When a planet crosses into a new sign, it can create a whole new energy in the area that the planet governs.
Trines, 120-degree angles, are the most positive aspects in Astrology. When 2 planets are Trine, they are in the same element (Earth, Air, Fire, or Water), and they are working together in harmony. They can usually generate positive situations with no effort at all.
When planets are sextile, they are 60 degrees apart. Sextiles can bring positive outcomes, but only with some effort on our part.
A Quincunx is also sometimes called an Inconjunction. When planets are quincunx they are neither sharing the same element (Earth, Air, Fire, or Water) nor the same qualities (Cardinal, Fixed, or Mutable). That means there is nothing mutual for them to share, and the two planets will not function together. Quincunxes are actually minor aspects, and their influence is more subtle.
When two planets are conjunct, whether or not it will be positive or negative depends upon the planet. In most cases, it is negative, except when Venus or Jupiter are involved. Venus and Jupiter have a tendency to sweeten planets in this position.
When planets are at a 180-degree opposition, it usually brings challenges and conflicts. They will always be in the same element (Cardinal, Fixed, or Mutable). Occasionally an opposition can bring more of a reflection period, especially when the Moon is involved.
Squares are 90-degree angles, and they will also be of the same quality (Cardinal, Fixed, or Mutable) as oppositions. Squares can bring very difficult situations, especially when 3 planets line up in a T-square, or 4 planets align to make a grand cross. Expect conflicts when dealing with squares, especially when Mars, Saturn, Uranus, Neptune, or Pluto are involved.
When any planet is at its retrograde station (at the point of changing from a forward to a backward motion), it will cause difficulties depending upon the area that it rules. When Mercury, Venus, or Mars turn retrograde we watch the entire retrograde path, but the outer planets usually only influence us when they are at their stations.
Direct station is the point a planet reaches when it is ending its retrograde and in the process of changing from a backward to a forward motion. All planets can be difficult a few days before and after their direct stations.