Astrologers have found the charts of twins of very great interest.  Twins are often born very close to each other in time, and therefore often have the same or very close to the same energy imprint at the moment of their first breath—yet so many identical twins are very different in character, even though they look the same.

 One of my great interests in Astrology is genetic inheritance shown through the planets, signs and aspects.  For example, a member of one generation of a family; may be born with Neptune on an angle, one of their children may have a Pisces Ascendant, Sun or Moon,  and their grandchild may have an emphasised twelfth house, so we have a consistent flow of planet, sign and house throughout the generations.  Other members of  the same family are likely to have their Sun, Moon and/or ruler of an angle in aspect to Neptune, so you could say the family has a Neptune theme running through it.

 Whilst refining this system I thought I would check decanates (the division of the sign of the zodiac into three separate sections) and duads (the division of the sign of the zodiac into twelve 2°30’ sections).  I was both fascinated and astonished to find that the duad system clearly described, in detail, the genetic inheritance of a family line. 







The Duad System is a very ancient way of dividing the zodiac used by both western and vedic astrologers.

 Duads work on the premise that within each zodiac sign is a mini zodiac.

 Each sign is divided into 2.5 degree segments and each segment is a mini sign.

 For example:

The first 2.5 degrees of Aries is the Aries duad

2.5 –5.00 degrees is the Taurus duad

5.00 –7.5 degrees is the Gemini duad

.. and so on.

The last duad of Aries is the Pisces duad at 27.5—30 Aries.


The first 2.5 degrees of Taurus is the Taurus duad

2.5-5.00 degrees is the Gemini duad

5.0-0—7.5 degrees is the Cancer duad.

… and so on.

The last duad of Taurus from 27.5—30 degrees Taurus.is the Aries duad

 So each sign starts with its own duad and progresses in order of the zodiac until it finishes with the sign before it. (see table)

  A person will be very drawn to those who carry in their natal chart the same sign as their duad.  E.g. Someone who has the Sun in the Aquarian duad of Cancer will be very drawn to Aquarians and those with the Moon in Aquarius, even though this is not a sign that is normally considered compatible with Cancerians.  It is quite likely they will have an Aquarian parent, grandparent or child.

 I worked out a way to calculate duad charts by hand, and then Graham Dawson of Esoteric Technologies  was kind enough to incorporate the ability to calculate these charts into their Solar Fire Deluxe program.


 As each duad is a “mini sign” the 2½ degrees it covers can be converted into the 30 degrees of a normal zodiac sign and make a whole new duad chart.  It is relatively simple to calculate the duad zodiac degree by taking the start of the duad degree away from the degree of the planet and then converting that degree into the zodiac degree within that duad.

 For example:  Adam’s natal  Sun  is 8H23.  This is the Aquarius duad of Scorpio and that duad starts at 7.30° Scorpio


                                                            -           07.30

                                                            =            0.53

So Adam’s Sun duad is 0° 53’ into the Aquarius duad.

Using a calculator that calculates in units of 60, you can multiply  0° 53’ x 12 and this will give you 10°.36’ 

 Therefore Adam’s duad Sun is 10° 36’ of Aquarius.


To calculate the duad chart, highlight the natal chart on the first page of Solar Fire, then go to the “Chart” menu, click Vedic and then Vedic D12 Dwadashama.  Click OK.  The computer will ask you if you want to keep Western settings, click YES and you will have your duad chart.

 Whilst studying the charts of twins, both identical and non-identical, that were born very close together in time, I found that the duad chart for each twin clearly showed their differing natures and to an extent, the different experiences they have in life.

 This article will use the charts of identical twins, Adam and Bryan, to illustrate how the duad chart system works.

 As you can see, these two charts are nearly identical. Adam has an Ascendant of 24Capricorn21 and Bryan has an Ascendant of 24Capricorn57, so even the degree is the same for each person.

Likewise, Adam has a MC of 20Scorpio01 and Bryan has a MC of 20Scorpio30.

Adam has a Vertex of  28Leo32 and Bryan’s Vertex is 28Leo55.

It would be hard to get charts that are more identical, but these two twins have quite different lives.  For example,  one is the father of two children, the other is having difficulty starting a family.

Each would receive the same transits, progressions and directions at the same time, why would these produce different results?


Look what happens when I do their duad charts—


 Adam’s duad Ascendant is 22Libra12, indicating that he will be drawn to those with Libra rising and planets in Libra, particularly if they are around 22°.  He has no close aspect to this Ascendant, so no planets are influencing the Libra rising expression.  This Ascendant will give charm and a desire for beauty and harmony in his life.

The ruler of the Ascendant, Venus, is in Libra in the 12th house, suggesting that he would value his privacy and require quiet times to regenerate his energy.  Venus is trine the duad Aquarian Sun, increasing his charm and harmonious presentation to others.

His duad MC is 00Cancer07 indicating a desire to work with the public and/or nurture others.  Ceres is in close sextiles to this MC, suggesting that the nurturing tendency would be quite strong and perhaps gives an interest in cooking (Cancer) healthy foods (Ceres Virgo).  The duad MC is also sextile the North Node, giving an interest in working with others, perhaps in community  or family groups.  The ruler of the MC is the Moon in Sagittarius in the 2nd house conjunct Mercury, giving a need to make money (2nd house) through communication and/or trade (Mercury).  As Mercury is ruler of the 9th and 12th, this could perhaps involve publishing or overseas interests




Bryan also has a Libra Ascendant, Cancer MC and Leo Vertex in his duad chart, but the degrees are different and this difference brings into play an entirely different focus in life.

Bryan has the difficult, temperamental and stubborn duad Mars-Uranus conjunction in Taurus quincunx his duad Ascendant. It is also on the cusp of his duad 8th house, bringing pressure in the areas of joint finances. This configuration is square the North Node, further suggesting that there would be difficulties with financial affairs involving family, groups, and partnerships, particularly as Mars rules the 7th cusp and 2nd cusp.

Bryan has duad Saturn in Capricorn square his duad Libra Ascendant, bringing some restrictions into his ability to express himself harmoniously, and as Saturn is in his duad 3rd house, perhaps some problems in dealing with siblings.  Saturn is also quincunx the North Node suggesting flexibility and adjustment is needed in all situations connected to siblings and family.

On the plus side, Bryan has duad Jupiter trine duad Ascendant and conjunct duad 5th cusp.  This is helpful in self expression and beneficial for producing children. As it is conjunct duad South Node, it suggests that he has a karmic connection to his children.  Jupiter is ruler of his duad third house, so he would love his brother, despite the difficulties described by Saturn in the third conjunct 4th cusp.

Bryan will be more responsive to the 28-30° placements with transits etc., than his brother Adam, as these are brought into prominence by his duad Ascendant degree.



So you can see that even with a birth time difference of only two minutes, the duad charts describe two very different people, with Bryan having a duad chart  that shows  a great deal more pressure and tension than Adam’s.  Each duad chart emphasises different degrees and therefore different planetary placements.



These are shown when duad planets and angles connect to planets in the natal chart.  They put much greater emphasis on both the duad and the natal planet, so when transits, progressions and directions activate these positions there is often a strong reaction.  I will use Adam and his duad chart to illustrate:

You can see that the duad Pluto is conjunct natal Scorpio Sun at 8-9°.  This puts considerable emphasis on both the natal and duad placement.  This degree will be highly responsive to transits etc. Likewise, duad North Node is conjunct natal Vertex at 28-29 Leo, emphasing this degree for transits etc.  As this degree also resonates to Bryan’s duad chart, the transit triggers may affect him a little more than his brother Adam.

Adam’s duad MC is square natal Venus, so the natal Venus would resonate more to Adam when activated by transits, progression and directions



copyright (c)  Alice Portman/Alice McDermott 2007








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