Astrological synastry—a case study on relationships and compatibility

An Examination of Two Peas in a Pod

(Previously posted on the blog,

Siblings– two peas in a pod, right? Even though they do come from the same pod and they’re nurtured in the same garden, often the differences between them are like night and day. And conversely, the similarities can be so exact that it’s hard to tell where one ends and one begins.

Sisters and brothers are a unique group in that they share at least one common parent and almost always a common background. It amazes me sometimes how differently they view their upbringings. What they’re really expressing is how they view the world and what they expect from it.

How can these two peas  from the same garden view the world so differently?

We astrologers are fascinated by this question and have an entire branch devoted to the study of it. We call it synastry – the study of relationships and compatibility by comparing the astrological charts of the individuals involved. We look at the similarities, differences, and placement of the planets as well as the relationships these planets make to each other’s charts.

Margaret and Marion, the Sister Project sisters, are two years apart. We’ll use synastry to take an astrological look at their relationship. Synastry is a complex study and astrologers approach it in sections. First, we look at the overview– each individual and how they relate to themselves, their environment and each other as a whole– for our first impressions.

Marion, a redhead, is an Aries. Aries is ruled by the planet Mars, named after the god of war. Aries rules how we take action, how we get things done. Aries, the sign that rules iron (and the color red) is rarely interested in stopping to gather information before it acts; to an Aries– action is the end that justifies all else.

There are ten planets and twelve areas of life in a chart. Marion’s planets are placed all through her chart, indicating that not only does she like to take action; she likes to take action on many different interests at the same time. She’s a very social person with strong maternal feelings who easily empathizes with others. Her views of environment and family are very similar and expansive– a we are the world  perspective.

Two of the ten planets (20% of her energy) are located in her third house– the house of siblings, environment and communication. Both of these planets are very expansive, intense, persuasive and powerful and one of them is the most intense of all of the planets. When dealing with this Aires, its probably easier to do it her way at the outset– with her deep level of intuition, she’s not only often right; she’ll find a way to talk you into it, anyway. So, when she’s dealing with her older sister, Margaret, she can feel she knows best and be very insistent in telling Margaret what to do and how to do it.

How does Margaret deal with and feel about that? Well, Margaret’s no slouch, herself. She’s a Gemini, ruled by the planet Mercury. Mercury rules communication, environment, siblings and the third house. She lives to gather information and because of the very focused and specialized placement of her chart planets (along with her very deep level of intuition), she can use her skills and gifts to score winning points in any discussion. With her moon in the conciliatory sign Libra, however, sometimes she’d rather have peace than win. Because of this, Marion (and others) can underestimate her and can be very surprised when she decides to stick to her guns.

Margaret is very social, too, but her view of family and friends differs from that of her sister’s. She has the most intense sign on the cusp (doorway) of her third house and the least emotional, most sensible planet in that house. Becoming a part of her inner circle takes time. Time spent, the quality of that time and her experiences with a person are how she determines the value of her relationships.

Because of her third house signs and planets, she’s often cast in a very familiar role for her– that of the caretaker, the older  sister in many of her relationships, including her sibling relationship with Marion. Both sisters value loyalty very highly. They have a karmic relationship and love each other very much.

Next, we’ll take a closer look at the planets in each sister’s third house and how they relate to each other as they emphasize similarities and differences.


In Part 1 of the astrological chart comparison (synastry) of Margaret and Marion, the Sister Project sisters, we looked at the overview of each individual and how they relate to themselves, their environment and each other as a whole. In Part 2, we’ll take a look at the planets in each sister’s third house and observe how they relate to themselves and each other as they emphasize their similarities and differences.

When I look at the planets in each sister’s third house, I see from the planet’s placement and from the aspects these planets make to other planets in each other’s charts that their sibling relationship is a karmic one and their bond is very strong.

Margaret has the planet Saturn, the least emotional and most sensible planet, in Scorpio, the most intense sign, in her third house. She was born knowing that she has to make sure that her sister (and those in her environment) is safe and taken care of and that boundaries are established and maintained. Because the third house also governs communication and information, she often feels compelled to gather knowledge and share it with those in her environment. Since Saturn is the planet that governs the planet Earth, everyone on this planet is in her environment. It makes sense that she’s a writer and it makes sense that she would want to co-create a way for sisters to share their personal third house– sibling– experiences with each other and the world. (People with planets in the third house search for meaning and seek connection.)

The relationships the planets make to each other are called aspects. Margaret’s Saturn in Scorpio aspects Marion’s Moon in Pisces (The moon rules intuition, emotional foundation, family) and she often just knows  what Marion is thinking and how she’s feeling without having to speak to her. Although this ability of Margaret’s might not have always been appreciated when they were growing up, I’m sure that Marion is happy about it now. Both the Moon in Pisces and Saturn in Scorpio are infinity  placements– they strongly indicate many deep past life connections between the sisters.

Marion has two planets in her third house– expansive, lucky Jupiter and intense, passionate Pluto– both in the very social, dynamic sign of Leo. Leo is governed by the Sun and the Sun, as we all know, gives light and life to our planet. Leo governs the heart; the third house governs our arms, which we cover with sleeves, so its no surprise when I say Marion wears her heart on her sleeve. Marion’s environment is serendipitous. Unusual, intense, often wonderful and lucky things happen for (and to) her. She makes intense, heartfelt connections immediately– with almost everyone.

With Jupiter in the third house, boundaries are rarely an issue and that includes all of the man-made boundaries, as well. Country’s borders, people’s races, society’s classes don’t mean a whole lot to her– everyone is a potential sibling. She leads with her heart and she uses that, along with her very intuitive Moon in Pisces and powerfully intense Pluto in Leo, to guide her. Being an in the world, of the world  person, she sees the glass as half full, even when its empty!

Sometimes, Marion’s open-armed view of life can be unsettling to Margaret. Margaret learned early about the need for judicious caution as she dealt with the world. Marion’s learning and acceptance of judicious caution came much later in her life. This is not to say that Marion is clueless or immature when it comes to dealing with her world– with Pluto in Leo also in her third house, and her ruling planet Mars in the very mature and wise sign of Capricorn, she’s quite capable of handling whatever comes her way. It’s just that with Jupiter in her third house, she’s very protected by the gods and hasn’t always had to use the kind of caution that the rest of us do.

Marion’s Jupiter and Pluto in Leo aspect her sister’s Sun in Gemini and Moon and Neptune in Libra. More proof that they really don’t need phones or e-mail in order to communicate with each other. And more proof that they’ve known each other for many lifetimes. What Marion teaches Margaret is to trust the value and power of spontaneity and what Margaret teaches Marion is the need for balance and clear communication.

They are fiercely loyal to and protective of each other and to those whom they welcome into their world. Whenever Saturn and/or Pluto are found in the third house, you’ll find that that person has an interesting combination of loyalty, stubbornness and commitment.

The third house also rules mirrors and what they reflect back to us. As time goes on and they continue to grow as individuals, third house residents and sisters, Margaret is finding more expansive aspects of herself as she connects with the reflections that her sister’s life mirror shows her. Marion is benefiting as well, from the values of containment and focus that Margaret’s life mirror is showing her. Through their experiences, they’ve arrived at a wonderful stage where they can see how their planetary placements and aspects are helping them to know just how much their similarities and differences complement each other.

In Part 3, we’ll take a look at their composite chart. A composite chart is created from the merged planets in each sister’s astrological chart and it shows us the purpose for and the power of their relationship.


In the first part of this astrological chart comparison (synastry) of Margaret and Marion, we looked at each of them as an individual and how they relate to their environment. In Part 2, we looked at how they relate to themselves, each other and their world.

Now, we’ll look at their composite chart. A composite chart is created from the merged planets (energies) in each sister’s astrological chart. It’s been said that in each relationship, there are three people present you, the other person and the relationship itself. The composite chart tells us the story of the third character the relationship as it shows us the purpose for the relationship and the power of it.

Through studying and interpreting the signs and house placements of the ascendant (how the relationship is viewed by the world and how it expresses itself), the sun (the identity and power source of the relationship), the moon (the inner motivating forces of the relationship) and the sign on the third house cusp (the siblings area of the chart), we can tell a lot about their relationship.

When the two Roach sisters combine their energies on any project, they and the results of their efforts show up as dynamic, expressive, playful and transformational.

The ascendant of the composite chart is the dynamic, attention attracting, heart-centered sign of Leo (think grand! expressive! fun!). Because they want everyone to participate in and benefit from their production, their combined vision is grand and almost always involves a presentation of some kind. Together, they seem to channel  the energy of the classic 1930’s movies of Judy Garland and Mickey Rooney they produce inspiring projects that they’ve written, costumed and built the sets for.

The sign on the ascendant, Leo, is governed by the sun and the sun in the composite chart is located in the 10th house, the area of high visibility, success and societal concerns, and is in the very earthy, detail oriented, patient sign of Taurus. (Margaret and Marion also have their suns in the 10th house.) Taurus knows how to get things done with a great sense of beauty, grace and value. Whenever a chart has the sun in the 10th house, the public is always aware of what the person (in this case, the individual and the combined energies of Margaret and Marion) is up to.

Margaret’s sun is in the sign of Gemini and Marion’s is in the sign of Aires great for ideas and energy, but not so much for patience or for dawdling with details. When they combine their efforts to manifest their vision, they often have to adjust their naturally speedy timetable to a more measured pace. After all, you can only move as fast as the slowest member of the troupe, and Taurus, the relationship’s sun sign, is not known for speed.

This can be frustrating for the sisters, but the delay often proves beneficial because they discover something that they’d have missed if they hadn’t been slowed by circumstances. And by now, they’ve learned that when they put their heads together, their will be success with all of those 10th house suns what else could there be!

The moon the planet of inner motivating forces, nurturing and the public is in the lucky, expansive, spiritual sign of Sagittarius, and is located in the dramatic 5th house, the area of teaching, creative self-expression, life’s stage , the heart and it’s governed by our solar system’s life-giving source the sun.

The strength of their motivations is almost like a calling . When they agree to work or play together, there’s often a feeling that they’re being directed or assisted by the Universe. All sorts of serendipitous happenings occur and they, along with the rest of us, experience an essential type of soul growth and a profound sense of connectedness to life and to each other. With Margaret’s balance oriented Libra moon and Marion’s fluid Pisces moon, they simply have to keep in mind trust, openness, flexibility and play everything will always work out just fine.

The 3rd house is the area of siblings, communication and the environment. Their relationship chart has the sign Virgo on its cusp. Virgo is governed by the planet Mercury, the planet of orderly systems and projects as well as communication, the environment and siblings! Mercury is also located in the 10th house and is very close to the 11th house, the area of humanitarians, hopes, wishes and friends.

There are three recurring themes in the relationship chart of the Roach sisters. The first is dynamic expression benefiting the masses because the sun, which is in the 10th house, governs the ascendant’s sign Leo and therefore rules the relationship. The second is communication and community because of the planet Mercury, which governs the areas of value and communication in their synastry chart and is also in the 10th house. The third is establishing kinship through interaction with the public because the 10th house has two prominent planets in it.

These two sisters are beautiful ancient souls who have lived many lifetimes in each other’s company. Though their individual approach to life is different, they’re both on the same page when it comes to shared goals and values. Using the combined energies of the heart and the mind, they delight in discovering ways to make life work better just as much as they delight in generously sharing that knowledge with us.