Mercury
Mercury is the fastest of the seven classical planets and the one that ranges least far from the Sun. Its greatest elongation is limited to a little under 28 degrees, so it is never visible against a dark sky: it appears only as a dawn or dusk object, low over the horizon, for a matter of weeks at a time. It completes its own circuit of the Sun in about 88 days, and a full synodic cycle relative to the Sun, one evening apparition to the next, in about 116 days, the shortest of any planet. It turns retrograde three to four times a year, for about three weeks each time. The same low elongation is why Mercury is difficult to observe with the naked eye at all: the window in which it stands far enough from the Sun and high enough above the horizon to be seen is narrow, and depends on the observer’s latitude and the angle the ecliptic makes with the horizon at the time 1. None of this is in dispute; what has been made of it is another matter.
The names
The Greek descriptive epithet was Stilbon, “the Gleaming one.” As with the other four visible planets, the descriptive name is the older one in Greek use, and the mythological identification, with Hermes, came later 2.
In Akkadian the planet is UDU.IDIM.GU4.UD, an epithet usually read as meaning something close to “jumpy” or “darting,” describing the fast, irregular motion Mercury shows near the Sun. The same tradition also names it the star of Nabû, a god whose name is usually glossed as “announcer” or “herald” 2. The Latin name, Mercurius, survives directly in the Romance weekday names, mercredi, miércoles, mercoledì; the English name, Wednesday, instead preserves Woden, the Germanic figure onto whom the Roman weekday scheme was mapped.
Dignities
| Domicile | Gemini, Virgo |
|---|---|
| Detriment | Sagittarius, Pisces |
| Exaltation | Virgo, at 15 degrees |
| Fall | Pisces, at 15 degrees |
| Triplicity | Air (by night) |
| Bounds held (Egyptian) | Aries 12-20Taurus 8-14Gemini 0-6Cancer 13-19Leo 18-24Virgo 0-7Libra 6-14Scorpio 11-19Sagittarius 17-21Capricorn 0-7Aquarius 0-7Pisces 16-19 |
Mercury takes both Gemini and Virgo by domicile, and it is exalted in Virgo as well: the only planet in the whole scheme exalted in a sign it already rules, where every other planet is exalted as a guest Virgo. No source consulted for this entry resolves why. The full apparatus, including the parts of it that are textually contested, is set out in Essential Dignity.
Sect
Mercury does not have a fixed sect the way the other six planets do. It is diurnal when it rises before the Sun and appears as a morning star, and nocturnal when it rises after the Sun and appears as an evening star 3: the one planet among the seven whose sect is a computed fact about a particular chart rather than a fixed property of the planet itself. The general mechanics of sect are set out in Sect.
Tradition
Held byClaudius Ptolemy, Tetrabiblos bk. I ch. 4, Alexandria, c. 150 CE
Ptolemy places Mercury between the Sun and the sphere of the Moon in his physical scheme, and derives its changeable power from that position: “Mercury in general is found at certain times alike to be drying and absorptive of moisture, because he never is far removed in longitude from the heat of the sun; and again humidifying, because he is next above the sphere of the moon, which is closest to the earth; and to change quickly from one to the other, inspired as it were by the speed of his motion in the neighbourhood of the sun itself” 4 bk. I ch. 4. The doctrine of Mercury’s changeability, on this account, follows from where it sits in the planetary order.
Tradition
Held byWilliam Lilly, Christian Astrology bk. I, London, London, 1647
Lilly’s account of Mercury runs through the same fixed working template he applies to each planet: nature, colours, trades, parts of the body, diseases, places, and the kinds of person the planet is taken to signify, built for judging a client’s specific question 5 bk. I.
Gap in the evidence
A second Greek name for Mercury, transliterated Sekhes and said to descend from the same Akkadian epithet behind UDU.IDIM.GU4.UD, appears in some secondary literature. It has not been corroborated against an independent source, so it is recorded here as an unconfirmed claim.
Whether the “jumpy” or “darting” reading of that Akkadian epithet reflects how the name was understood at the time the surviving observational compendia were compiled, or is a later interpretive gloss on an older and by then opaque name, is not settled by anything consulted for this entry.
References
- Claudius Ptolemy, trans. F. E. Robbins. Tetrabiblos. Loeb Classical Library 435. Cambridge, MA: Harvard University Press, 1940 (composed c. 150 CE). bk. I ch. 4. find a copy (catalogue search) recordprimary source
The standard English reference and the chapter-numbering scheme this site adopts and names. Non-Robbins reprints number the chapters differently, so every locus here is given as Robbins numbering.
- Nicholas Campion. A History of Western Astrology, Volume I: The Ancient and Classical Worlds: Continuum, 2009. ISBN 9781441127372 recordscholarly
The standard single narrative survey. Volume I first appeared as The Dawn of Astrology, Hambledon Continuum, 2008. The subtitle is "The Ancient and Classical Worlds", not "The Ancient World"; the shortened form is widely miscited.
- Chris Brennan. Hellenistic Astrology: The Study of Fate and Fortune: Amor Fati Publications, 2017. ISBN 9780998588902 recordscholarly
A practitioner-scholar synthesis: comprehensive and well referenced, but not peer-reviewed philology. This site cites it with that characterisation.
- William Lilly. Christian Astrology. London, 1647 (composed 1647). bk. I. https://archive.org/details/b30338724 recordprimary source
Second edition 1659. Where a figure differs between the two printings this site says which printing it is quoting.
- Bradley E. Schaefer. Astronomy and the Limits of Vision. Vistas in Astronomy, 1993, 311-361. doi:10.1016/0083-6656(93)90113-X recordpeer reviewed
Volume 36. The standard visibility and atmospheric-extinction model for heliacal phenomena; a geometric altitude test alone will not predict first or last visibility of a star.