Astrologers get their understanding of the planets from many sources, including science, mythology, and the astrological tradition.
In astronomy, the little planet Mercury is distinguished by its rapid pace — it whirls around the Sun in a mere 88 days — and its proximity to the Sun.
In mythology, the Roman god Mercury, known to the Greeks as Hermes (Ἑρμῆς), is also recognised for his speed. In his winged sandals and cap, he was the messenger of the gods as well as a thief, musician, trickster, and accomplished liar who could talk his way out of anything. A master of spin, Hermes escorted dead souls into the underworld. The ancients worshipped him as the god of travel, speech, roads, boundaries, sleep, dream, and the nameless places that fall between here and there. Two of those in-between spots deserve special recognition: the shadowy realm between wakefulness and sleep, and the transition between life and death.
Astronomical Facts
Mercury is the smallest and innermost planet in the Solar System. Its orbit around the Sun takes 87.97 Earth days, the shortest of all the planets in the Solar System. Like Venus, Mercury orbits the Sun within Earth's orbit as an inferior planet, and its apparent distance from the Sun as viewed from Earth never exceeds 28°. This proximity to the Sun means the planet can only be seen near the western horizon after sunset or eastern horizon before sunrise, usually in twilight. At this time, it may appear as a bright star-like object, but is often far more difficult to observe than Venus. The planet telescopically displays the complete range of phases, similar to Venus and the Moon, as it moves in its inner orbit relative to Earth, which recurs over its synodic period of approximately 116 days.
Mercury rotates in a way that is unique in the Solar System. It is tidally locked with the Sun in a 3:2 spin–orbit resonance, meaning that relative to the fixed stars, it rotates on its axis exactly three times for every two revolutions it makes around the Sun. As seen from the Sun, in a frame of reference that rotates with the orbital motion, it appears to rotate only once every two Mercurian years. An observer on Mercury would therefore see only one day every two Mercurian years.
MERCURY IN ASTROLOGY
The symbol of Mercury: 
Mercury’s symbol has three metaphysical components: the cross of earth or matter, the circle of spirit, and, perched on top, the crescent of personality looking like a tiny satellite dish, ready to receive information.
KEYWORDS
Babble, Communication, Connection, Cunning, Deceit, Exchange, Intelligence, Lies, Logic, Mobility, Nervousness, Practicality, Superficiality.
Understanding Mercury
Mercury symbolises your style of communication, your reasoning ability, speech, writing, knowledge, the intellect, wit, and learning. Its position in your birth chart determines the way you think, the speed with which you gather facts and process information, the style with which you express yourself, and your ability to tell a story (truthful or otherwise), give a speech, and use language.
Because it orbits the Sun so closely, Mercury is always either in the same sign as the Sun or in an adjacent sign — and in no case is it ever more than 28° away from the Sun. If Mercury is anywhere else, you’re reading the tables or the horoscope wrong.
Mercury symbolises everything related to the following concepts:
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- The connection between the vital energies and the body (Nervous system)
- The mental connections which make thinking possible
- Neuronal connections in the brain
- Verbal connections, which make speaking possible
- Communication on a human level
- Exchange of thoughts resulting from this communication
- As a consequence of exchange with the environment, the resulting adaptation of the individual to it
- Intelligence and Conscious Thought
- Trade, short travels, transport and fraud
- Toddlers and children
- All things which facilitate communication: telephones, postal service, web, radio, television, etc.
As can be seen in this list, “communication” is really not the most basic of meanings for Mercury - though this is often written - but rather the idea of “connection” – although the verbal form, “to connect”, may be more appropriate, as it would underline the fact that Mercury, like all the planets, represents an active principle.
Mercury rules the signs of Gemini and Virgo.
Mercury in the Signs
Mercury’s position in natal horoscopes determines the way you think, the speed with which you gather facts and process information. You can read more here!
Mercury in the Houses
Mercury is the planet of communication. Its position by house suggests those areas in life that most absorb your mind and stimulate your thoughts. You can read more Mercury in the Houses!