Chart Rectification

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Grasping the exact moment - truly a difficult job

The reconstruction of a birth time, usually through timing important events in the person's life, and correlating them with hypothetical house cusps or axes. Many astrologers consider an exact birth time to be indispensable for an accurate natal chart interpretation, as determination of the rising sign, as well as locating planets and signs in houses, depend upon an accurate birth time. The accuracy of some predictive methods such as Primary Directions depends on the birth time being accurate to within a minute.

Unfortunately truly accurate official records of the time of birth are uncommon in western countries. Some birth registries record only the date of birth, and even a hospital record of the birth time might be rounded. Perhaps a person's mother remembers him being born "around 1:00" or only "late at night." (Accurate birth times seem more common in India, perhaps because of the greater acceptance of astrology there.)

In the past, determining accurate birth times was sufficiently difficult that astrologers pursued horary astrology as a means of answering practical questions. It is calibrated to the moment of the question being asked, which the astrologer could more easily determine once clocks came into widespread use.

Chart rectification "by hand" is a time-consuming exercise. There are now various computer programmes designed for chart rectification which makes the task easier and considerably less time-consuming. However, there is no objective external verification that a rectified time is, in fact accurate. Some astrologers argue that chart rectification based on concrete events is contradictory in spirit to esoteric and psychological astrology, which concentrate more on inner psychological processes rather than concrete events.

When the exact time of birth is unknown, the astrologer usually begins by inquiring about important events in an individual's life: for example, an important examination, wedding, birth of a child or the death of one of the parents. Then, with the help of various prognostic methods such as transits, solar arcs, and secondary progressions(it is advisable to use more than one method;) the astrologer looks to see whether these events occurred at the same time as important triggers on the axes, or hypothesized cusps of houses whose meanings correspond to particular events. These are the most individual factors in the horoscope because a small change in the time of birth causes them to move by several degrees. The ascendant and Medium Coeli (MC) move on average one degree of arc every four minutes.

Modern astrologers generally prefer the Placidus house system as being most sensitive to the timing of life events.

The following examples suggest how astrologers attempt chart rectification:

  • For each trigger which is thematically related, a hypothetical ascendant or MC is calculated, depending on which axis is triggered. Suppose the (non-rectified) ascendant is estimated to be in mid-Capricorn based upon an obviously rounded recorded birth time, like "around 2:00." On the native's wedding date, Saturn was at 16 degrees 15 minutes Cancer, i.e. near the corresponding descendant or cusp of the seventh house of marriage. The hypothetical ascendant would therefore be set to 16 degrees 15 minutes Capricorn. The underlying hypothesis is that the event and the trigger can be exactly timed, which may be true in some but not all cases.
  • A similar process is carried out using the MC as the basis. For example, perhaps the Capricorn rising person moved house (an Imum Coeli or fourth house matter) or received a major career promotion (a MC matter) when Jupiter was in mid-Libra.
  • The astrologer will continue this process with various life events. For example, the birth of a child should be a fifth house matter. After several iterations of placing the person's life events in appropriate houses and applying different predictive methods to them, the astrologer sets a birth time on the basis of which value appears to give the most accurate results.

Some astrologers will also try to rectify a chart on the basis of the native's physical appearance, but it becomes even more difficult to separate out the effects of genetics, where family members share physical traits regardless of their rising signs, than it does to time events. First house planets or planets aspecting the actual ascendant will also have an effect on the person's physical appearance.

See also



  • Regulus Astrology: A Rectification Manual: The American Presidency. 796 pages or ebook (pdf); 2007. ISBN: 978-0-9801856-0-7 Review online (Thomas Callanan, Skyscript 2008)
  • Dobyns,Zipporah Pottenger, et al., 2010. Progressions, Directions and Rectification, American Federation of Astrologers
  • Efrein, Laurie, 1987. How to Rectify a Birth Chart, The Aquarian Press