One of the most interesting parts of astrology is learning about aspects planets form to one another as they're moving through the sky, or transiting, and how these planets affect the planets in your own individual birth chart.
There are many aspects in astrology, but the main ones are:
The Conjunction: This occurs when two planets are in the same sign and come within three degrees of one another. Conjunctions double the energy of that planet, so all the qualities associated with them will seem even more powerful.
The Opposition: This occurs when one planet is exactly opposite a particular planet or point in the chart. An opposition often feels like two forces pulling in opposite directions, and has the effect of dividing your focus.
The Square: Squares occur when one planet is 90 degrees away from another planet. They are considered challenging aspects because they feel like two forces that simply don't get along. One side wants what it wants now, and so does the other. Oftentimes, squares come about to give us challenges to overcome. This builds confidence over time.
The Trine: Trines occur when two planets are 120 degrees away from one another. This is considered a harmonious aspect because trines facilitate the exchange of energy, making it easier to meet new people, make more money, or achieve your goals. However, too much of a good thing can be detrimental, as you never have to overcome anything on your own or learn anything new.
The Sextile: A sextile occurs when two planets are 60 degrees from one another. Though slightly less strong then trines or squares, they also facilitate the flow of energy and are considered positive in nature.