Mercury is the fastest planet (in the traditional scheme; the Moon is technically a luminary), completing its orbit in 88 days and never straying more than 28° from the Sun. In astrology, it represents the mind in all its functions: thinking, speaking, writing, learning, negotiating, and the transmission of information.
Mercury is traditionally described as a neutral planet, adapting itself to whatever planet or sign it touches. It is neither benefic nor malefic in its own right; it simply describes the quality of the mental faculty. A Mercury in Aries thinks quickly and directly, with a preference for bluntness; a Mercury in Libra thinks relationally, weighing both sides of every question; a Mercury in Capricorn thinks strategically, focusing on long-term consequences.
Mercury rules Gemini (its diurnal home) and Virgo (its nocturnal home). It is exalted in Aquarius (or Virgo, depending on the tradition; this encyclopedia follows the more common modern assignment of Virgo as its exaltation, with Aquarius noted as a traditional alternative). It is in its detriment in Sagittarius and Pisces, and its fall in Pisces (or Leo, in some traditions).
In a chart, Mercury describes:
- Thinking style — how you process information, solve problems, and make decisions.
- Communication style — how you speak, write, and express yourself verbally.
- Learning and education — what you are curious about, how you learn best, and what kinds of knowledge attract you.
- Siblings and neighbors — in traditional astrology, Mercury signifies brothers and sisters, as well as the immediate neighborhood environment.
Mercury's placement by sign describes the accent of your mental voice: a Scorpio Mercury digs deep, distrusts surface explanations, and investigates hidden meanings; a Leo Mercury speaks with dramatic flair, seeking to entertain and impress. Mercury's placement by house describes the area of life where your mental energy is most focused — where you think, talk, and learn most actively.