These questions are difficult to answer. But in general, it is believed among many meta-physicians that the moment of birth is predicated upon when the child takes its first breath. Before this moment, the child's nutrients are delivered exclusively through the mother. Taking ownership of one's life through a 'first breath' is like signing a contract. The astrological chart represented by that moment in time then acts a coded language for that soul contract. Since most doctors record the time of birth fairly close to this moment of 'first breath', the birth time listed on the birth certificate is typically close enough to allow for the derivation of an accurate birth chart.
But how exact does a birth time need to be in order to be useful for astrology? And can an astrology consultation still yield useful information without a birth time at all?
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What the Birth Time Tells Us
When a horoscope is cast, the point on that chart that represents the eastern horizon (far left of the chart) is known as the 'Ascendant' or AC. The sign in which this point falls is referred to as the 'Rising Sign'. For an individual, the rising sign is highly significant in terms of interpretation of the outward personality or mask that the person wears. This AC point within the rising sign is also essentially the starting point of the chart and the rest of the chart house system is set relative to this starting point.
While the speed of change of this AC varies based on things like latitude and time of year, on average, each sign ticks through the AC point approximately once every 2 hours. With 30 degrees of arc for each sign, that means that each degree moves through the AC point approximately once every 4 minutes. Considering that the house system of the chart is based on this starting point and that this starting point is in constant and somewhat rapid motion, it isn't difficult to see how important having an exact birth time can be for deriving an accurate horoscope.
For example, when I had my first astrological chart created over a decade ago I used the approximate birth time that my mother had told me which was 6:00pm (See Chart #1). However, when I saw my birth certificate a few years later I noticed that I was actually born at 5:44PM and NOT 6:00PM. If you compare Chart #1 (6:00PM) to Chart #2 (5:44PM) below, you can see that this 16 minute gap made a significant difference.
Chart #1 - 6:00PM (click to enlarge)
Chart #2 - 5:44PM (click to enlarge)
In both charts, the rising sign is Virgo and there is only a 3 degree difference in terms of the two AC points (25 degrees versus 22 degrees Virgo). However, my Sun/Moon opposition crosses over the horizon line (very significant zone) between one chart and the other. Also, planets like Pluto and Uranus fall in different houses between the two charts. These differences alter the interpretation of my chart with some significance and this is only a 16 minute discrepancy!
Chart #3 - 7:26AM (click to enlarge)
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Useful Information Regardless of Birth Time
Sometimes an accurate birth time just isn't available. In these case, there is still useful information present but there is just much less information. So a reading can still be conducted without a birth time but the depth of that reading, while still accurate, will be far less than one conducted with an accurate birth time. While the house positions of the planets vary widely throughout the day, the positions of the planets within the signs does not change much over a given day, in most cases.
For example, in all three charts above the Moon is in Virgo and it would have been in Virgo no matter what time I was born on that day in that place. Also, all of the other planets were in the same signs all day and the aspects between the planets did not change throughout the day either (i.e. the opposition between the Sun and the Moon). However note that the Moon travels approximately 12-14 degrees per day so on some days the Moon DOES change signs and without an accurate birth time it would be more difficult to assess the person's Moon sign if they were born on a day when the Moon changed signs. The same is true when other planets change signs on the day of a person's birth.
So even without an accurate birth time, the placement of the planets in certain signs and the aspects between the planets yield plenty of useful information with which to work. With this kind of information, a client can be informed of the energies that they have brought into this life. However, without a sense of where these planets fall into the house system of the chart, the clients soul intentions and lessons cannot be revealed with accuracy for the most part. Since most people who obtain astrological readings are interested in their life purpose and direction in this current life, an accurate birth time becomes very important.
For those who do not have access to their accurate birth time but who are interested in trying to derive their birth time, there is a process known as chart rectification. This process involves using a diary of events and experiences from a person's past to piece together a map of their journey which can then be used to attempt to create a chart and its derived birth time. There are several astrological practitioners who specialize in this process but the results need to be taken with a grain of salt.
In general, it is more valuable to have an accurate birth time for a complete astrological reading but that does not mean that useful information cannot be derived from a chart of a person without an accurate birth time.
