Two years out of a hundred and six
Zero degrees of Libra is the September equinox, the crossing where the Sun moves south over the celestial equator. Through the period covered here it lands on 22 or 23 September, and at noon on the twenty second it has usually not yet happened. The exceptions are the two years where it came early enough to beat midday.
The drift is ordinary arithmetic. A tropical year exceeds the common calendar year by close to a quarter of a day, so an equinox arrives around six hours later each year until a leap day pushes it back by roughly eighteen. Followed across ten years the crossing sweeps through about a day and a half, which is exactly enough to catch this date once or twice per century as the whole pattern slides slowly earlier.
The hour, the place, and a boundary that lands mid day
In the years where the equinox falls on the twenty second, it does so at a particular hour, and births either side of that hour are different signs. That makes birth time a real factor here rather than a formality. Without it, a calculation has to default to noon, and noon is precisely where the argument is.
Birthplace does the rest. The equinox is one instant for the whole world and only local clocks differ, so a crossing at 02:00 UTC on 23 September is still ten in the evening on the twenty second in New York. A birth late in the evening in the Americas can be Libra while the same clock reading in Europe is still Virgo. That single mismatch produces more wrong sun signs than any other cause. The widget above resolves it and tells you how many hours from the crossing you were born.
Why the cusp idea fails here
The Virgo Libra cusp is described as fastidiousness softened by charm. The sky offers no version of that. At every instant the Sun has one ecliptic longitude, and the equinox is the line between under three hundred and sixty degrees of the old cycle and past zero degrees of Libra. Ten minutes before it you are entirely Virgo. Ten minutes after, entirely Libra.
The honest use of the word is as a flag on incomplete data. Someone knew your date and not your year, hour or city, so they described both possibilities at once. Nothing about the sky is uncertain, only the record. Fill it in and the cusp disappears.
Virgo and Libra, and the shorter autumn signs
Virgo is mutable earth ruled by Mercury, read as exacting, useful and attentive to detail. Libra is cardinal air ruled by Venus, read as comparative, socially aware and concerned with balance. No element and no modality is shared, and mutable turning to cardinal is where refining becomes initiating.
One further point is specific to this half of the year. The Sun is speeding up as it moves towards perihelion in early January, so the autumn and winter signs are traversed faster than the summer ones and run closer to twenty nine and a half days. That makes the boundaries here slightly more mobile relative to the calendar than the ones in June or July. Whichever side you land on, the rest of the chart is untouched. The Moon, the Ascendant and every planet stay where they were.
Questions people ask about this
Is 22 September Virgo or Libra?
Virgo in a hundred and four of the years from 1930 to 2035, taken at noon, and Libra in two of them. The widget above settles which group your year, hour and birthplace put you in.
Does Libra start at the equinox?
Yes. In tropical astrology zero degrees of Libra is defined as the point where the Sun crosses the celestial equator moving south, so the equinox instant is the ingress itself.
Why is my birth time important on this date?
Because in the rare years where the equinox falls on the twenty second, it happens at a specific hour. A morning birth and an evening birth on that same day are different signs.
Am I on the Virgo Libra cusp?
No, because nothing occupies the space between two signs. The Sun sat at one longitude when you were born and it lay inside one of them. Cusp is shorthand for details nobody had.
Are autumn signs shorter than summer ones?
Slightly. The Sun accelerates as it approaches perihelion in early January, so it passes through the autumn and winter signs in nearer twenty nine and a half days than the thirty one the summer signs can take.
Does being born close to the crossing weaken the sign?
Not technically. A Sun at zero degrees of Libra is as much in Libra as one at eighteen. The degree governs aspects and house placement rather than whether the sign is in force.