Past the line, in every year
The Sun enters Scorpio when it reaches two hundred and ten degrees of ecliptic longitude, which happens around 23 October and moves by up to a day and a half between years. At noon in each year from 1930 to 2035, the Sun on 25 October stood between roughly one and two and a half degrees of Scorpio, so the crossing had already happened in all of them.
One degree of margin is about a day of solar motion, which is more than any variation in birth hour can absorb. The sign on this date is therefore settled in a way that the sign on the boundary dates themselves is not.
The distinction matters because the two cases get treated identically in most writing. A date a few hours from an ingress and a date two days past it are both described simply by naming a sign, which hides the fact that only one of the two answers could be overturned by a birth time. Stating the margin instead of the sign makes the difference visible immediately.
Why the small figure stays small
The degree is low because the date sits close behind the ingress, and it stays low for the same reason it stays put on any date. A common calendar year is about a quarter of a day shorter than the orbit, pushing the Sun's arrival roughly six hours later each year on the clock, and the leap day added every fourth February pulls the whole reckoning back by nearly a day.
Those two effects come close to cancelling over the four year cycle, leaving a residual swing of a little over a degree. The Gregorian rule that omits the leap day in 1900 and 2100 keeps the residual from accumulating, so the figure does not creep upward across generations.
The opening face of Scorpio
The first ten degrees of a sign form its opening face, and this position falls well inside it. The Chaldean order of the planets gives that band of Scorpio to Mars. The triplicity scheme divides the sign's faces among the water signs in order, which assigns the first to Scorpio itself, so the attribution follows whichever ruler you take for the sign.
That is where the modern and traditional accounts part company. Older practice reads Scorpio through Mars, while modern practice more often reads it through Pluto, and the two attributions carry very different associations. Both are interpretation rather than measurement, so a source quoting one ruler flatly has taken a position it should have declared.
What remains unresolved
Fixing the Sun uses up most of what a calendar date can tell you. The Moon crosses the zodiac in under a month, so on this date across different years it can be in any of the twelve signs, and within a single 25 October it moves far enough to change sign in many years. The ascendant turns through all twelve in twenty four hours and depends on the latitude of the birthplace as well as the hour.
So the sun sign is the widely shared part of a chart rather than the personal part. It groups together everyone born in the same stretch of the year, in any year, anywhere. The widget above uses your year, your hour and your birthplace to return the exact solar degree and the margin from that degree to the nearest sign boundary.
Questions people ask about this
Is 25 October Libra or Scorpio?
Scorpio, in every year checked at noon from 1930 to 2035. The Sun crossed into the sign around 23 October in all of them, leaving at least a degree of margin by this date.
What degree of Scorpio is this birthday?
Between about one and two and a half degrees at noon over that century. Your own figure depends on the year, the hour and the birthplace, which the widget above accounts for.
Can the birth time make this date Libra?
No. The Sun advances roughly a degree over a full day, which is less than the distance already covered past the boundary. The hour changes the degree, not the sign.
Which decan of Scorpio is 25 October?
The first, from zero to ten degrees. The Chaldean order gives it to Mars, and the triplicity scheme assigns it to Scorpio itself, so it follows whichever ruler you use for the sign.
Is Scorpio ruled by Mars or Pluto?
Traditional practice uses Mars, since Pluto was not known until 1930. Modern practice usually uses Pluto and often keeps Mars as a secondary ruler. Both are conventions rather than findings.
Does an early degree mean a weaker Scorpio?
No. A Sun at two degrees of Scorpio is fully in Scorpio. The degree affects aspects, house placement and the face, not whether the sign applies.