The position and its band
At noon between 1930 and 2035 the Sun on this date has stood between about twenty and seven tenths degrees of Virgo and roughly twenty two and a tenth. Every one of those figures is above the twenty degree line, so unlike the two days before it, this birthday does not need a conditional answer about the decan.
The range stays inside one and a half degrees because the calendar corrects itself. The quarter day the year runs long pushes the date forward against the Sun for three years, and the leap day pulls it back. Nothing accumulates, and the same date keeps landing in nearly the same place across generations.
Mercury twice over
The Chaldean order deals the seven visible planets, slowest to fastest, one to each ten degree band, running continuously from the start of Aries. Counted through, the final band of Virgo comes back to Mercury, which also rules the whole sign.
Older texts treat that repetition as intensification. The band is described as Virgo at its most itself, where the discriminating and analytic side of the sign is not tempered by a second planet's flavour. That is a traditional reading rather than a finding, and it is worth keeping labelled as one. The triplicity scheme disagrees anyway, assigning this band to Saturn on the grounds that Capricorn is the third earth sign, which produces a noticeably more austere description of the same ten degrees.
The sign, without hedging
Virgo ends at one hundred and eighty degrees of longitude, which the Sun reaches around 22 or 23 September. That leaves this birthday more than a week clear of the boundary, and the boundary itself only shifts by hours between years.
So there is no useful sense in which a 14 September birth is near Libra. It is Virgo whatever the hour, whatever the time zone and whatever the year. The only thing worth calculating is the exact degree, because that is what decides the aspects the Sun makes and, once a birth time is known, which house it occupies.
What a birthday cannot supply
The Moon changes sign every two and a half days, so on any 14 September it will be in one of two signs and occasionally a third. The rising sign turns through all twelve in a day, about two hours each, so the date rules nothing out and the hour rules everything in.
Those are the placements that make two charts with the same Sun look nothing alike. Anyone born within a fortnight of you shares the Virgo Sun, and the great majority of them share the decan as well. The widget above will give you your own solar degree from your year, hour and birthplace, which is a narrower and more checkable thing than the category the date puts you in.
It also reports the distance to the nearest sign boundary, which on this date comes back as a comfortable margin rather than a close call. That number is worth seeing, because it turns a claim about a date range into a statement about a measured position, and it is the difference between being told which box you are in and being told where you stand inside it.
Questions people ask about this
Which decan is 14 September?
The third decan of Virgo, from twenty to thirty degrees, in every year. The Chaldean order gives that band to Mercury and the triplicity scheme gives it to Saturn.
What degree of Virgo is this birthday?
Between roughly twenty and seven tenths and twenty two and a tenth degrees at noon across the last century. Your year, time and place fix it more precisely.
Why is Mercury named twice for this birthday?
Because Mercury rules Virgo as a whole and the Chaldean count also assigns it the sign's final ten degrees. Tradition reads the repetition as concentration rather than as two separate influences.
Is 14 September close to Libra?
Not in any practical sense. The Sun does not leave Virgo until around 22 or 23 September, so more than a week of margin separates this date from the boundary.
Does the birth hour change the decan here?
No. Even the lowest years sit comfortably above twenty degrees at noon, and a day's solar motion is not enough to push a birth back across the line.
What does the date leave undecided?
The Moon sign, which has two or three possibilities, and the rising sign, which has twelve. Both need the birth time, and the rising sign needs the birthplace as well.