The short list of what is settled
Checked at noon in every year from 1930 to 2035, this date has been Gemini without exception. The Sun stands between about five and seven degrees of the sign, a range of roughly a degree and a half across the whole span, and it stays inside the first decan throughout.
That stability is a property of the calendar. Leap days pull the date back onto the same stretch of orbit every four years, so a birthday keeps its degree far more reliably than most people expect. It is one of the few things about a chart that can be stated from the date alone.
The other thing the date fixes is the season position. A 27 May Sun sits about a third of the way through Gemini season, well past the ingress and well short of the June solstice that ends it.
The much longer list of what is not
The Moon travels roughly thirteen degrees a day. On a given 27 May it sits in one sign, or crosses from one into the next partway through, and across a run of years every sign has taken a turn. Without a birth time and year the Moon sign is simply unknown.
The rising sign is worse. A full circle of the zodiac passes the eastern horizon every twenty four hours, so the Ascendant shifts by a whole sign roughly every two hours, and its rate depends on the latitude of the birthplace. Any of the twelve can rise on this date. The same applies to every house cusp in the chart, and therefore to where each planet lands by house.
The decan, which does follow from the date
Six degrees of Gemini falls in the opening decan, from zero to ten. The Chaldean sequence assigns that face to Jupiter, while the triplicity scheme keeps it with Gemini and Mercury.
Tradition reads the Jupiter version as Gemini broadened out, more inclined to the wider argument than the immediate exchange, and the Mercury version as the sign in its plainest form. These are readings rather than measurements, and they are the layer that separates one Gemini birthday from another, which is exactly the layer most pages about this date skip.
Neither reading is a prediction. They describe what the tradition has attached to a ten degree band, and they would change if the writer switched schemes, which is a good reason to treat them as commentary rather than as fact about the person.
Closing the gaps
The widget above turns the date into a position. Given a year, a time and a place it returns the Sun's degree and minute, the decan, and the distance to the nearest sign boundary, which on 27 May is several days of travel rather than a matter of hours.
If the birth time is unknown, the calculation defaults to noon. For the Sun that is harmless here, because the whole day sits inside the same sign and the same decan. For the Moon and the Ascendant it is not harmless at all, and those results should be treated as provisional until the time is found.
Where the hour cannot be recovered, a birth certificate, a hospital record or a family memory of the part of the day is usually enough to narrow the Ascendant to two or three candidates rather than twelve.
Questions people ask about this
What sign is 27 May?
Gemini, in every year sampled at noon since 1930. The date is far enough past the Taurus boundary that no year in the span puts it in doubt.
Can the date tell me my Moon sign?
No. The Moon changes sign every two and a half days or so, and over a hundred years of 27 May birthdays it has occupied all twelve. A year and an hour are needed to pin it down.
Can the date tell me my rising sign?
No. The Ascendant depends on the time and place of birth rather than the date, and it moves through a whole sign in roughly two hours. Any of the twelve is possible on 27 May.
Then what is the point of knowing the degree?
The degree decides which aspects the Sun makes to other planets, which decan it occupies, and how a progressed chart advances. It is the difference between a label and a position.
Is the sun sign the most important placement?
It is the most widely quoted, not the most personal. Everyone born within about a day of you shares it, while the Ascendant differs between people born a couple of hours apart in the same city.
How close is 27 May to a sign boundary?
Not close. The Sun entered Gemini around six days earlier and leaves it around three weeks later, so the position is comfortably interior and the year makes no difference to the sign.