Horoscope Compatibility Basics: Planets, Signs, Houses and Aspects in Synastry

Horoscope compatibility or synastry is one of the hottest topics in astrology and justifiably so. Relationships are perhaps our most complex engagements. Yet through astrological symbolism, we can see a map of the relationship between two people, the intricate workings of each individual’s personality and the various ways they connect with each other. Have a look at birth chart compatibility and the symbols used in it. You can also refer to a more general introduction to astrological chart comparison.

What Is a Horoscope Love Compatibility Chart and How Does It Work?

Synastry or horoscope compatibility is the comparison of the astrological natal charts of two persons in a relationship, or potential relationship. While astrologers use various types of charts to analyze the subject, synastry is the most commonly used.

In synastry, you:

  1. Study the characteristics of each individual chart to assess the owner’s needs and personality
  2. Compare the zodiac signs of the planets in one chart with that of the other (e.g. Venus in Libra for the husband and Venus in Cancer for the wife)
  3. Measure the aspects that the planets of one chart make to the other
  4. Find the house overlay positions of one partner’s planets within the other partner’s chart (e.g. his Mercury in Virgo in her eighth house)
  5. Make an assessment of the relationship based on these factors combined


As you may understand from the above, synastry assumes knowledge of natal astrology and how to interpret the planets, zodiac signs, houses and aspects.  It is also helpful to be familiar with forecasts, called transits, because comparing two charts in synastry is like comparing a natal chart to a transit (forecast) chart. In other words, if your partner’s Mars is in your fourth house and makes an aspect to your Jupiter, it is like having a Mars transit in your fourth house and aspecting your natal Jupiter.

The Basic Symbols of Chart Comparison

So to be able to judge compatibility, you must understand at least the most basic elements of astrology charts, namely the planets, signs, houses and aspects. Knowing what these principles mean allows you to interpret and compare charts yourself without the need of an astrologer. Even if you do not want to practice astrology yourself, knowing the fundamentals makes it easier to read an astrology reading such as a compatibility report for yourself and/or a loved one.

Those who want to become professional astrologers must of course, get certified by a reputable body. To give counseling, you must also learn to do professional relationship counseling. Do not attempt to teach other people about their lives just by reading a book or Internet article!

Below are brief summaries of the meanings of the planets, signs, houses and aspects in birth charts and in synastry.

Zodiac Signs in Synastry

The zodiac signs are types of energy originating in the four elements: fire, water, air and earth. The zodiac signs determine how the planetary principles are experienced. The zodiac signs are important in determining horoscope compatibility.

  • Aries is action-oriented and likes to take initiative. In synastry, planets in Aries are self-assertive and quick to act, often impulsive. Those with a prominent Aries are self-reliant. In relationships, they want to be able to speak up and take action for themselves. They cannot stand idleness.
  • Taurus is self-preserving and acquisitive. In synastry, planets in Taurus are slow to express themselves, yet are steady and resourceful. For example, Mars may be slow to anger but once provoked, the resentment lasts. People with a strong Taurus are possessive and territorial. Material security is of utmost importance to them. Change is a scary thought.
  • Gemini is curious and mentally agile. In compatibility, planets in Gemini are changeable and restless. Those with a strong Gemini are eager to connect with people and ideas. They need lots of social and intellectual stimulation.
  • Cancer is nurturing and protective. In synastry, planets in Cancer are sensitive, defensive and moody. A person with a dominant Cancer seeks a safe familiar environment and strong emotional bonds.
  • Leo is radiant and warm. Planets in synastry in Leo are dramatic, eager for attention and have a sense of self-importance. When this sign is strong in a person, they need to be the center of attention in a relationship, or at least feel very special.
  • Virgo is analytical and helpful. Planets in Virgo in synastry are markedly discriminating, critical of self and others, but eager to help. A Virgo type of person tries to rationalize feelings and needs a sense of order in a relationship. It cannot stand chaos.
  • Libra is diplomatic and idealistic. Planets in Libra in synastry show refinement and consideration for others. Those with Libra predominant have a strong sense of fairness and justice, as well as a strong desire for a committed partnership.
  • Scorpio is intense and compulsive. In synastry, planets in this sign are controlling, secretive and magnetic. People with a strong Scorpio seek deep transformation through their relationships. They despise superficiality.
  • Sagittarius is adventurous and idealistic. In synastry, planets in this sign are freedom-loving, tolerant but perhaps impatient and self-righteous. Those with a strong Sagittarius need freedom to explore physically and spiritually. They are restless and may not want to stay in the same place for too long.
  • Capricorn is responsible and ambitious. Planets in this sign in compatibility are hardworking and serious. A Capricorn type of person wants to find success with their partner.  It could be ambition in a positive sense or a mere social climber.
  • Aquarius is impersonal and independent. Planets in synastry in this sign tend to be eccentric, brilliant and detached. Aquarius types of people cling to their views and ideals. Their sense of security is often bound up with a group who share their ideals rather than with a single partner.
  • Pisces is fluid and compassionate. Planets in synastry in Pisces are mystical, elusive and formless. Piscean types seek oneness with their partner, and are emotionally vulnerable.

Synastry Planets

Planets in synastry are like various representatives of the same person. The planets represent dimensions of the multi-faceted being that is man. How those dimensions are lived is influenced by other astrological factors such as the elements, zodiac signs, houses and aspects. In compatibility, aspects between two individuals’ planets show how they relate to each other.

  • Sun is the ego and vitality. Its zodiac sign position in the birth chart is the basic energy type of the individual. What motivates him or her and what he or she identifies with. Aspects to the sun affect one’s vitality and ability for self-expression. In horoscope compatibility, the sun is the energy and drive you bring to a relationship. If you are able to fully express your sun sign, you feel strong in the relationship. See also the sun in the zodiac signs and houses.
  • Moon is the instinct and emotions. The zodiac sign position shows what that person needs to feel secure and comfortable, what feels familiar and gives inner tranquility. Aspects to the moon color how you feel about yourself, how you express your emotions and how you react to your experiences. In synastry, it is necessary to nourish the moon to feel secure in the relationship. Read more about moon signs compatibility.
  • Mercury is how a person thinks and communicates. The zodiac sign shows how well that person articulates feelings and thoughts, how they give and receive information. Mercury is important for communication in synastry.
  • Venus is love and social graces. The zodiac sign tells us how a person shows affection and how he or she prefers to get close to others and be appreciated by them.  It also shows our values in the material, emotional and mental sense of the word; that is, whatever we cherish.  Venus is key in synastry. It is obviously crucial in a marriage and other kinds of relationships.
  • Mars is will, energy and courage. In synastry, the Mars zodiac sign shows a person’s aggressive side. It shows how the native expresses physical and sexual energies. Mars is how a man expresses himself as a lover.
  • Jupiter is self-confidence, faith and abundance. The zodiac sign describes the types of experiences that one needs to have faith and be optimistic. In synastry, Jupiter shows where and how you can benefit and support your partner most.
  • Saturn is fear and responsibility. The zodiac sign shows qualities that are very important to that person, who may try to express that sign in the extreme or run away from it. Saturn brings responsibilities to a couple in astrological compatibility.

See also which planets show compatibility.

Transposed Houses (Overlays)

Houses are important in synastry, first when you look at the basic tone of the natal charts; second, when you analyze the house overlays (see further down).

The houses are the twelve divisions of the horoscope wheel. Houses are sectors of human life. Planets are positioned in the houses by way of the zodiac signs. When a planet is in a house, the part of the individual represented by that planet is most readily expressed in the affairs of that house.

Basic Astrological House Meanings

The basic meanings of the houses are:

  • 1st house is the self, the physical body and new beginnings.
  • 2nd house is resources, income and movable possessions.
  • 3rd house is short (familiar) journeys, siblings, relatives, lower education and communication.
  • 4th house is home, family, father, parents and latter part of life.
  • 5th house is recreation, sex, love affairs, children and creativity.
  • 6th house is health, work, service and small animals.
  • 7th house is marriage, spouse, partnerships and open enemies.
  • 8th house is joint resources, debt, partner’s money, transformation and death.
  • 9th house is long journeys, higher education, religion, foreign countries, in-laws, publishing and the law.
  • 10th house is career, reputation, mother and public life.
  • 11th house is friends, hopes and dreams, community, stepchildren and business income.
  • 12th house is the unconscious, institutions, solitude, self-undoing, prisons, hospitals, sickness.

House Overlays

Below is a summary of meanings of planets in the partner’s houses, or house overlays.  Read more about the planets in houses in synastry.

  • The sun’s transposed house position shows an area of life you strongly identify with. Being preoccupied with affairs of that house makes you feel like your best self. Whichever house in your partner’s chart your sun is in, that is where you bring energy and vitality.
  • The moon’s transposed house position hows an area of life that you are very attached to. It is hard to be objective about affairs of that house, but it is also where your intuition works very well. Whichever house in your partner’s chart your moon is in, that’s a part of their life you are emotionally attuned to.
  • Mercury’s transposed house position shows the part of your life where your mind is most active. You are always giving and receiving information in the affairs of this house. Whichever house in your partner’s chart your Mercury is in, that is where you most easily share ideas with them.
  • Venus’ transposed house position shows the part of your life where you seek pleasure and comfort most. It is where you are most at ease and most capable of generosity and affection. Whichever house in your partner’s chart your Venus is in, that is where you bring love and a feeling of ease.
  • Mars’ transposed house position shows the part of your life where you are most aggressive. You are more likely to be physically active with the affairs of that house than others. It is where you try hard to get what you want. Whichever house in your partner’s chart your Mars is in, you exert your will there.
  • Jupiter’s transposed house position shows the part of your life where you are most optimistic. Good fortune and opportunities come to you most immediately in the affairs of that house than elsewhere. Whichever house in your partner’s chart your Jupiter is in, that is where you can be of great benefit to them.
  • Saturn’s transposed house position shows the part of your life that is quite important to you. Yet it is also that part of your life that seems most difficult to deal with. Your strongest fears are bound up with the affairs of that house, as is your sense of responsibility. Whichever house in your partner’s chart your Saturn is in, that is what you want them to take seriously.

Aspects in Synastry

Synastry aspects are the major angles that planets and key points in an astrology chart make to one another. Planetary aspects in a birth chart show how well-integrated the native is. Lack of aspects of mostly negative aspects reveal that the person is “at war with himself.” In relationships, planetary aspects between two people’s charts tell you how well-integrated they are as a couple (or whatever their relation may be).

A mixture of easy and hard aspects is often desirable to bring a balance. This is true for both individual horoscopes and compatibility.

To avoid over-complicating your reading, focus on the most important synastry aspects.

  • Conjunction - 0 degrees is a harmonious or easy aspect if the planets in the conjunction are benevolent like Jupiter or Venus. It is negative if the conjunction involves malefic or difficult planets like Saturn or Mars. Conjunctions in synastry can be a strong indication of compatibility.
  • Sextile - 60 degrees – a harmonious or easy aspect. Planets with this aspect cooperate with each other. Not as strong as a trine. It is the aspect associated with two zodiac signs of different elements but same gender (e.g. Aries and Gemini except for opposite signs like Aries and Libra). A sextile is a pleasant, harmonious aspect.
  • Square - 90 degrees – an inharmonious or difficult aspect. Planets with this aspect interfere with each other. It is the aspect associated with zodiac signs of the same modality but contrasting elements and gender (e.g. Aries and Cancer, Aries and Capricorn). A square can give problems to a relationship but it can also add a much-needed stimulation or balance.
  • Trine - 120 degrees – a harmonious or easy aspect. Planets with this aspect support and complement one another. It is the aspect associated with zodiac signs of the same element and different modality (e.g. Aries and Leo, Aries and Sagittarius). A trine creates harmony but too many trines can make a relationship very passive or extreme.
  • Opposition - 180 degrees – an inharmonious or difficult aspect. Planets with this aspect go in opposite directions. It is the aspect associated with opposite zodiac signs, which always share the same modality and gender, but different element (e.g. Aries and Libra). As you may well guess, opposition signifies strong attraction – or enmity.
  • Inconjunct and semi-sextile – 150 degrees and 30 degrees respectively – are minor negative aspects. They do not create enough tension to get as much attention as squared and oppositions do. But because the planets involved are often in highly incompatible signs, they still cause problems. It is often difficult to reconcile the differences between the planets with these aspects. For example, a sun in Leo and a sun in Capricorn have totally different ways of relating and acting in the world.

Horoscope Compatibility Tests:  What to Look for in Synastry

Below is a survey of key factors to look for in synastry.

  • Appearance and outward impressions as indicated by the ascendant and how it relates to the rest of each chart
  • Individual needs, preferences and values as shown in each birth chart
  • Compatibility between temperaments as shown by the zodiac signs and elements of both charts
  • Effects of  the partners on each other as shown by planets in one chart in the angles and houses of the other
  • Balance of easy and challenging influences, shown by harmonious and challenging aspects between the charts
  • Beginnings, changes and endings that can be gleaned from progressions and transits

For a step-by-step walkthrough of synastry, see how to do synastry with a free horoscope matching checklist.

Learn More on Compatibility

Horoscope compatibility is a fascinating part of astrology. Once you have become proficient in natal chart interpretation, you can attempt to study and compare charts. Use the above information as an aid to get started. For a much more in-depth look, it is strongly recommended that you read books on astrology.

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