone, trines and sextiles are harmonious while squares and oppositions are disharmonious. Conjunctions are neutral.
The strengths of aspects will also vary. Conjunctions and oppositions are often stronger than squares, sextiles, and trines. Due to this, the general orbs for conjunctions and oppositions are higher while the orbs for trines, squares, and sextiles are lower.
Orbs are a mathematical leeway when an aspect occurs. For example, a conjunction is when two planets are 0 degrees of each other. However, with orbs, a planet can be up to 10 degrees away from another planet and it would still be a conjunction, depending on your system of orbs. The existence of orbs argues that the effects of aspects do not have to be numerically exact, but its strength will increase as the planets come closer to a numerically exact aspect.
One common question is: What are the right orbs for each aspect? In various branches in astrology, the orbs will often change. For example, natal astrology will often have larger orbs than predictive astrology. Also, orbs are often personally determined by you. Find or create an orb system that works for you. Here is my personal orb system for reference:
Natal astrology
Conjunctions - 10 degree orb
Oppositions - 8 degree orb
Sextiles, squares, trines - 4-6 degree orb
Predictive astrology (transits)
Conjunctions - 5 degree orb
Oppositions - 3 degree orb
Sextiles, squares, trines - 2 degree orb
Another way to understand aspects generally is how they are formed. Planets will move counterclockwise in a chart, their movements creating aspects since some planets move faster than others.
When an aspect is moving closer to an exact aspect, it is applying. When an aspect is moving away from an exact aspect, it is separating. The orb of an aspect will gradually decrease with applying aspects and will gradually increase with separating aspects.
Astro.com will show you whether an aspect is applying or separating and will also show you whether the aspect is greater or less than the exact aspect.