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How do planetary aspects influence an astrological 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.

In astrology, planetary aspects are geometric interrelationships between celestial bodies that influence their strength and significance within an astrological chart. These aspects, along with the planets' positions in houses and zodiacal signs, are fundamental to the practice of reading a horoscope.1

Planets exert mutual influence by occupying each other's houses and through specific angular configurations. These aspects are generally categorized by their perceived nature:1

Harmonious Aspects: Trine (to the 5th or 9th house) and sextile (to the 3rd or 11th house) are typically considered good or favorable.1
Challenging Aspects: Opposition (to the 7th house) and quartile, or square (to the 4th or 10th house), are generally regarded as difficult or unfavorable.1

By examining these intricate geometric connections, astrologers interpret how planets of varying computed strengths interact with one another and the places in the chart to derive predictions. While these methods are used to map out personality traits or life events, it is important to recognize that astrology is a system of divination rather than an empirical science, and its claims regarding the determination of human life are not supported by scientific evidence.12