What the calendar does settle
The Sun's longitude at noon on 9 September has ranged from about fifteen and nine tenths degrees of Virgo to seventeen and a third across the years from 1930 to 2035. That is the whole variation in more than a century, and it is small because the leap day keeps correcting the drift that the odd quarter day introduces.
From that position two things follow with no argument. The sign is Virgo, mutable earth under Mercury, and the decan is the second, the band from ten to twenty degrees that the Chaldean order gives to Venus. Both are facts about where the Sun was, not claims about the person, and both can be checked against any ephemeris.
The Moon, which has two answers
The Moon moves about thirteen degrees a day and changes sign every two and a half days or so. On a given 9 September it will occupy one sign for part of the day and the next for the rest, or occasionally sit in a third if the change falls awkwardly against your time zone.
That matters because in traditional practice the Moon carries the responsive and habitual side of a reading, and the two candidate signs on any particular year are usually in different elements. A person born in the morning and a person born at night, same date and same year, can be given readings that share the sun sign and disagree about almost everything else. No date based description can resolve this, which is why the ones that try tend to say nothing at all.
The rising sign, which has twelve
The eastern horizon sweeps through the entire zodiac once a day. Roughly every two hours a new sign begins to rise, so this birthday excludes none of the twelve, and only the clock time and the latitude of the birthplace decide which one applies.
Because the rising sign sets the first house, it also sets every other house cusp, and therefore which area of life each planet is read as belonging to. The same Virgo Sun near sixteen degrees can land in the tenth house for one person and in the fourth for another born the same afternoon. If a birth time is genuinely unavailable there are ways to narrow it, but a date will not do it.
Why this ordering is the right way round
The sun sign is the placement the greatest number of strangers share with you. Roughly one person in twelve has it, and everyone born within about a fortnight of you has it exactly. That is what makes it usable in conversation and also what makes it the least individual thing in a chart.
The parts that actually separate one birthday from another are the ones the date cannot supply. The widget above takes your year, hour and birthplace and returns the solar degree rather than a range, along with how far that fell from the nearest sign boundary. It is the difference between being told a category and being told a position.
None of that makes the sun sign useless. It is simply the first line of a chart rather than the whole of it, and the order in which the pieces are collected matters.
Questions people ask about this
What sign is 9 September?
Virgo, without qualification. The sign runs from around 22 or 23 August to around 22 or 23 September, so this date sits well inside it in every year.
What Moon sign goes with a 9 September birthday?
There is no fixed answer. The Moon changes sign every two and a half days, so this date allows two possibilities in most years and three in a few. The hour of birth decides.
Can I know my rising sign from my birthday?
No. All twelve signs rise on any given date, each for about two hours. The rising sign needs the clock time and the birthplace, not the calendar date.
What degree of Virgo is 9 September?
Between roughly sixteen and seventeen and a third degrees at noon, over the last hundred years. The widget above narrows that to a single figure using your own details.
Which decan is this birthday in?
The second decan of Virgo, ten to twenty degrees, ruled by Venus in the Chaldean scheme and by Mercury under the triplicity method.
Is the sun sign the most important placement?
Traditional practice does not rank it first. It is the most widely shared placement in any chart, which is part of why the Moon and the Ascendant usually carry more of what distinguishes one reading from another.