In astrology, the distance between any two planets and zodiac signs is called an aspect.
What obstacles do you face when trying to grow and evolve? What will make it easier for you?
To find out, astrologers track the constant movement of the planets, and how each planet interacts with the others.
How the Aspects Express
Conjunction, O°, expresses through PROMINENCE.
The two planets in conjunction are blended together, fused, and intensified. Planets in conjunction must be interpreted as a blend in which the planets work together. This can be a good thing if the two planets get along (like say, Venus and the Moon), but it can be challenging if the two planets are incompatible (like say, Mars and Neptune).
Semisextile, 30°, expresses through GROWTH.
It is considered by some astrologers as mildly beneficial, but since it connects signs of different elements and qualities, it may actually be mildly difficult, awkward, or uncomfortable.
Sextile, 60°, expresses through OPPORTUNITY.
It represents an easy flow of opportunities or ideas that, if acted upon, will help realize the individual's goals. It can also indicate talents.
Square, 90°, expresses through OBSTACLES.
Traditionally, this is a negative, inharmonious aspect. The planets and houses involved are areas in the individual's life where adjustments must be made and where tremendous effort must be expended to realize gains. Squares can also signify where much tenacity and endurance is applied.
Trine, 120°, expresses through LUCK.
This is considered the most fortunate of aspects. The trine aspect represents easy flowing energy between the planets involved, bringing luck, opportunities, and innate creative talents. But even too much of a good thing can be bad at times because the ease brought on by the trine can sometimes be taken for granted, and the talents left unexpressed.
Inconjunct, 150°, expresses through EXPANSION.
It is not necessarily negative, but it brings strain, some difficulty, or stress. This can sometimes affect the health. It can indicate circumstances that are forced upon the person, or self-neglect regarding that area of life.
Semisquare, 45°, expresses through FRICTION
This aspect implies friction, generating minor internal conflict or frustration that can be annoying.
Opposition, 180°, expresses through SEPARATION.
This aspect indicates a fundamental polarity or duality; a situation in which one must cooperate with others or break with them. Compromise can be achieved by accepting that the two are parts of a whole.
Sesquisquare, 135°, expresses through AGITATION.
This aspect denotes the same friction as the semi-square, but this irritation tends to generate external difficulties (whereas the semi-square correlates more with inner conflict).
Parallel, O° declination, expresses through INTENSITY.
This aspect activates your ability to organize and reorganize some aspect of your life, depending on the planets and asteroids (or stars) involved.
An absolutely wonderful and detailed reference page is located on Cafe Astrology here: https://cafeastrology.com/articles/aspectsinastrology.html
Another can be found here: https://medium.com/@dreamingsouls/the-meaning-of-planetary-aspects-in-astrology-42ba16069ffa