The degree, which barely moves
At noon in every year from 1930 to 2035, the Sun on 24 May has stood between about two point four and three point eight degrees of Gemini. That is a spread of roughly a degree and a half across more than a century, which surprises people who assume the sky drifts a great deal over a lifetime.
The leap year cycle is why. A tropical year is slightly longer than three hundred and sixty five days, so the Sun reaches a given point about six hours later each calendar year, and the extra day every fourth February hands those hours back. The position on a fixed date therefore traces a small repeating band rather than sliding away.
The practical consequence is that printed sign date ranges are rounded descriptions of that band. In the middle of a sign the rounding is harmless. Near a boundary it is where almost every disagreement about birthdays comes from, and a calculated degree removes the question rather than arguing about it.
The decan underneath the sign
Near three degrees puts the Sun in the first decan of Gemini, the band from zero to ten. The Chaldean order, running the visible planets from slowest to fastest around the zodiac, gives that band to Jupiter. The triplicity scheme assigns the decans of a sign to the three signs of its element in turn, so Gemini takes Gemini, Libra and Aquarius, and the first decan returns Mercury.
Naming both is the accurate thing to do. Under Jupiter the tradition reads the band as broad in scope and inclined to range widely; under Mercury it repeats the sign's own ruler and is read as concentrated Gemini. These are readings from different lineages, not competing measurements, and the degree they sit on is the same either way.
What Mercury ruling the sign means
Gemini is mutable air under Mercury. Mutable places it at the close of spring, adapting rather than sustaining. Air groups it with Libra and Aquarius, which the tradition reads as the signs of connection and exchange. Mercury as ruler brings language, movement and the handling of information.
Because Mercury rules the sign, its own position is treated as carrying the Sun's affairs. Mercury never strays far from the Sun and so is often in Taurus, Gemini or Cancer for a late May birth, but which one depends on the year and cannot be read off the date.
The hour holds the rest
The Moon crosses about thirteen degrees a day, more than a third of a sign, so it can change sign inside a single 24 May and two Moon signs stay in play until a time is given. The rising sign runs through all twelve in twenty four hours, changing roughly every two, and the whole house structure follows from it.
That is the real proportion of things. A date settles one body precisely. A time and a place settle the rest. Anyone describing your character from the date alone is working from the placement you share with everyone born in the same month, which is the least individual thing in the chart.
Time zone belongs in that calculation as much as the hour. The Moon changes sign at a single global instant and only the local clock differs, so identical wall clock times in different countries can fall on opposite sides of it. Supplying the birthplace is what removes the most common source of a wrong Moon sign.
Questions people ask about this
What sign is 24 May?
Gemini, without qualification. The Sun leaves Taurus around 20 or 21 May, so this date sits about three days inside Gemini in every year sampled from 1930 to 2035.
How far into Gemini is the Sun?
Between roughly two point four and three point eight degrees at noon, depending on the year. The widget above narrows that using your hour and birthplace.
Which decan does 24 May fall in?
The first decan of Gemini, from zero to ten degrees. The Chaldean order gives it to Jupiter and the triplicity scheme gives it to Mercury, so the answer depends on which tradition you are using.
Why do the two decan schemes disagree?
They are built on different logic. One deals the visible planets around the zodiac by speed, the other walks the signs of each element in order. Neither is a measurement, so both are reported here.
What sign is my Mercury?
Most likely Taurus, Gemini or Cancer, since Mercury stays within about a sign of the Sun. The year decides which, and a birth chart calculation settles it.
Do I need a birth time to get anything useful?
Not for the Sun, the degree or the decan, which the date supplies on its own. The Moon, the rising sign and the houses all need the time, and they carry most of the individual detail.