What a stellium is
A stellium is a group of three or more planets in the same sign or the same house of a birth chart. So many planets in one place are read as a concentration of energy: the themes of that sign or house become a larger part of the person's life, with its strengths and its blind spots. The word is usually traced to the Latin stella, "star"; older books call it a satellitium.
How many planets make a stellium
Three is the usual minimum. Some astrologers want four, and some want the planets close together, each within a few degrees of the next, rather than anywhere in the sign. The calculator counts the ten planets, the Sun to Pluto. The lunar nodes, Chiron, Lilith and the angles (the Ascendant and Midheaven) are left out, though some astrologers add them. For each group it gives how many degrees it spans and whether every planet is within 8° of the next, a chain of conjunctions.
Planets bunched across a sign line, say at 28° Aries, 1° Taurus and 4° Taurus, aren't a stellium by sign, but some astrologers count a tight group like that anyway. The calculator lists those chains separately.
By sign and by house
A stellium by sign needs only the birth date, most of the time. The Moon changes sign every two or three days and the other planets far less often, so on most birthdays the signs are settled without a time. When one of them did change sign that day, the calculator says so and what difference the time makes.
A stellium by house needs the exact birth time and place, because the houses turn with the sky through the day. The two often overlap, but not always: two planets late in Capricorn and one early in Aquarius can share the 10th house without sharing a sign, and a stellium in one sign can be split between two houses.
How astrologers read a stellium
- The sign or house, turned up. Its qualities are strong in the person, and so are its blind spots. The sections below give the reading for each sign and each house.
- The ruler. The planet that rules the stellium's sign is read as the one that directs its energy, so where it sits matters. When the ruler is part of the stellium, it is read as stronger still.
- How tight it is. A group within about 10° is read as fusing its planets into one intense drive; a group spread across a whole sign as a theme rather than a single force.
- Personal or shared. The Sun, Moon, Mercury, Venus and Mars move fast, so a stellium that includes them is personal. Jupiter, Saturn, Uranus, Neptune and Pluto move slowly, and a group of them alone is shared by everyone born within months.
- What's left over. A chart with a big stellium has fewer planets elsewhere, so some signs and houses carry less of its energy.
These are readings from astrological tradition, for reflection rather than prediction.
Stelliums a generation shares
When three slow planets share a sign, everyone born in that span has the same stellium. From December 1988 to early February 1991, Saturn, Uranus and Neptune were all in Capricorn; for most of 2020, Jupiter, Saturn and Pluto were. Astrologers read a stellium like that as a generation's signature: it becomes personal when your Sun, Moon or another fast planet joins it, or when it falls on an angle of your chart. The table below lists every one since 1900.
Is it rare?
No. Counting the ten planets, about two births in three have at least three of them in one sign. About one in five has four or more, and about one in 25 has five or more. Those shares come from every day from 1950 to 2009, computed with the site's ephemeris. A stellium isn't a sign of a special chart; it is a clue to where a chart's energy gathers.