One year out of the whole run
A tally of one hundred and five to one is about as close to settled as a boundary date gets without being settled. The lone Gemini year is not a rounding artefact or a bad ephemeris. It is the year in which the ingress happened to arrive early enough to be past by noon.
The reason such a year exists at all is that the boundary does not stay put. The tropical year runs roughly a quarter of a day longer than the calendar year, so the moment the Sun reaches sixty degrees of ecliptic longitude falls about six hours later with each year that passes, then jumps back some eighteen hours when a leap day is added. Across a decade the ingress sweeps over about a day and a half. Twenty May sits at the very edge of that sweep, close enough to be caught once in a long century.
How far from the line you were born
Even in the Taurus years, the margin can be a matter of hours rather than days, and hours are exactly where time zones do their damage. The ingress is one instant worldwide. If it falls at 03:00 UTC on 21 May, that is late on the evening of the twentieth across North America, so an evening birth in Toronto is Gemini while a birth at the same absolute moment in Rome is still Taurus.
This is the ordinary way a sun sign gets reported wrongly: a date is read off a certificate, matched against a range that quietly assumed one time zone, and the birthplace is never consulted. A record that says only the day is missing the two facts that decide the case. The widget above avoids the whole problem by working from your year, hour and birthplace, and it reports how many hours from the boundary the birth actually fell.
The cusp describes a gap, not a person
Descriptions of a Taurus Gemini cusp usually promise a personality that is grounded and restless at the same time. The Sun offers no support for that. At any second it occupies one ecliptic longitude, which is either below sixty degrees or above it, and there is no window in which it is partly in each sign. Two hours before the change the placement is wholly Taurus, and two hours after it is wholly Gemini.
So a cusp is best understood as a note about what nobody looked up. It records that the year, the hour or the place was unavailable, and it stops being relevant once those are known. A birth minutes from the change is no less firmly placed than one in the middle of a sign.
Fixed earth beside mutable air
Taurus is fixed earth under Venus; Gemini is mutable air under Mercury. Modality, element and ruler all differ and there is no shared traditional ruler between them, so the two answers here really do read differently. Taurus is described as settling into what works and resisting revision; Gemini as sampling widely and revising constantly.
The popular versions still exaggerate. Both signs are read as strongly sensory rather than abstract, one through touch and material comfort, the other through talk and information, and neither is credited with much patience for grand theory. The gap is in tempo more than in temperament.
If the answer comes back as the sign you did not expect, very little follows from it. The Sun is one placement among many, and the Moon, the Ascendant, the planets and the houses are all calculated the same way whichever side of the line you landed on.
Questions people ask about this
Is 20 May Taurus or Gemini?
Taurus in one hundred and five of the years from 1930 to 2035 measured at noon, and Gemini in one. The odds strongly favour Taurus, but the exception is real.
Which year on this date came out Gemini?
It is the single year in that run where the ingress arrived before midday. Rather than matching your year against a list, the widget above computes the position directly for the year you give it.
Do I need my exact birth time?
It helps, because in several of the Taurus years the boundary arrives later the same day. A birth late on 20 May can be Gemini even in a year that reads Taurus at noon.
Am I a Taurus Gemini cusp?
No. A cusp is not an astronomical state. The Sun holds one longitude at a time and that longitude lies inside a single sign, so the word marks missing detail rather than a mixture.
Why do published ranges end Taurus on different days?
Because they compress a moving boundary into a fixed date and each publisher rounds it their own way. Many were also computed for one time zone and never adjusted.
Does being at the end of Taurus dilute the sign?
No. A Sun at twenty nine degrees of Taurus is as much in Taurus as one at five. The precise degree matters for aspects and house cusps, not for whether the sign counts.