How Common Is a Stellium?

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A stellium is often presented as a rare signature. Whether it is depends almost entirely on the definition. This page takes the definitions already set out on what is a stellium and measures how often each one turns up in charts calculated with the free chart's own routines.

What the measurement found:

• Three or more planets in one sign is the majority case. 66.3% of the sampled dates had at least one sign holding three or more of the ten planets.
• Four or more is much less common: 18.7% of dates.
• Leaving out the Moon lowers both: 58.8% for three or more, 14.5% for four or more.
• Requiring a chain of conjunctions more than halves the three-planet figure, to 29.0%.
• Most stelliums lean on slow planets. Two or more of Jupiter, Saturn, Uranus, Neptune and Pluto shared a sign on 61.3% of dates, so a single personal planet joining them was enough to make three.

These are shares of dates in one sample, not shares of people. Common does not mean meaningless, and rare does not mean special.

Calculator note: the free birth chart shows each planet's sign in its table but does not flag or name stelliums. The grouping is something you do yourself. Ask the Astrologist does not compute these base rates.

The definitions measured

A short recap; the reasoning behind each is on what is a stellium.

1. Primary: three or more of the ten planets in one Tropical sign. The ten are the Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. The sign is the one the chart routines assign.
2. Four or more of the ten in one sign.
3. Without the Moon: the same two thresholds with the Moon removed. The Moon moves about 12° to 15° a day, so a noon Moon is valid for that one noon chart, not for the whole date.
4. Conjunction chain: the qualifying planets are in one sign and form one connected chain under the site's 8° conjunction orb. Every member must be reachable from every other through one or more links of 8° or less. Two separate close pairs in the same sign, far apart from each other, do not make a chain stellium.
5. Nodes and Chiron included, as a judgment-call sensitivity only: Chiron and both Mean Lunar Nodes counted alongside the ten. This is not a replacement definition. The angles are not counted in any view.

Two counting rules apply throughout. The largest group is the number of planets in the most populated sign, not the number of three-planet combinations inside it. The number of stelliums in a chart is the number of distinct signs that meet the threshold, so five planets in Virgo is one stellium, not ten overlapping triples.

The sample

One offline run of the free chart's own chart routines at code version a968bea: London (51.5074° N, 0.1278° W), 12:00 local clock time, one chart for every date from 1 January 1920 to 31 December 2059. That is 51,135 synthetic noon charts, the same sample as how many aspects a birth chart has and how common retrograde planets are. Noon is a fixed sampling instant, not a stand-in for an unknown birth time. Planet signs depend on the moment of the chart rather than the place, but the time of day still matters for the Moon, and real births are not spread evenly over dates.

How often each definition is met

The chain rule is the strictest change. Of the 33,914 dates with a three-planet sign stellium, 43.7% also had three planets linked by conjunctions; the rest were same-sign groups with gaps of more than 8° somewhere along them. Counting Chiron and the Nodes raises the rate the most, because each extra point is one more chance for a sign to reach three. That is why many astrologers treat those points as extra weight on a cluster that already qualifies rather than as members that can create one.

The largest group in one sign

The typical chart has a largest group of three. A largest group of one, with every planet in a different sign, occurred on 31 dates. Seven planets in one sign occurred on 12 dates in six clusters, among them 4 and 5 February 1962 (Sun, Moon, Mercury, Venus, Mars, Jupiter and Saturn in Aquarius) and 10 to 12 January 1994 (Sun, Moon, Mercury, Venus, Mars, Uranus and Neptune in Capricorn). Every seven-planet date included the Moon, and without it the largest group in the sample was six.

How many separate stelliums in one chart. With the primary rule, 33.7% of dates had none, 55.5% had one, 10.6% had two in different signs, and 0.2% (105 dates) had three. With four or more, 81.3% had none, 18.5% one and 0.2% (92 dates) two.

What the clusters are made of

Stelliums are not all alike, so the dates were also sorted by what the three-plus groups contained. These categories overlap: one group can belong to several, and a date with two stelliums can count in two different rows. Each is a share of all 51,135 dates.

For a breakdown that does not overlap, each individual stellium (one sign, three or more planets) was put in exactly one group. There were 39,563 of them across the sample:

Two mechanics produce most stelliums:

• The Sun, Mercury and Venus travel together. Mercury is never more than about 28° from the Sun and Venus never more than about 47°, so the three often share a sign. As a stand-alone group they are only part of the picture, 7.7% of stelliums in this sample.
• Slow planets sit in one sign for long periods. Two of Jupiter to Pluto shared a sign on 61.3% of the dates. On those dates, any one of the faster planets passing through that sign makes three. That is why 78.5% of all stelliums contained at least one slow planet. How long each planet stays in a sign is on how long each planet stays in a sign.

Cohort clusters: the same stellium for everyone born in a window

When three slow planets share a sign, everyone born in that window has the stellium, whatever their personal planets do. In this sample, three or more of Jupiter to Pluto shared a sign on 2,816 dates (5.5%). Measured as runs of consecutive sample dates, the longest were:

The Capricorn cluster of 1988 to 1991 is the one named on what is a stellium. These runs are cohort geometry: they say when the slow planets were grouped, not that any one person in that window is rare. A cohort stellium is read as shared background, the way outer-planet signs and generations describes, with the personal planets and houses showing how an individual meets it.

Worked example: Ruben's Capricorn group

Ruben is the fictional person whose chart is used on how to find aspect patterns: London, 5 January 1993, 12:00. Under the primary rule he has one stellium, four planets in Capricorn: the Sun at 15°10', Mercury at 4°25', Uranus at 17°56' and Neptune at 18°31'. No other sign holds more than one of his planets.

How each view treats it:

• Primary (3+) and 4+: yes, a four-planet stellium. Four or more in one sign occurred on 18.7% of the sampled dates.
• Without the Moon: unchanged. His Moon is in Gemini, outside the group.
• Conjunction chain: a chain of three, not four. The Sun, Uranus and Neptune are linked (Sun to Uranus 2.77°, Uranus to Neptune 0.59°), but Mercury is 10.75° from the Sun, the nearest of them, so it is in the sign without being joined to the chain. He meets the chain definition at three planets.
• Nodes and Chiron: no change. His South Node shares Gemini with the Moon, which makes two, and Chiron is alone in Leo.
• Composition: a group with two slow planets. Uranus and Neptune shared Capricorn on 2,629 sample dates between 15 February 1988 and 11 January 1996, so a Capricorn Sun or Mercury in those years was enough to complete a group like his. His Sun and Mercury are what make the cluster personal.

Read this way, Ruben's stellium is partly generational (Uranus and Neptune) and partly his own (the Sun and Mercury). Neither part makes it less real, and its four-planet size does not make it a mark of special destiny. The reading method is on how to interpret a stellium.

Why there is no house figure

A house stellium needs house cusps, and cusps depend on the exact birth time and place; Placidus houses also change width with latitude. A percentage taken from London at noon would describe London at noon, not charts in general, and a second sample place would just give a second arbitrary figure. So this page gives no house-stellium rate. If you know your birth time, you can check for one yourself; the difference between the two kinds is on stellium in a sign versus a stellium in a house.

What the numbers do and do not say

Base rates help set expectations. Under the loosest definition, a stellium is something most sampled dates had, so finding one in your chart is not by itself a rare signature. Under the stricter chain rule, or at four planets and more, it is a minority feature. Neither fact settles what the cluster means for you.

Astrologers usually read a stellium as a concentration of focus in one sign's style. A common type is not less meaningful for being common, and a rare one is not a sign of special destiny or fate. The base rate says how often the geometry occurs, nothing about events, health, relationships or money.

Checking your own chart

1. Open the free birth chart and read the sign of each of the ten planets in the table.
2. Count how many share each sign. Three or more in one sign meets the primary definition; four or more is the stricter count.
3. For the chain view, check that each planet in the group is within 8° of at least one other and that the links join them all.
4. Note which planets make up the group: the Sun, Mercury and Venus, the Moon, or slow planets shared with your birth cohort.
5. If your birth time is unknown, leave the Moon out and compare with the no-Moon rows.

Related articles

• How Many Aspects Does a Birth Chart Have?
• What Is a Stellium?
• Stellium in a Sign vs a Stellium in a House
• How to Interpret a Stellium
• Outer Planet Signs and Generations
• How Long Does Each Planet Stay in a Sign?