One answer at noon, for reasons of arithmetic
Gemini begins at sixty degrees of ecliptic longitude. Across the period covered here that crossing falls on 20 or 21 May, so by noon on the twenty second it has always already happened. There is no year in the set where noon on this date is still Taurus.
The boundary itself is not fixed, though. The tropical year is roughly a quarter of a day longer than a common calendar year, which pushes every ingress about six hours later than it was the year before, until a leap day pulls it back by around eighteen hours. Watched over ten years the Gemini ingress ranges across something close to a day and a half. It simply never wanders far enough forward to reach the twenty second at midday.
Why the birthplace is still worth entering
The Sun crosses into Gemini at one instant everywhere, and what differs is the clock reading people give that instant. A crossing at 01:00 UTC on 21 May is eight in the evening on the twentieth in New York and five in the afternoon in Los Angeles. The same sky, three calendar readings, and only one of them matches whatever range a reader happened to find.
Mismatched time zones are the ordinary cause of a wrongly reported sun sign, far more often than any exotic astronomical case. The widget above avoids it by working from the moment rather than the label. Give it the year, the hour and the birthplace and it returns the sign plus the number of hours between your birth and the crossing, so you can see for yourself how much room there was.
Nobody sits astride the line
The Taurus Gemini cusp appears in a great many descriptions, usually as a mixture of stubbornness and restlessness. The sky does not support the idea. At any instant the Sun has a single longitude, and that number is either short of sixty degrees or past it. A birth ten minutes before the crossing is wholly Taurus and one ten minutes after is wholly Gemini.
Read the word as a confession instead. It appears where a writer has a date and nothing else, and covering both signs is the only honest response to that. The moment your year, hour and city are known, there is no ambiguity left for the word to name.
How the two signs differ, and what they share
Taurus is fixed earth ruled by Venus, read as slow moving, physical and attached to what it already has. Gemini is mutable air ruled by Mercury, read as quick, verbal and easily redirected. They share no element, and the shift from fixed to mutable is a change from holding a position to trading it, so the two descriptions rarely get mistaken for each other.
Still, the practical difference for a chart is one placement. Everything else, the Moon, the Ascendant, the planets and the aspects between them, is unchanged by which side of this boundary the Sun landed on. If the answer is not the one you grew up quoting, what you have gained is an accurate line rather than a different personality.
Questions people ask about this
Is 22 May Taurus or Gemini?
Gemini. Taken at noon, every year from 1930 to 2035 has the Sun already past sixty degrees on this date. The widget above checks your specific year, hour and birthplace.
Why do some sources say Taurus runs to 21 or 22 May?
Because a printed range has to pick one date for a boundary that shifts by about a day and a half over a decade. Different publishers picked different years as their reference, so their ranges disagree.
Could a time zone make me a Taurus after all?
Only in an unusual case. The crossing normally sits well clear of noon on the twenty second, but since a far western time zone reads an earlier calendar day for the same instant, running the check costs nothing.
Am I on the Taurus Gemini cusp?
No, because there is nowhere to stand between two signs. Your Sun had one longitude at birth and it lay inside one of them. Cusp is a word for absent information about the birth.
Does my birth hour matter for this date?
Not for the sun sign here, since the boundary is a day or more away. It matters greatly for the Ascendant and the house positions, which move by a degree every four minutes.
Is a Sun at one degree of Gemini a weak Gemini?
No. The sign is fully in effect from its first minute. The exact degree governs which aspects form and which house the Sun occupies, not the strength of the sign.