The energy of any one planet or planets in the position they rent in zodiac houses are also affected by how the planets are positioned with respect to each other at any time. This is the conversation, if you will, that takes place that influences the effect on the person's chart. Some positions produce arrangements that reinforce these positive energies. While others bring about disruptive and difficult effects. The relationship between the planets are called Aspects. They refer to the ANGLE or degree the position describes.
The major aspects are: conjunctions, oppositions, squares, trines
and sextiles.
  • When any two planets are in the same sign of the zodiac, and 10 degrees or less apart, they are in Conjunction.
  • If any two planets are opposite each other in the zodiac, then they are in Opposition. 
  • If any two planets are at 90 degree angles (or right angles) to each other then they are Squared.
  • When any two planes are at 60 degree angles to each other, then they are Sextile.
  • When they are 120 degrees apart they are Trine.
The effect of an aspect between two planets is strongest when the fastest planet reaches the exact angle of the aspect. However effects can be felt over several degrees (called the orb), depending on which planet is involved and on whether it is a major or a minor aspect.   
     The interpretation of aspects is based impart on how the planets fall into signs with similar or conflicting elements and qualities. For example, the square aspect has planets in the same quality or mode, but conflicting elements (e.g., fire and water) while the trine aspect the planets are in the same element, but stimulated by different qualities.   
     The aspects are described as harmonious or inharmonious. Harmonious aspects can help matters along. Inharmonious aspects ("badly" aspected planets) introduce stresses, many of which can actually help you if you learn to deal with them. A brief description of the meaning of the major aspects is as follows:
  *Note: in determining the aspect an astrologer counts SIGNS between the two planets and NOT houses. This is particularly important when dealing with a chart that has an intercepted house or sign.
These are the Major Aspects:
conj Conjunction (10 degrees or less)
Keywords: Emphasis, Intensity

A conjunction occurs when two planets are from 0 to 7(or 10) degrees of each other. Their energies combine or reinforce each other, giving emphasis to the planet's expression. A conjunction can be favorable or unfavorable depending on the planets involved and whether or not these planets are harmonious or opposite in character.  This aspect merges and intensifies the energies of two planets. Inner tension can arise if the planets have conflicting natures.

  op Opposition (180 Degrees)
Keywords: Cooperation, Awareness

An opposition is an unfavorable, major aspect in which two planets are 180 degrees apart, plus or minus 7 degrees (173-187 degree orb). An opposition indicates areas where there is a need to balance opposing forces or circumstances. Through an opposition, you have an opportunity to gain greater awareness of yourself as well as others. Sometimes these forces can't be resolved and the only solution is to compromise. Since the conditions represented by an opposition can't be changed, they must be dealt with or accepted as they are.   Inharmonious aspect creating inner tensions between your planetary urges. It also creates dynamic tensions with others, which you must reconcile if you want to maintain harmonious relationships

sq Square (90 degrees)
Keywords: Challenge, Obstacle
A square is considered to be a major, unfavorable aspect in which the planets involved are 90 degrees apart, plus or minus 7 degrees (83-97 degree orb). In this aspect, the energies of the planets are clash with one another, each trying to make the other to conform to it's manner of expression. Squares in a chart indicate where you will need to apply effort and determination to achieve your goals.       Inharmonious aspect causing tensions and obstacles for you to overcome. It forces you to choose between your conflicting inner needs and urges. 
Squares signify action: in the Cardinal squares this action is swift; in fixed squares, the action is gradual and cautious and in mutable square, the action is changeable and influenced by other factors.

tr Trine (120 degrees)
  Keywords: Harmony, Easy Luck

A trine is a major, favorable aspect in which the planets involved are 120 degrees apart, plus or minus 7 degrees (113-127 orb). The trine represents harmony, creative inspiration and generosity. Trines in a chart can help a person to overcome difficulties and it's influence can bring good luck and easy attainment; also indicates where things come with little effort. It also identifies natural talents and where success is most easily attained.  Harmonious aspect that brings the two energies into an easy interplay. This can create such beneficial consequences that things become to easy for you and you become lazy.

se Sextile (60 degrees)
Keyword: Opportunity
A sextile is considered to be a major, favorable aspect in which two planets are 60 degrees apart plus or minus 5 degrees (55-65 degree orb). The planets involved are of the same in gender, quality, and functions harmoniously. Sextiles in a chart show where opportunities are presented in life. They represent circumstances that when acted upon can lead to achievement and success of a goal.  Harmonious aspect that helps energies flow toward attainment of your goals, provided you make some conscious effort to achieve them yourself.

These are Minor Aspects:
ss Semi-Sextile (30 degrees)   Keywords: Cooperative, support
A semi-sextile is a minor, favorable aspect in which two or more planets are 30 degrees apart plus or minus 3 degrees (27-33 degree orb). This aspect is of mixed quality - for the planets involved will be in inharmonious signs. The planets will support each other in an external sense, but won't share any true inner communication. However, the expression of a semi-sextile indicates that one must give attention to contrasting energies so that each functions effectively. 
It is similar to sextile but minor, It also can mitigate other inharmonious aspects.

sq Semi-Square (45 degrees)
  Keyword: Friction

A semi-square is a minor, unfavorable aspect in which the planets involved are 45 degrees apart plus or minus 3 degrees (42-48 degree orb). The semi-square is similar to a square, but the influence is only a minor frustrating aspect.  This causes friction and irritation between planets in aspects. This causes mild stress and tension.

qq Quintile (72 degrees)
Keyword: Creativity

A quintile is considered to be a minor, favorable aspect in which two planets are 72 degrees apart plus or minus 5 degrees (67-77 degree orb). The quintile is an aspect that represents self-expression, creativity, and fulfillment of personal potential.

se Sesqui-quadrate (135 degrees)
Keyword: Agitation

A sesqui-quadrate is considered to be a minor, unfavorable aspect, where the planets involved are 135 degrees apart, plus or minus 3 degrees (132-138 degree orb). It's influence basically represents minor obstacles that are more of an agitation than a serious problem. The sesqui-quuadrate is also similar to a square.  This causes irritation, aggravation and discord.

qq Quincunx (Inconjunct)
          (150 Degrees)
Keywords: Growth, Adaptation

A quincunx is considered to be a minor, unfavorable aspect, where the planets involved are 150 degrees apart, plus or minus 3 degrees (147-153 orb). This is probably the most important of the minor aspects. This aspect indicates problems that you need to learn to adapt to or to work around; which in turn will lead to personal growth. Usually the planets and signs are totally unrelated to each other and don't share the same element, quality or gender. Since they have little in common, it is difficult to harmonize their energies. There is a perception of slight tension that is hard for the conscious mind to grasp. This aspect calls for a change in attitude and of old routines. It indicates the necessity to adjust to the conditions as shown by the planets and houses involved.   This aspect is another minor inharmonious one. It suggests a need for adjustment.

Unaspected Planets
An unaspected planet is a very powerful focal point and usually means that the individual is very aware of the planet's influence but may not be able to integrate it's qualities psychologically into the personality. Sometimes psychological problems can result and in such cases, professional help is recommended.