Saturn, or Uranus, depending on the text
Aquarius has two rulers in circulation. Classically it belongs to Saturn, which makes it a sign of rules held on principle; in modern practice it belongs to Uranus, which makes it a sign of sudden reversal. Both readings are used, sometimes in the same article, and the resulting descriptions of Aquarius contradict each other.
The consequence for compatibility writing is worth stating. If commentators cannot agree what governs the sign, a list of the signs it clashes with is not resting on much.
The hard angles
Leo lies 180 degrees from Aquarius; Taurus and Scorpio lie 90 degrees away on either side. Those are the only hard aspects to Aquarius, so the list is three names long by construction.
Aquarius, Leo, Taurus and Scorpio are the fixed signs, sitting in the settled middle of their seasons. Between any two of them a disagreement stabilises rather than resolving, which is the real mechanism behind everything the lists warn about.
Leo and Aquarius share a subject
The axis runs between the particular person and the general case: Leo's Sun against Saturn's rule, warmth for someone against fairness for everyone. Traditional readings treat this as two halves of one question, which is why long partnerships across the axis are ordinary.
The angle names the topic and no more. Whether the two halves fit together comfortably is not something 180 degrees can decide.
What squares describe, and what they omit
A square is 90 degrees between signs of one mode and incompatible elements, graded hard because it produces friction and friction produces movement. Taurus squares Aquarius from Venus and Scorpio from Mars, so the disputes differ in kind: one is about comfort defended, the other about intensity withheld.
What no list can register is orb. An Aquarius sun at one degree and a Scorpio sun at twenty-seven are not in a square at all. The contacts that reliably indicate strain are Saturn from one chart on the other's Moon or Venus, Neptune obscuring a personal planet, and hard Mars aspects that describe how a quarrel gathers pace. The synastry calculator measures the real separations, and synastry explains what is weighed.
Read the combination properly
The Aquarius and Leo page sets out what the two build together and where they lock, which a ranking cannot. It is the better read whichever way the list scored the pairing.
With both birth times to hand, compare the charts. The result frequently contradicts what the sun signs implied in both directions.
Questions people ask about this
Which signs are hard angles for Aquarius?
Leo opposite, Taurus and Scorpio square. All three are fixed signs, as Aquarius is.
Is Leo a bad match for Aquarius?
Not by the geometry. The axis divides one question between the individual and the collective, and partnerships across it are common.
What rules Aquarius?
Saturn traditionally, Uranus in modern practice, and the two produce conflicting descriptions of the sign.
What actually predicts difficulty?
Saturn and Neptune contacts to personal planets, hard Mars aspects, and how exact the angles are.