A birth chart or Earthlines map cast for a twin is virtually the same. The Rising Sign (Ascendant) changes approximately one degree every four minutes. A chart for twins born ten minutes apart will have only a couple degrees difference, so unless the rising sign was changing signs while you were being born, odds are good everything will track the same. However, one set of twins had a natal planet on the second house side of a cusp, and the other had it slip into the third house, a very tiny distance. The second house twin was very focused on making money (a second house trait), and the third house twin was an education junkie, taking every class that came along (third house). The other way that you can see a difference is to look at the Sabian Symbols for the degree of the ascendant to find symbolic difference (see Marc Edmond Jones, Dane Rudhyar or Lynda Hill books on Sabian Symbols)
One philosophy is that one twin takes after the father and the other the mother. So while their charts are nearly the same, the way they express them is different. One example is non-identical female twins with a natal moon in the fifth house of children, romance and creativity. One woman was very pretty and had a full life of marriage and children. The other twin was not attractive and did not manifest relationships easily, but had a great sense of compassion she used as a nurse to children. Although their lives looked very different on the exterior, both were working with fifth house issues. The core issue of the fifth house is opening your heart; there are just different ways to do it. An old African tale says that the twin to come out second is the one with wisdom because they had the patience to wait.
The benefit of doing each person’s chart individually as an adult is that although the core lesson may very well be the same, life experiences and environmental factors are likely to be different.
The other question that comes up is Caesarian births where both have the same birth time. A study done long ago by France’s Gauqualin looked at planetary placements at the angles of the chart (for example, the ascendant) to see if great athletes, surgeons, generals, writer’s, etc. had a statistical preponderance when a specific natal planet was at the angle of a chart. So athletes had warrior Mars on an angle of the chart. Caesarian births threw the data research off, so they had to pull them out because only natural births tracked with this research. This study was done before induced births came into being, so there is no data when a birth time is chosen based upon the doctor’s schedule.
On the Earthlines (AstroCartoGraphy) Maps, a ten minute birth time will show only a tiny difference in the power lines drawn on the chart (unless you were born near a solstice at a high latitude like Alaska). It is actually fine to do one map for both twins born close to each other; however, life experiences as one gets older and wiser can flavor the interpretation of the maps for each individual. For example, a Pluto line is ultimately about stepping into your power. Where one twin may get lessons in using power in the world (like a corporate manager), the other may go through death experiences to learn to let go (like a hospice worker).
On average, the Ascendant (AKA Rising Sign) changes about one degree every four minutes. The Ascendant represents the constellation on the eastern horizon when born, and it tells how you project yourself into the world. It has to do with self-esteem, assertiveness, athletics, etc. So, twins born 5 minutes apart are likely to have the exact same chart with only a one degree difference in the set up of the chart.
People often ask, especially in non-identical twins, why they are so different when they have the same chart. Different life experiences, even as small as the order of birth, make for some of the differences. On another level, the differences may not be as large as they seem to be on the surface. For example, one set of non-identical twins had a fifth house emphasis. The fifth house represents children, romance, and creativity. One of the twins put a lot of effort into romance and the other put effort into working with children. Their behaviors looked very different on the surface, but both were actually gaining different experiences from the same area of their chart.
Another example is of identical twins born 20 minutes apart. This small time difference put a planet in the second house of money for one twin, and barely in the third house of education for the other twin. The twin with the planet in the money house was totally focused upon the material world while the other was focused on education. So a minute difference in birth time can make a difference.
The other thing that can be done is to look at Sabian Symbols. These are esoteric symbols from a psychic in the 1920’s, where she looked at each degree of the zodiac and psychically came up with an image for the degree. So in the case of twins born five minutes apart, there was a one degree difference on the important action zone angles of the chart. You can look up the symbols for the different degrees and find information about the differences between the twins.
An old African tale suggests that the second natural born twin out of the womb is the wise one because they had the patience to wait. I have not seen any significant research on Caesarian or induced births to provide insight into twins born at the same time due to the C Section birth.
A French astrologer researched charts of famous athletes, doctors, generals, writers, etc. and found that four power zones in the chart called angles (the Ascendant, or Rising Sign, is an angle) showed that planets in these zones produced a statistical higher preponderance of people who excelled in professions associated with the planets near the angles. They found that this was true for natural childbirths, and that it did not work for Caesarian births (this was done before induced births, so new research needs to take place).
In regards to the relocation astrology maps, the maps of twins born at almost the same time are almost exactly the same.