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How do astrologers use a person's birth time and birth location in a natal chart?

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What's your sign? — astrology Zodiac wheel showing the 12 astrological constellations or signs from an illumination of the poem *Breviari d'Amour*, Catalan (Spain), late 14th century; in the collection of the British Library.

Astrologers use a person's exact birth time and location to construct a natal chart, which serves as a precise map of the heavens at the specific moment and place of an individual's birth.12

By inputting these details, astrologers determine the exact positions of the Sun, Moon, and planets relative to the local horizon. This data allows them to calculate the ascendant (the zodiac sign rising on the eastern horizon at the moment of birth) and the boundaries of the 12 houses. These houses act as the setting for various life aspects, while the planets' placements within them—and their geometric relationships, or aspects, to one another—are interpreted as a unique blueprint of a person's character and path.12

Essentially, the birth time and location are required to "mathematicize" the correspondence between the universe and the individual. By mapping these celestial coordinates, astrologers analyze how planetary influences, filtered through the zodiac signs and houses, supposedly shape an individual's life, personality, and personal growth.21