What is a Stellium?
A Stellium occurs when 3 or more planets are conjunct with each other. This means that not only do you have 3 planets in the same sign, but they're also conjunct each other.
For example, if you have a planet A at 5 degrees of a sign, a planet B at 10 degrees of the same sign, and a planet C at 15 degrees, you would have a triple conjunction between planet A and B, planet A and C, and planet B and C. This is a Stellium.
What does a Stellium mean?
Someone with a stellium packs a punch, and the more planets there are, the more punch there is. Having a Stellium can be an odd thing to interpret as, one would think that if you have a concentration of planets in a given sign, you would embody this sign first and foremost, but it's usually not the case. Here's why. When you have a Stellium, you have a minimum of 3 conjunctions occurring, meaning that 3 planets or more are blending their energy with each other.
What are conjunctions?
Conjunctions represent skills, strengths, talents; they also represent a blend of energy which can denature the original sign.
Example: Let's say you have Mars in Capricorn, Moon in Capricorn, and Neptune in Capricorn. For a beginner, this looks like a heavy dose of Capricorn, right?
But it's not. This person is likely going to be very Neptunian, resembling Pisces energy. Simply because in terms of strength, Neptune is going to swallow whole Mars and Moon, giving them a very Piscean nature. If you're a beginner in Astrology, you would read your Moon in Capricorn interpretation. Surely, your Moon being in Capricorn does mean that you carry some of the traits and will resonate with some of the energy. But if your Moon is conjunct Neptune, it's a completely different story. You're way more empathic, soft, sensitive and romantic than your typical stoic/pragmatic Capricorn Moon.
But that's not it. This person would also probably have emotional reactions, which at times feel very Aries-like, simply because their Moon-Mars are forced to work together, giving them strong emotional responses.
Stellium in house
The house where the Stellium is located is also significant as there is going to be an overwhelming focus on the house's matters and energy. For example, if you have a 10th house Stellium, you will be preoccupied with success reputation and achievements just like a Capricorn would, probably even more! Because the planets tend to create such a strength, focus, and imbalance in a given direction, the person very much so feels a sense of purpose and like they have been invested in special skills and talents. It's important to learn how to decipher the conjunctions and how they work with each other as such a blend of energy can give a complex personality but with unusual gifts. As you can see, Stelliums are very rich and make for interesting and layered people; however, they can be much more difficult to interpret than meet the eye. Here are a few rules to help you out.
Interpreting a Stellium: Guidelines
Stellium: Find the leading planet.
The first thing to do is to figure out who's the leading planet. You have 3 planets or more fighting for leadership, who's the winner? Look at your rising sign. If your chart ruler is in the pack, good chances are it's the boss. You also need to understand the concept of dignities and planets' weight. For example, Moon is the most gentle planet, and if she's conjunct with a strong or aggressive planet, Moon is the one making sacrifices in this partnership. Outer planets pack a mean punch, and you can bet they more often than not take over the inner planets. Dignities and rulerships will help you determine who's the boss in your Stellium.
Stellium: Orbs allowed
Are your planets conjunct? In a Stellium, there are different rules. Let's say your Venus is at 14°, your Mercury at 19°, and your Mars at 25°. In a regular set-up, Sun and Mars aren't conjunct as there is 11 degrees separating them. In the case of a Stellium, Mercury is doing the link between the two planets, and Venus & Mars become conjunct. Now you're going to need to interpret these planets as separate conjunctions and as whole entity. This is a layered work of interpretation, micro and macro.
Stellium in house
With the Stellium you have a huge focus on a sign and a house. Which means that whatever House your Stellium falls in will be a huge focus in your life. Sometimes it takes some times to unravel, especially if the Stellium is in Capricorn or 10th house, it could take time for you to realize the energies in play.
Stellium: Finding balance
The struggle with a Stellium is that you will tend to neglect the opposite sign and house. It's a scale with all the pawns on the same side, but it's important for the overall life direction to keep in mind to always balance that Stellium of yours. You have a Stellium in the 10th? Don't forget that home and family are important, don't neglect them for your success. You have a Stellium in the 6th? It doesn't mean spirituality and creativity aren't important for your overall happiness. You see the point.
Transits to stellium
Well, with a Stellium it's going to be roller coasters. The positive transits will be felt on a way bigger level, and difficult transits will be a trip to hell-land. The good news is, when you receive challenging aspects, you'll get the chance to mature and learn valuable lessons all at once. You could become adult, wise, mature, way faster than others. Usually, the difficult transits will be experiences all at once, and once you passed that difficult milestone, you'll be good to go for a while. For you, the concept of "seasons" is very much relevant to your experiences.