A birth chart is a map of exactly where the sun, moon, and every planet were positioned at the moment someone was born, based on their birth date, time, and location. Also called a natal chart, it's considered the foundation of a full astrological reading, since it goes far deeper than a sun sign alone.

A psychic or astrologer will often generate a client's birth chart ahead of time, then walk through it during the reading, pointing out key placements and explaining what each one reveals. Clients frequently keep a printed or saved copy of their chart afterward, since it's something many people like to reference and reread over time as they learn more about what each placement means.