Late in the sign, not near the line
Aries runs from zero to thirty degrees, and the Sun crosses that arc at roughly one degree a day. A position at twenty two degrees therefore has about eight days of travel left before the boundary, which is not a marginal case by any measure.
The confusion comes from cusp writing, which treats the last stretch of a sign as a blend with the next. There is no blend. At any instant the Sun sits at one longitude, and that longitude lies inside one sign. What the word cusp usually describes is missing information about a birth, and there is no missing information here.
The final band of Aries
The sign's third ten degree band opens at twenty degrees, and at noon between 1930 and 2035 this date has fallen between roughly twenty one and three quarters and twenty three degrees. Every year in the sample is inside the band, so the date settles it without a birth time.
The Chaldean order gives that band to Venus and the triplicity scheme gives it to Jupiter, so the ruler depends on the source. The tradition reads a Venus band in Aries as the sign's directness turned toward appetite and company, and a Jupiter band as the same directness turned outward and enlarged. Both are inherited descriptions, not measurements.
So the band is a fact about the date and the character attached to it is a convention. Reading the two the same way is the mistake most birthday pages make silently.
How steady the position is
Across more than a century the noon figure for 12 April has moved within about a degree and a quarter. Each ordinary year adds roughly a quarter of a degree and each leap day removes almost the whole accumulation, so the position oscillates rather than drifting.
That is why a date can settle a sign and a band while still being unable to give a single exact degree. The window is narrow, and a specific year and hour close it to one figure.
Anyone wanting a single figure should take it from a calculation rather than a table of dates, since a table cannot resolve below the level of the sign.
Where the real variation lives
Between two people born on this date, the Suns will agree to within a degree. Almost everything else can differ. The Moon covers between twelve and fifteen degrees a day, so it may be in either of two signs across the twenty four hours. The rising sign passes through all twelve as the Earth turns, changing about a degree every four minutes and varying with latitude.
Every house cusp is anchored to that horizon, which means the whole house structure of a chart is undetermined by the date. The widget above computes the exact solar degree for a year and birthplace, returns the Moon and Ascendant from a birth time, and reports how far the birth fell from the nearest sign boundary.
Questions people ask about this
Am I on the Aries Taurus cusp on 12 April?
No. The Sun is around twenty two degrees of Aries, about eight days of travel from the boundary. Cusp language describes uncertainty about a birth, and there is none on this date.
Which decan is a 12 April birthday in?
The third decan of Aries, from twenty to thirty degrees. Every year sampled at noon over the last century falls inside it, so a birth time is not needed to settle the band.
Who rules that decan?
Venus in the Chaldean order and Jupiter under the triplicity scheme. The two systems name different planets for this band, and neither claim rests on an observation.
What degree is the Sun on 12 April?
Close to twenty two degrees of Aries, within a window of about a degree and a quarter across the century from 1930 to 2035.
Does a late sign position mean a weaker sun sign?
No. A Sun at twenty nine degrees is as much in its sign as one at one degree. Degree matters for aspects and for house placement, not for membership.
What can two people born on this date disagree about?
The Moon sign, the rising sign, every house cusp and the placement of every planet other than the Sun. The date decides one position and leaves the rest open.