How steady a birthday degree really is
People tend to assume that because sign start dates wobble between the twentieth and the twenty first of a month, the Sun's position on an ordinary date must wobble as well. It barely does. On 28 May at noon, across the whole of 1930 to 2035, the Sun has stood between about six and eight degrees of Gemini.
A degree and a half of drift over a century is the leap year cycle doing its job. Each common year the Sun arrives at a given longitude about six hours later than the year before, and the leap day resets that accumulation. The wobble that shows up at sign boundaries is the same wobble, but it only becomes visible when a boundary happens to sit inside it.
On 28 May there is no boundary anywhere near the drift, so the wobble has nothing to reveal. The practical result is that anyone born on this date in any year of the last century can be given a degree before they say which year it was.
Seven degrees inside the opening decan
Gemini's first decan runs from the ingress to ten degrees, so a 28 May Sun is well inside it with a couple of degrees to spare before the next band begins. The Chaldean count gives this face to Jupiter, the triplicity scheme keeps it with Gemini and Mercury.
Where the two schemes disagree, the sensible course is to note both and say which one a description came from. Tradition reads a Jupiter face in an air sign as the wider, more general form of the sign's habit, and a sign's own face as its plainest expression. Either way the Sun is in Gemini and the face is a second layer, not a replacement.
What the same date leaves undecided
The Moon can be in one of two signs during a 28 May, depending on the hour, and over a span of years it has been in all twelve. The Ascendant is decided by the clock and the map rather than the calendar, and every sign is available.
This is the part worth taking seriously. Two people born on the same 28 May, one at dawn and one at dusk, share a Sun to within a fraction of a degree and can share almost nothing else in the structure of their charts.
That is the ordinary case rather than an edge case. The Ascendant advances through a full sign in roughly two hours, so twelve hours of separation guarantees a different rising sign and a completely different arrangement of houses.
Getting your own figure
The widget above computes the Sun's longitude for your own year, hour and birthplace, rather than reading a sign off a date range. It reports the degree and minute, the decan, and how far the position sits from the nearest sign boundary.
On this date that last figure will come back comfortably wide, which is a useful thing to have confirmed rather than assumed. It is also the number that matters if you were ever told you were a cusp birth, since a wide margin closes that question completely.
Nothing here predicts anything about a life. It fixes a position, names the band that position falls in, and marks the traditional readings of that band as readings rather than measurements.
Questions people ask about this
Is 28 May Gemini or Taurus?
Gemini, at noon in every year from 1930 to 2035. The Sun leaves Taurus around 20 or 21 May, so by the twenty eighth there is a week of margin and no year in the span changes the answer.
What degree of Gemini is 28 May?
Between about six and eight, depending on the year and the hour of birth. The widget above narrows that to a single degree and minute from your own details.
Which decan does the date fall in?
The first decan of Gemini, from zero to ten degrees. Its ruler is Jupiter under the Chaldean order and Mercury under the triplicity scheme, since that face belongs to Gemini itself.
Why does the degree hardly change between years?
Because the leap year rule keeps the calendar in step with the orbit. The six hour annual slippage accumulates for three years and is cancelled by the leap day, so the date returns to nearly the same solar longitude.
Do I still need a birth time?
For the Sun, no, since the whole day sits in one sign and one decan. For the Moon, the Ascendant and the houses, yes, and without it those parts of a chart are guesses.
Is being at seven degrees significant in itself?
It matters for aspects and for progressions, because both depend on exact longitude rather than on the sign label. Tradition attaches no special quality to the number by itself.