The oldest astrological traditions placed the Sun at the center of meaning long before Copernicus placed it at the center of the solar system. In Babylon, the Sun god Shamash sat as judge of heaven and earth. Priests recorded his movements on clay tablets and read omens from his eclipses. Egyptian pharaohs claimed direct descent from Ra, the solar creator. The Sun was not a metaphor for power. It was power, made visible.
Greek astrology inherited this framework and refined it. Ptolemy's Tetrabiblos, written in the 2nd century CE, classified the Sun as the 'Great Luminary,' a source of warmth and dryness that governed a person's essential nature. The mythological split between Helios (who drove the solar chariot) and Apollo (god of reason, prophecy, and music) gave the astrological Sun its double character: raw vitality on one hand, conscious purpose on the other. Medieval astrologers called the Sun the king of the planets and assigned it rulership over gold, the heart, and the right eye.
The modern meaning of the Sun in astrology emerged in the early 20th century. British astrologer Alan Leo popularized Sun-sign columns in newspapers starting around 1915, reducing the complexity of a full birth chart to a single question: what sign was the Sun in when you were born? The move was controversial among serious astrologers, but it stuck. Today the Sun sign remains the most widely known piece of astrological identity. In psychological astrology, the Sun represents the conscious self, the ego, and the life path a person is growing toward.