The most accurate way to look at astrological compatibility between two people is not just their Sun signs or even their Venus signs, though both are important.
The best way to assess relationship compatibility with astrology is to look at the two people’s birth charts together. This way of stacking the charts together is called synastry.
Another technique called a composite chart can also be used to assess a relationship with astrology, and I will go over the distinction between a synastry chart and a composite chart.
I will give some examples using the charts of The Beatles and then show you how to use an interactive synastry tool to analyze the relationship between Taylor Swift and Joe Alwyn.
Table of Contents
Compatibility Chart Data Basics
An astrological chart gives you a snapshot of the position of the Sun, the Moon, and the planets at the moment a person was born. If you have not yet seen what a basic astrological chart for one person looks like by itself, please do so with the tool below.
The pieces of information you need to construct an accurate astrological chart for anyone are the date of birth, time of birth, and city of birth. If you are going to make a synastry chart that assesses relationship compatibility for two people, you need to do your best to get this information for each of the two people.
My article on Katy Perry explains why time of birth and city of birth are especially necessary to know the Moon sign and Rising sign. As elaborated in my article 7 Most Important Aspects of a Natal Chart, the Rising sign is one of four angles that shape the chart. Knowing an accurate birth time is necessary to know any of the angles.
Most astrology software will not let you proceed in constructing a chart without putting in something for the time of birth and city of birth.
If you know the date of birth only and are not able to find time of birth or city of birth, put in 12:00 p.m. for the time and the capital city of the state or country the person was born in for the city for a rough estimate.
You do need to be aware that estimating the time and/or city will not give you an accurate Rising sign. The Rising sign moves through all 12 signs over the course of a 24-hour day, so you have a 1 in 12 chance of guessing right.
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The Moon spends a little over two days in each of the 12 signs during its cycle from one New Moon to the next. If you must estimate a birth time, and the Moon changes sign on the day in question, you have a 1 in 2 chance of guessing the right Moon sign.
You would be guessing between two adjacent signs, like Aries and Taurus, rather than between two signs that are far apart from each other like Aries and Libra.
Where To Get Data
If the person whose chart you want to look at is already famous, that makes it easy, as there are many websites that provide astrological data on celebrities. These include Astro-Databank and Astro-Charts.
If the person whose chart you want to look at is not a celebrity, the best way to get their birth information is to ask them directly. If they don’t know, they may need to ask their parents or look up their birth certificate or birth announcement.
If your relationship with that person is not strong enough that you feel that you could ask them, then that might tell you something about the relationship.
It is very common for people to do endless Tarot readings asking how some other person feels about them, but if you have to ask the cards instead of asking that person directly, then that pretty much answers your question.
As opposed to a Tarot reading, however, astrology can get you some basic mathematical information independent of anyone’s feelings toward anyone. This is especially relevant to the slower-moving cycles of the outer planets like Uranus, Neptune, and Pluto.
For instance, suppose you were born in the late 1980s and have Venus in Libra square Neptune in Capricorn in your natal chart. Most people born in the late 1980s and 1990s have Neptune in Capricorn, so, if you have a partner the same age you are, your Venus will be square their Neptune too.
They will therefore strongly interact with the tendency your Venus-Neptune square gives you to idealize people and have poor boundaries.
You could get tired of this and decide to date someone ten years older. However, you will soon discover that most people born in the 1970s and early 1980s have Pluto in Libra, so everyone ten years older than you has Pluto conjunct your Venus.
A Venus-Pluto conjunction in synastry is an intense connection. At best, it can be transformative, but, at worst, there can be serious issues with power and control. At baseline, important things might tend to be unspoken.
Is trading the boundary issues of a Venus-Neptune square in synastry for the power issues of a Venus-Pluto conjunction in synastry worth it? It’s hard to say, but, with astrology, you can at least know which you are getting into.
You don’t even need to know a prospective partner’s month of birth to see larger patterns like that. If you tend to have specific relationship issues with people of a particular generation but not with everyone, patterns like this would be worth looking at.
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Synastry stacks two astrological charts together, as shown in the example of John Lennon and Paul McCartney, the two main songwriters of The Beatles, below.
The same technique can be used for any type of relationship whether it is romance, friendship, business, or family. John’s chart is in the inner ring, and Paul’s chart is arranged around it in the outer ring.
The charts for the examples of The Beatles were made in a computer program called Solar Fire. The red and blue lines in the center of the synastry chart show aspects between John’s chart and Paul’s chart.
As discussed in 7 Most Important Aspects of a Natal Chart, Solar Fire colors the hard or challenging aspects red and the soft or harmonious aspects in blue, though not all astrology software follows this color coding scheme.
One type of hard aspect is called a square, and it is between points that are 90 degrees, or three signs apart – from Aries to Cancer, for instance. The other type of hard aspect is called an opposition, and it is between points that are 180 degrees apart, or across the circle from each other – from Aries to Libra, for instance.
Harmonious aspects are trines, 120 degrees or four signs apart, and sextiles, 60 degrees or two signs apart.
Conjunctions are planets or other points that are within just a few degrees from each other. For any aspect, a few degrees of rounding is usually allowed.
When looking at synastry charts of two people who are close in age, it is important to be aware that they will typically have the outer planets like Uranus, Neptune, and Pluto in the same positions. In this example, John was born in October 1940, and Paul was born in June 1942, so they are less than two years apart in age.
They both have Pluto in the early degrees of Leo and Neptune in the late degrees of Virgo, though John has Saturn and Uranus in Taurus and Paul has Saturn and Uranus in Gemini.
Point being, if you use the synastry tool further down this page to buy a synastry report for yourself and a partner who is close in age to you, do not be surprised if the report notes that your Pluto is conjunct your partner’s Pluto.
That just means you grew up in the same generation as your partner, which you already know. Be more interested in connections like one person’s Sun conjunct the other person’s Moon or Mars.
7 Most Important Aspects of a Natal Chart breaks down the distinction between outer planets and inner planets further. In general, what you should look at first in a synastry comparison is the aspects between the Sun, the Moon, and the inner planets in the two charts. On this level, John’s Sun in Libra is closely sextile Paul’s Moon in Leo and trine Paul’s Mercury in Gemini. These are good harmonious connections.
Aspects between one person’s Sun, Moon, or inner planets and the other person’s outer planets can be important. In this example, Paul’s Venus in Taurus, an inner planet, is conjunct John’s Jupiter, Saturn, and Uranus, all outer planets, in Taurus.
Venus and Jupiter together can produce luck, and Venus and Uranus together can produce surprises, and The Beatles did get a lot of lucky breaks that led to their surprising success. Saturn in the mix gave John and Paul enough commitment and discipline to take advantage of the opportunities they received.
However, Paul’s Moon in Leo is square John’s Jupiter, Saturn, and Uranus in Taurus, suggesting that the relationship with John was sometimes emotionally difficult for Paul.
John has Pluto in Leo opposite his Moon in Aquarius; anyone close to John’s age, including the rest of The Beatles, has Pluto in Leo opposite John’s Moon in Aquarius, so John may have had difficulty getting along with his peers in general.
Meanwhile, Paul’s Saturn and Uranus in Gemini are trine John’s Moon in Aquarius. Harmonious aspects involving Saturn can provide stability and structure, so John probably found Paul a stabilizing force. Harmonious aspects involving Uranus can provide freedom and creativity without being too disruptive, and John likely found that in Paul as well.
Finally, John’s Venus in Virgo is conjunct Paul’s North Node in Virgo, suggesting that the relationship was destiny for both of them.
While the synastry capabilities on both Astro.com and Astro-Charts are limited to two charts together, Solar Fire will let you stack up to five charts together. You can therefore look at a synastry chart for all four of The Beatles as shown below. Solar Fire also comes pre-loaded with some celebrity data, and oddly this included only three of the four Beatles – I had to add George Harrison in from Astro-Databank myself.
All four men have Pluto in Leo, which is to be expected given that they are all close in age. George and Ringo Starr provide additional emphasis in the sign of Leo, which makes sense for a group of artistic performers.
Paul and Ringo both have Mars-Pluto conjunctions in Leo, so that is a lot of creative energy that they needed an outlet for!
Synastry Versus Composite Chart
A more advanced technique for relationship astrology is composite charts. Instead of two charts stacked together that can be clearly differentiated from each other, a composite chart makes one chart by taking an average of the positions of each celestial body in each chart.
For example, in the synastry chart for John Lennon and Paul McCartney above, Paul has the Sun in Gemini, and John has the Sun in Libra. In the composite chart for John and Paul below, the Sun is in Leo, the sign halfway between Gemini and Libra.
In the synastry chart, Paul has the Moon in Leo, and John has the Moon in Aquarius, so the Moon in the composite chart is in Scorpio, halfway between Leo and Aquarius. This is repeated for every single significant point in the individual charts.
Synastry is easier for beginners to understand than composite charts, but you should know what composite charts are in case you come across other websites talking about them.
The distinction between synastry and composite charts can also be helpful in looking at a relationship in different ways. In synastry, each person remains a separate individual.
Composite charts, however, may be useful for assessing situations where the twosome is greater than the sum of its parts, or where the relationship brings out something really out of character in one or both of the people involved.
In John and Paul’s composite chart, Venus in Cancer close to the ascendant makes a lot of sense for the wholesome, clean-cut image The Beatles portrayed in the early days of Beatlemania.
John, overall an edgy guy, would be unlikely to come off that wholesome by himself, so this would be a situation of the relationship bringing out something out of character for at least one of the people involved.
Synastry Example: Taylor Swift and Joe Alwyn
Now I will show how I did the case study described in my article What Astrology Has To Say About Taylor Swift and Joe Alwyn? You will get to follow along with the synastry widget included here.
The first step is to acquire the birth data. I got Taylor Swift’s birth data from Astro-Databank. Astro-Databank notes that there are two different birth times floating around on the Internet for Taylor but makes a case for December 13, 1989 at 5:17 a.m. in Reading, Pennsylvania.
Joe Alwyn was not listed in Astro-Databank, so I found him on Astrotheme. Astrotheme admits that Joe’s time of birth is unknown but says he was born on February 21, 1991, in London, England, United Kingdom. Astro-Charts has the same information and does not have a time of birth for him either.
Now we will put that data into the form below. Because we have a known birth time for Taylor and none for Joe, we need to put Taylor’s data in the top slot of the form.
Synastry charts set up the angles based on the first person you enter. If you know the accurate birth time for one person and not the other in a synastry chart, put the person whose birth time you know in first so that the synastry chart will be set up with their known angles.
Solar Fire then puts the first person on the inner ring, while the tool below made by Astro-Charts puts the first person on the outer ring.
We will then put in a 12:00 p.m. birth time for Joe knowing that it is just an estimate.
With a 12:00 p.m. estimated birth time, Joe’s Moon comes up near the end of the sign of Taurus. However, it is so close to the end of the sign of Taurus that he could have the Moon in Gemini if he were born late in the day, so be aware of that ambiguity, and do not get attached to the idea of Joe having the Moon in Taurus.
You must also disregard entirely all four angles generated for Joe – Ascendant, MC, Descendant, and IC – as we do not know his birth time.
This tool, made by Astro-Charts, color-codes the aspects between charts differently from Solar Fire and Astro.com.
Of the hard aspects, squares are coded as red, and oppositions are coded as blue. Of the harmonious aspects, sextiles are coded as purple, and trines are coded as green.
The yellow lines refer to the quincunx or inconjunct, which is a type of connection that can best be described as awkward. The grey lines refer to minor aspects used by advanced astrologers.
One of the two big green trines in this synastry is between Joe’s Venus in Pisces and Taylor’s Mars-Ascendant conjunction in Scorpio. The other is between Joe’s Sun in Pisces and Taylor’s Moon in Cancer.
As I noted in my original analysis, this emphasis on water signs in the synastry between Joe and Taylor shows that the relationship between Joe and Taylor brings out the more sensitive parts of Taylor that may not be as obvious in her fiery Sagittarius Sun persona.
As for the big red squares in the synastry, Taylor and Joe are close enough in age that they both have Pluto in Scorpio in about the same position. Taylor has Pluto in Scorpio square the North Node in Aquarius in her own chart, and Joe has Pluto in Scorpio square Mercury in Aquarius in his own chart.
These configurations therefore overlap in synastry so that Taylor’s Pluto in Scorpio is square both her own North Node and Joe’s Mercury, and Joe’s Pluto in Scorpio is square both his own Mercury and Taylor’s North Node.
However, both Joe and Taylor would have this issue with anyone who was close to their own age.
Finally, let’s look at Venus sign compatibility for Taylor and Joe. As noted, Joe has Venus in Pisces trine Taylor’s Mars-Ascendant conjunction in Scorpio.
However, Joe has Saturn in Aquarius closely conjunct Taylor’s Venus in Aquarius.
While connections between Venus and Saturn in synastry are sometimes associated with restrictions in love, they can bring commitment and stability to a relationship that has other more favorable indicators as this one does, as was also the case for John Lennon and Paul McCartney.
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