The birth chart

Imagine standing where you were born, at the minute you were born, and photographing the whole sky, including the half below the horizon. Flatten that sky into a circle and you have a birth chart. The outer ring holds the twelve zodiac signs, the planets sit where they were along that ring, and lines across the middle mark the angles between them.

Three pieces of information make the chart: date, time and place. The date fixes where the planets were. The time and place fix how the sky was turned relative to the horizon, which decides your rising sign and your houses. That is why an unknown birth time still gives you planets in signs, but not houses or an Ascendant.

Clock time is trickier than it looks. Countries change time zones and daylight-saving rules; Korea, for example, used UTC+8:30 in the 1950s and daylight saving in 1987 and 1988. We convert your local birth time with the historical time-zone database so the chart reflects the sky you were actually born under.