The Sun is one of the two lights of traditional astrology and the ruler of Leo. As the visible source of day it is central to the horoscope, its place fixing the sign a person is most often said to be "born under." The same round glyph that marks its place in a birth chart also marked gold in the parallel, older sign-system of alchemy, where each of the seven classical planets stood for one of the seven metals then known to European craft: the Sun for gold, the Moon for silver, Mercury for quicksilver, Venus for copper, Mars for iron, Jupiter for tin and Saturn for lead.
The pairing rested on the Hermetic principle "as above, so below," and by the sixteenth century it had stabilised widely enough that a single circular sign could denote a planet in an ephemeris and a metal on an apothecary's shelf to the same trained reader. The correspondence also survives, opaquely, in the calendar: the Romance-language weekday for Sunday descends from the Latin for the Sun's own day, just as Monday preserves the Moon's, part of a seven-day planetary week that late antiquity inherited from the same astrological tradition that fixed the glyph itself. No other classical planet carries quite this dual life, at once the ruling body of a zodiac sign, the namesake of a day, and the sign of a precious metal, three separate symbolic systems reading the identical circle-and-dot mark in three different registers depending on the book in front of the reader.