Why birth time matters

When you book a reading, I ask for three things for each person: the date, the place and the time of birth. The date and place are usually easy. The time is the one parents most often hesitate over, so here's why it matters, and what happens if you don't know it.

Why minutes make a difference

A natal chart is a map of the sky from one place at one moment. As the Earth turns, the whole zodiac appears to rise over the eastern horizon once a day. The sign rising at the moment of birth is the Ascendant, or Rising sign, and it changes on average about every two hours.

The Ascendant sets the starting point for the chart's twelve houses, the areas of life each planet is read through. So when the time moves, the Ascendant and the houses move with it. A difference of even twenty minutes can shift a planet from one house to another, and near a sign boundary it can change the Rising sign altogether.

The date tells us where the planets were. The time tells us how they were arranged around one particular child.

Where to find the time in the UK

• Scotland: birth certificates record the time of birth.
• England and Wales: full birth certificates usually don't, except for twins and other multiple births. Look at hospital discharge notes, the red book (personal child health record), a baby book, or birth announcements.
• Your own memory, or a parent's: often surprisingly reliable for recent births, especially with something to anchor it, like a shift change or a phone call.

When you book, you'll be asked how certain the time is. "Approximately half past three" is far more useful than nothing, and I'll treat it accordingly.

What can still be read without a time

Quite a lot. Without a birth time I can still read the Sun and almost all the planets by sign, and the relationships between them. Those carry much of a chart's meaning. What can't be read reliably are the Ascendant, the Midheaven and the houses. The Moon moves quickly too, so on some days its sign is uncertain without a time; I'll always tell you when that's the case.

In a reading I'm always clear about which parts depend on the time, so nothing is built on guesswork.

A note on historical clocks

One more thing goes on behind the scenes. Every chart has to be calculated in the time zone and daylight-saving rules that actually applied at that place on that date, which aren't always today's. Britain, for example, stayed on summer time all year round from 1968 to 1971. For parents' charts and grandparents' charts especially, I check these rules for every birthplace rather than assume.