Thirty degrees is a wide box
Calling someone Virgo says the Sun was somewhere in a thirty degree stretch of the ecliptic. That is a large space. A Sun at one degree and a Sun at twenty nine degrees of the sign make completely different aspects, fall on different sides of every midpoint, and in traditional terms carry different faces and different terms.
Sign level description ignores all of it, which is why so much of it reads as generic. It has to cover the whole box, so it says only what is true of the entire box.
The face this date falls in
The first cut is into three faces of ten degrees. On 30 August the Sun stands between about 6.2 and 7.6 degrees of Virgo at noon, depending on the year, so the seventh degree is the usual answer and the first face is certain. That band runs from the start of the sign to ten degrees.
Rulership of it depends on the tradition consulted. The Chaldean loop of Mars, Sun, Venus, Mercury, Moon, Saturn and Jupiter, counted from the start of Aries, arrives at the Sun. The triplicity method walks the earth signs in the order Taurus, Virgo, Capricorn and hands Virgo's first face back to Virgo, under Mercury. Both are long established and they are not reconcilable, so it is worth knowing which one a description rests on.
What that means in practice is that a good deal of contradictory decan writing is not contradictory at all. Two authors describing the same ten degrees very differently are usually reporting two schemes rather than disagreeing about the sky.
What the tradition reads into it
Virgo itself is treated as mutable earth, careful, corrective and attentive to how things actually work. Applied to the opening face with a solar ruler, the traditional reading adds a note of plain visibility, the sign doing its work in the open rather than behind the scenes. Under the Mercury reading the same band is described as the sign at its most characteristic, the analytical streak undiluted.
These are interpretations of an old system and should be taken as such. What they are not is arbitrary, because they attach to a measured band of longitude that either contains your Sun or does not.
Beyond the decan
Finer distinctions exist. Traditional astrology also divides each sign into unequal terms or bounds, five per sign, and reads planets by degree within them. Modern practice leans instead on exact aspects, which need the longitude to the minute rather than to the degree.
All of that still concerns one body. The Moon on 30 August is in one of two signs depending on the hour, the Ascendant can be any of the twelve, and the houses follow from the Ascendant. If the aim is to distinguish yourself from everyone else born on this date, the birth time does far more work than the decan does. The widget above takes both the date and the time.
None of these layers is exclusive. A traditional reading uses the sign, the face and the term together, and a modern one leans on exact aspects instead, but both need the longitude before they can begin.
Questions people ask about this
What decan is 30 August?
The first decan of Virgo, which covers the sign's opening ten degrees. The Sun on this date sits near seven degrees, so it is late in the face but not close to leaving it.
How is a decan different from a sign?
A decan is a ten degree third of a sign, so each sign has three and the zodiac has thirty six. Each carries its own planetary ruler, which layers a second influence over the sign's own in traditional reading.
Which decan ruler should I use?
Whichever the description you are reading assumes. The Chaldean order gives Virgo's first face to the Sun, the triplicity order gives it to Mercury. Neither has authority over the other and older texts more often mean the Chaldean one.
Is 30 August ever not Virgo?
No. The Sun entered Virgo about a week before and stays until late September, so no year or birthplace moves this date out of the sign.
What exact degree will the widget give me?
A figure between roughly 6.2 and 7.6 degrees of Virgo, computed to minutes of arc from your year, hour and place, along with how far that sits from the nearest boundary.
Do decans predict anything?
No. They are a traditional layer of description applied to a measured band of longitude. Nothing in the scheme forecasts events, and a reputable reading marks the interpretive part as interpretation.