Oh...
The Aries stellium is indeed my Sun, Merc, and Venus. I have 3 planets in Capricorn in the 7th house though (Satu, Uran, Nept) so now those are a stellium but the Aries planets are not?
I suppose it depends on who you talk to. Here are a few quotes from Cunningham's article (with my editing for brevity):
"A stellium consists of several planets in 30 degrees or less of the zodiac."
(Hmm, I always thought they at least had to be in the same sign.)
"The classic rule was four planets, of which two had to be other than Sun, Mercury or Venus."
"Modern interpretations lean toward accepting three planets as a stellium. We're especially tempted to view it as one when it involves a multiple conjunction. The orb for a conjunction is usually 8 degrees but can be extended to 10 degrees in a multiple conjunction. The resulting focus of energy has nearly as much impact as a stellium - and a stellium that includes a multiple conjunction is more potent than one that does not."
"Stelliums involving conjunctions between the outermost planets - Saturn, Uranus, Neptune and Pluto - are highly memorable but complicated to manage. They represent a life-long learning curve!"
"To generalize, here are some criteria that contribute to or detract from its strength:
- the number of planets involved - four minimum; the more the stronger
- when the planets are far apart with no conjunctions, its weaker
- the number of planets in a particular sign - split into two signs makes it weaker
- the number of planets in a particular house - split into two houses makes it weaker
- when all of the planets in a stellium are in the same sign
and house, it's stronger
- when stellium planets are conjunct the Sun, Moon, Ascendant or Midheaven they're stronger
- when a multiple conjunction is present, the stellium is strengthened."
I don't know how much of this is "standard parlance" for the astrological community. I've never been too sure about my "multiple conjunction" - Sun, Mercury,Venus in Cancer, Uranus in Gemini, all within 8 degrees in the 8th house. While I do read it as a conjunction of all four since the Sun sits on the midpoint of the configuration, I've tended to give Uranus more importance as the "planet of oriental appearance" than as a significant contributor to the conjunction. It certainly presaged my strong interest in astrology! On the other hand, I'd have no trouble taking my son's cross-sign stellium, with Sun, Mercury and Saturn closely conjunct in early Scorpio and Pluto at 29 Libra 39, all within 7 degrees of one another.