The sky turns one degree every four minutes or so, and on a forecast’s timeline, one degree of arc is roughly one year of life. So a four-minute error moves the calculated period by about a year, and a fifteen-minute error by about four years. That’s why we ask so carefully about your birth time and the dates of events in your life.
What exactly depends on the minutes
A birth chart is more than the positions of the planets. In four minutes the planets barely move: the Moon, the fastest of them, covers about two minutes of arc. What moves is something else: the starting point. The Earth rotates, and the whole grid that divides the chart into areas of life (work, money, home, relationships, health) turns with it.
The boundary of the first area of life is the point astrologers call the Ascendant, and the sign on it is your rising sign. At mid-latitudes, this boundary moves at roughly 0.2 to 1 degree per minute, depending on the part of the zodiac. Half an hour of difference in the birth time can carry it into the next sign entirely, and you get a different rising sign. On the surface, the reading will still hang together and even read beautifully. It will simply describe a life that isn’t yours.
Where “a degree equals a year” comes from
Forecasting techniques that go back about two thousand years use a simple device: the chart is, in a sense, rolled forward, and each degree of that movement stands for one year of a person’s life. It’s a convention of the tradition, not a law of physics, and different schools use slightly different rates.
From there, the arithmetic is simple. Four minutes of clock time give about one degree of shift. One degree on the timeline gives about a year. That’s the price of an error.
Why a hospital record doesn’t settle it
A recorded birth time is a good starting point, but not the final word. Times in records are rounded, usually to five or fifteen minutes, sometimes to half an hour, and they’re written down not at the moment of birth but when someone had the chance. So even when there’s a record, we check the time rather than take it on faith: we compare it with what has already happened in your life.
What this means for you
If you know your birth time exactly, we still check it, and then build the reading on it. If you know it roughly, it can be pinned down from events in your life: moves, marriage, the birth of children, big changes at work. If there’s no reference point at all, we don’t take the case; instead, we offer a personality reading without a birth time: it covers your character and strengths, but without tying them to areas of life or dated periods.
When the time is pinned down, the document also says how confident we are in the result.
The article “Why we start with your birth time” explains why we don’t read a chart until the time is established, and when the minute can’t be found.
Short answers to questions about birth time are on our FAQ page.