Four degrees, and why it hardly moves
A sign is thirty degrees wide, and saying someone is Gemini only narrows their Sun to that thirty degree strip. On 25 May, taken at noon in every year from 1930 to 2035, the Sun has stayed between about three and five degrees of Gemini. That is a band of roughly a degree and a half across more than a century.
The reason is the leap year rule. The tropical year is a little under three hundred and sixty five and a quarter days, so each ordinary year the Sun reaches a given longitude about six hours later by the clock, and each leap day pulls it back by a full day. The two effects cancel over a four year cycle, and the date stays pinned to the same short stretch of the orbit.
That is why a birthday degree is worth quoting at all. It is not a vague average across a century, it is a genuinely narrow window, and the only thing that moves it much is the hour of birth, which shifts the Sun by less than a degree across a whole day.
The opening third of the sign
Each sign divides into three bands of ten degrees, called decans or faces. Four degrees of Gemini falls in the first, which runs from the ingress to ten degrees and covers roughly 21 May to 31 May.
Two rulership schemes apply to it and they disagree. The Chaldean order runs Mars, Sun, Venus, Mercury, Moon, Saturn, Jupiter in a loop from zero degrees of Aries, and counted through, this face lands on Jupiter. The triplicity scheme instead gives each sign's decans to the signs of its own element in order, so the first air decan stays with Gemini and therefore with Mercury. Tradition reads the Jupiter version as the broader and more expansive end of Gemini and the Mercury version as the sign at its most characteristic. Which reading you get depends entirely on which scheme the writer was using, and good sources say which.
What this date leaves completely open
The Moon covers about thirteen degrees a day, so on any single 25 May it passes through one sign or crosses into a second, and across different years it has been in all twelve. The date alone cannot narrow it.
The rising sign is looser still. The whole zodiac turns past the horizon in a day, so a birth hour and a birth place decide it, and any of the twelve is available on this date. The Sun is genuinely the least personal placement in a chart, because it is the one thing everyone born within a day of you shares.
Two people born on the same 25 May twelve hours apart have Suns within half a degree of each other and can have different Moon signs, different rising signs and every planet in a different house. The date settles the smallest part of the picture.
Why other pages about this date all read the same
Most birthday pages are built from a table of date ranges and a stock paragraph per sign. That produces a correct sign and nothing else, which is why they agree with each other and say very little.
The widget above works from a position rather than a range. Give it your year, your hour and your birthplace and it returns the exact degree and minute of your Sun, the decan it falls in, and how far that position sits from the nearest sign boundary. On this date the distance from the boundary will be comfortable, which is itself worth knowing.
Questions people ask about this
Is 25 May always Gemini?
At noon it has been Gemini in every year from 1930 to 2035. The Sun enters Gemini around 20 or 21 May, so by the twenty fifth it is several days clear of the boundary and no year in that span puts the date in Taurus.
What degree is the Sun on 25 May?
Between about three and five degrees of Gemini, depending on the year and the hour. The widget above narrows that to a single figure once it has your birth details.
Which decan is a 25 May birthday?
The first decan of Gemini, which runs from zero to ten degrees. The Chaldean order gives that face to Jupiter and the triplicity scheme gives it to Gemini itself, and so to Mercury.
Do I need my birth time for this date?
Not for the sun sign, which is settled by the date. You need it for the rising sign, for the house positions and for the Moon in years where it changes sign during the day.
Does a low degree mean a weaker Gemini?
No. A Sun at four degrees is as much in Gemini as one at twenty four. The degree matters for aspects, for house placement and for progressions, not for whether the sign applies.
Why does my birthplace matter if the sign is fixed?
It does not change the sun sign here, but it sets the local time of birth against a global clock, and it fixes the horizon. Both are needed for the rising sign and the houses.