In astrology rectification is the process of using astrological techniques and considerations in order to retrospectively determine when an event occurred, usually when that information is otherwise unknown or unavailable.
Rectification is most commonly used in order to determine a person’s birth time, either when no birth time is known, or when only an approximate time of birth is available.
The premise underlying birth chart rectification is that if a person’s birth chart is supposed to reflect both the nature of their life as well as events that will occur during the course of it, then it should be possible to infer what placements a person should have in their chart by working backwards from known events and circumstances in the person’s life.
In this way rectification is used either in order to determine information that would otherwise be completely unknown, or in order to fine-tune data that is already available, thus making the chart calculations more precise, in theory.
Rectification is usually viewed as a highly complicated and speculative process due to the number of factors involved in rectifying a chart. The fact that it is speculative and subject to error usually leads astrologers to view rectified charts as not very reliable for research purposes. Occasionally debates occur over which rectified chart is correct for certain celebrity nativities where the birth time is unknown.
An astrologer is said to “rectify” a chart, although the process itself is known as “rectification”.