People who do not know the time of their birth can be possible as there some of them who basically does not know their origin such as individuals who have been under adoptions. There are astrologers who perform what is called “chart rectification” of the birth time to forecast ones horoscope. Take note that rectification is only use to determine time of birth and it cannot determine the date of birth. It may sound odd or funny but yes, birth chart rectification can only determine time of birth and not date of birth. 

How does birth chart rectification work? The most common and used methods or birth chart rectification are based on advance techniques that utilize transiting solar arc and/or progressed planets passing over what are called “chart angles” and that are determined by time of birth. These are most noted for often resulting in “real”, physical, time and space events happening in one’s life. Astrologers basically work backwards through astrology’s predictive techniques. It is the chart that over the course of many years which appears to be working in your life. Though it gives no assurance for its credibility but it is still being relied upon for the future work.

A list of 15 significant live events will be asked by your astrologer to perform rectification. These events are spread out over the course of the person’s entire life time. It might include marriage, divorce, death of loved ones, birth of a child, other significant relationships, getting fired, going to jail, travels, achievements, etc. It is advisable that you provide events that happened with a 6 month year period as these muddy up the waters of the rectification process. A brief description is needed and not long detailed confessions.

If it is possible for you to check old records to find exact dates, then do so. Take note that dates vaguer than a year and a month are not so useful.

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Source : BirthChart.com.au