Stellium Meaning in Astrology
A stellium is a gathering of three or more planets in a single sign or a single house of the natal chart. The concentration puts a large share of the chart's weight into one place, so that the affairs of that sign and house, and the planet ruling them, dominate the life. The older term is satellitium; stellium is the modern form and the one in use.
How many planets count
Three is the threshold most of the modern tradition uses. Some astrologers require four, on the ground that three planets in one sign is common enough to be unremarkable, and the Sun with Mercury and Venus, which never travel far from it, makes three without any special concentration. What is counted are the seven traditional planets, the Sun and Moon among them, and the three outer planets. The angles, the Nodes, Chiron, and the asteroids are not planets and are not counted, though their presence in the same sign adds to the reading.
A stellium by sign and a stellium by house are distinct. With whole sign houses they coincide; with a quadrant system such as Placidus, three planets in one sign may lie across two houses, and the house stellium is the one that describes events. The planets need not be conjunct one another. Four planets spread across the thirty degrees of a sign form a stellium by sign though only the closest pair is within orb of conjunction; the tighter the cluster, the more the planets act as one.
How it is read
The reading begins with the house, since the house says where in life the concentration falls. A stellium in the tenth makes career and public standing the field of the whole life; in the seventh, the marriage and the partnerships; in the twelfth, seclusion, illness, hidden matters, and work done out of sight. The sign then says in what manner.
Next is the ruler of the sign. Every planet in the stellium is disposed by that ruler, and the ruler's own condition, its sign, house, dignity, and aspects, governs how well the concentration is delivered. A Virgo stellium with Mercury strong in Virgo among its planets is self-contained and effective; the same stellium with Mercury in Pisces, its detriment and fall, in the twelfth house, is a great deal of energy poorly directed.
Then each planet by dignity and by its relation to the Sun. A stellium usually contains the Sun, and planets within about eight degrees of it are combust, weakened, and hidden in its light; Mercury and Venus are the usual casualties. Saturn or Mars in a stellium bring the malefic's difficulty to every planet they touch; Jupiter or Venus bring ease. The Moon in a stellium ties the whole cluster to the emotional life and to the mother.
Last, the rest of the chart. A stellium is heavy, and whatever aspects it from elsewhere, a square from Saturn or an opposition from Mars, is felt by all of it at once. Transits to it are felt as a series: an outer planet crossing four natal planets in one sign produces several years of related events, one contact after another. Marc Edmund Jones's chart patterns describe the extreme case, the bundle, in which every planet lies within one third of the zodiac.
What it signifies in the life
The tradition reads a stellium as focus at the cost of range. The person has one department of life in which they are unusually invested and capable, and the other departments are thin: the planets gathered in one place leave other houses empty, and those houses' affairs are run by rulers that are elsewhere. Whether this makes for mastery or obsession depends on the ruler's condition and on the malefics. A well-disposed stellium is a vocation. An afflicted one is the place where the life's difficulties cluster and repeat, and the reading says so plainly, naming the house and the planet that afflicts.
In Jyotisha
Vedic astrology counts the same concentration in the rashi chart and reads it by house lord, by the strength of the grahas, and by the yogas they form. Several planets in one bhava are read through the lord of that bhava and through their conjunction with one another, since planets in one sign are conjunct in the Vedic sense whatever their degrees. Varahamihira's Brihat Jataka treats the case of four or more planets in one house, at least one of them strong, in its account of pravrajya yoga, the yogas of renunciation, holding that such a concentration can withdraw the person from ordinary worldly life into the order that corresponds to the strongest planet. The Navamsa and the running dasha are then consulted: a stellium's promise, for good or ill, is delivered in the dashas of its planets.