Why the halfway point is noticed at all
A sign runs thirty degrees, so fifteen is its middle. That has a geometric consequence rather than a mystical one: bodies at the same degree of the four signs of a mode form exact squares and oppositions with each other, so the middle degrees of the fixed signs line up precisely across the chart.
Leo is fixed, along with Taurus, Scorpio and Aquarius. A Sun near fifteen degrees of Leo therefore stands close to an exact aspect with anything sitting at the same degree of those three, which is a checkable fact about chart geometry and not an interpretation.
Older material sometimes gathers the middle degrees of the fixed signs together and gives them a name. The grouping is descriptive of the geometry rather than of any influence, and the geometry is the half that can be checked.
Where the position falls
At noon across every year from 1930 to 2035, the Sun on 7 August has stood between roughly fourteen and about fifteen and a half degrees of Leo. The lower half of that window sits just short of the sign's centre and the upper half just past it, and the leap cycle decides which applies to a given year.
The hour of birth shifts it slightly in the same direction, since the Sun covers a little under a degree a day. None of that movement approaches a band edge or a sign boundary, so the only thing genuinely in play is whether the position sits before or after the halfway mark.
Still comfortably inside the second band
Ten to twenty degrees is the second of Leo's three divisions, and fifteen is its centre as well as the sign's. In the Chaldean sequence that band belongs to Jupiter, so a birth on this date sits at the deepest point of a Jupiter decan inside a solar sign.
Where a position near a band edge can reasonably be read with an eye on the neighbouring band, this one cannot. Whatever the tradition attaches to Jupiter in Leo applies here without hedging: warmth given room, a pull towards hosting and teaching, an appetite for the large gesture. That remains a convention handed down in the texts, and being at the centre of the band makes it unambiguous rather than stronger.
What the centre does not decide
An exact solar degree still describes one body out of many. The Moon crosses roughly half a sign in a day, so it can be in either of two signs on this date, and no page working from the calendar alone can say which.
The Ascendant turns through the whole zodiac between one midnight and the next and depends on the latitude of the birthplace as well as the clock. The widget above computes the exact solar degree for your own year and place, works out the Moon and rising signs from a birth time, and reports how far the birth stood from the nearest sign boundary.
The middle of a sign is worth knowing mainly because it is unambiguous. It removes any question about the sign and about the band, which leaves the chart as the only place a real question remains.
Questions people ask about this
Is the Sun exactly at fifteen degrees on 7 August?
Close to it, and either side depending on the year. The noon position runs from about fourteen to roughly fifteen and a half degrees of Leo, so some years fall short of the centre and others clear it.
What is significant about the middle degree of a sign?
It is a geometric fact rather than a mystical one. Bodies at the same degree of the four fixed signs form exact squares and oppositions, so a Sun there is aspected by anything at fifteen degrees of Taurus, Scorpio or Aquarius.
Which decan is 7 August?
The second decan of Leo, ten to twenty degrees, assigned to Jupiter in the Chaldean order. The position sits at or very near the centre of that band.
Does being mid sign strengthen the sun sign?
Not in any technical sense. A Sun at fifteen degrees is exactly as much in Leo as one at two. The degree matters for aspects and for house placement, not for whether the sign counts.
Is there any chance this date is not Leo?
None. The position is around the middle of the sign, about two weeks clear of the ingress on either side, so no year and no birth hour produces a different sign.
What do I still need a birth time for?
The Moon usually, since it can change sign inside the day, and the rising sign and houses always, because they depend on the exact minute and on the birthplace.