The planets form angles to each other as they move along their trajectories. When they are 90 degrees apart, they form a square; 180 degrees apart creates an opposition and so on.
Most astrologers use five main aspects to determine how the planets communicate with and influence each other. Here are the five main aspects and their symbols on the charts.
Conjunction (0 degrees)
A conjunction means that the planets are working together in harmony. There is no tension here, especially if they share the same quality – ie. Venus and Moon work extra well together since they are both feminine.
Sextile (60 degrees)
This is also a favorable aspect. This links compatible elements, so that water is linked with earth, or fire is linked with air. Another harmonious aspect.
Square (90 degrees)
This means the planets are in conflict with each other; the least harmonious aspect. There is a lot of friction and the planets will challenge each other. Squares are often present in the personality of someone who is restless and at odds with themselves. But fear not, squares also show you potential for personal growth.
Trine (120 degrees)
Trines are usually formed by planets in the same element, so this is traditionally a harmonious aspect. However, these aspects tend to get boring, comfortable and even downright lazy. The problem is how to get the urges and needs presented operating.
Opposition (180 degrees)
This is not a favorable aspect as the planets are working against each other. For example, if Mercury and Pluto are in opposition, this means that your thought process can become your worst enemy as you are both quick-witted yet also deeply analytical. However, this aspect is not as bad as the square since here the planets can compromise with each other.