What Is a Birth Chart?

A birth chart (natal chart) is a map of the positions of planets and mathematical points in the sky at your birth moment — using date, time and place. It is an instant photograph of that sky.

A birth chart has four main layers:

Birth date, time and place (longitude + latitude) combine into universal time. Sidereal time is computed; planetary ecliptic longitudes are found from an ephemeris. The rising derives from the sign on the eastern horizon; houses spread from it.

Birth time is critical: without it, the rising and houses cannot be computed — only planetary signs (especially Sun and Moon) can be read.