Mercury in Astrology: Communication, Retrograde Motion, Signs

Mercury in the sky

Mercury is the smallest planet of the Solar System and the one closest to the Sun. It goes round the Sun in about 88 days, which also makes it the fastest. Seen from the Earth, it never moves away from the Sun by more than 28 degrees: it can therefore only be glimpsed shortly before sunrise or after sunset, near the horizon, and for a short time. It is visible to the naked eye, but hard to spot.

A curious detail: Mercury rotates on its axis exactly three times for every two revolutions around the Sun, a so-called 3:2 resonance. A solar day there lasts about 176 Earth days, that is, two Mercurian years.

Hermes, Mercury and the caduceus

Its name comes from the Roman god Mercury, messenger of the gods, identified with the Greek Hermes. It is said to have received this name because of the speed with which the planet crosses the sky. Hermes is the god of travellers, merchants, messages and boundaries, and the patron of orators; he carries a staff entwined with serpents, the caduceus. In Western esoteric traditions, the figure of Hermes Trismegistus, a late fusion of Hermes and the Egyptian god Thoth, gave its name to Hermeticism.

Wednesday, mercury and alchemy

Wednesday owes its name to the Latin Mercurii dies, "day of Mercury". The liquid metal we now call mercury also bore this name in alchemy, where it was quicksilver, a symbol of what changes form and circulates. These connections are word and symbol games inherited from the Middle Ages and antiquity: they show how our ancestors ordered the world, not a property of the metal or of the planet.

Mercury returns to the same position relative to the Sun, as seen from the Earth, about every 116 days: this is its synodic period. This interval is the reason why its retrogrades recur several times a year.

What Mercury symbolises in astrology

In the birth chart, Mercury represents thought, speech, learning, curiosity, the analytical mind, the way one moves about, builds relationships, negotiates and writes. Astrologers associate it with siblings, neighbours, short journeys, contracts and trade. Tradition credits it with cunning, adaptability, humour and liveliness; its shadow is scattered attention or nervousness.

In Hellenistic tradition, Mercury is a "neutral" planet: it takes on the tone of the bodies with which it is in contact.

The signs linked to Mercury

See the portraits of Gemini and of Virgo.

Retrograde Mercury: an optical illusion

You will often hear "Mercury is retrograde" said about breakdowns, delays or misunderstandings. From an astronomical point of view, the retrograde motion is an optical effect: when Mercury, which is faster, catches up with and overtakes the Earth, the planet seems for a while to move backwards against the background of stars. It does not stop, and it does not truly move backwards. This happens about three to four times a year, for nearly three weeks each time. Venus and Mars (and the distant planets) also have apparent retrogrades.

In astrology, Mercury's retrogrades are traditionally associated with a period of rereading and revision: it is said to be inadvisable to sign a contract or start a project. In this very widespread form, it is a recent popular belief. No study has shown that communication errors increase during these periods. If the idea of "rereading" before signing helps you, it is harmless; but it is not a law.

Rhythms and reading in a chart

Mercury never strays far from the Sun: in a chart, it is therefore in the same sign as the Sun, or in the neighbouring sign before or after. It is never more than one sign away from it. To read it, one looks at its sign (the style of thought and speech), its house (the area in which one communicates) and its aspects (the relationships with other bodies); see the houses and the aspects.

An honest view of this reading

Mercury is a symbol: a way of naming how one thinks and expresses oneself. No physical mechanism links the position of a small planet to the way we speak. Use these images as a support for reflection, without looking in them for a prediction. See the history and limits of astrology.

Frequently asked questions

Also read

The meanings mentioned belong to tradition and symbolism. They are neither promises of results nor medical advice. Back to Guide to astrology basics.