Specific areas in the birth chart show how people react in a relationship. This is not limited to emotional relationships, and it also encompasses friendship, the professional field, or the relationship between parents and children. Suppose you are thinking of opening a business with another person, for example. In that case, synastry helps in the study of the personality traits of both, which will result in a greater harmony of the relationship.
The starting point for synastry is the analysis of the birth chart. When trying to study a particular type of relationship, it is necessary to analyze both letters. Otherwise, the report is limited to the characteristics of one part of the equation, making it impossible to analyze the interaction between the two personalities.
On the other hand, the complete analysis of synastry implies knowledge of the Ascendant and the Midheaven. When the date of birth is unknown or uncertain, it is impossible to analyze these critical data to characterize the astrological personality, and the synastry report remains incomplete. Similarly, when there is uncertainty about the time of birth, there may also be doubts about the moon sign, if the Moon has changed the signs.