The centre of the sign
Each sign spans thirty degrees, so fifteen is the middle. At noon across 1930 to 2035 the Sun on 4 February has stood between 14.5 and 15.9 degrees of Aquarius, straddling that midpoint.
The Sun covers roughly one degree a day, so being fifteen degrees into a sign means being about fifteen days past the entry and fifteen short of the exit. There is no arrangement of year, hour or time zone that moves a fortnight, which is why this date is one of the few where a sun sign can be stated without any caveat at all.
It is a useful position for another reason. Because the Sun is a fortnight from either boundary, a reader with no birth time, an uncertain time zone and only a rough memory of the year still gets the same answer. Very few astrological questions are that robust to missing information.
Why boundary distance is worth reporting
Most sun sign errors come from the same source: a birth close to an ingress, a birth time that was never recorded, and a time zone that was applied wrongly or not at all. All three matter only in proportion to how near the boundary you are.
At fifteen degrees the margin is enormous. A whole day of error in the birth time moves the Sun by one degree, and a whole century of calendar drift moves it by about the same. The widget above reports the distance to the nearest boundary alongside the degree, and on this date it will come back with a comfortable figure.
This is also why mid sign dates rarely generate the arguments that boundary dates do. Nobody born on 4 February has ever been told they might be a Capricorn. The confusion in birthday astrology is concentrated almost entirely in the two or three days either side of each ingress.
The decan sitting under it
Fifteen degrees is the middle of the second decan as well as the middle of the sign, since that band runs from ten to twenty. The Chaldean order gives it Mercury. The triplicity scheme gives it to Gemini, a Mercury sign, so the two schemes agree, which they do not for most decans.
Aquarius itself is fixed air, assigned to Saturn traditionally and to Uranus in modern practice. Tradition reads the sign as observational and rule-minded and reads the Mercury band as tilting that toward description and exchange. That is what the tradition says about the position, offered as such.
Certainty about one thing only
The confidence available here applies to the Sun and stops there. The Moon changes sign every two and a half days or so and can do it partway through 4 February, so the hour is usually needed. The Ascendant turns through all twelve signs in a day, so it depends on the minute and the latitude, and the houses depend on the Ascendant.
A date at the centre of a sign gives you the most certain possible answer to the least specific possible question. That is a fair trade as long as it is stated plainly.
The degree is still useful even when the sign is obvious. It decides which aspects the Sun makes to the other placements in a chart, since aspects are measured in degrees rather than in signs, and two Aquarius Suns ten degrees apart can have quite different aspect patterns.
Questions people ask about this
What sign is 4 February?
Aquarius, at about the midpoint of the sign. It sits roughly fifteen days after the Capricorn boundary and fifteen before the Pisces one, so no year or birth time affects it.
What does fifteen degrees of a sign mean?
It is the exact middle of the thirty degree span. The Sun moves about a degree a day, so a Sun at fifteen degrees is about halfway through the sign's season.
Do I need my birth time or time zone for this date?
Not for the sun sign. Time zone errors shift a position by hours at most, and this date is a fortnight from the nearest boundary. You still need both for the Moon and the Ascendant.
Which decan does 4 February fall in?
The second decan of Aquarius, ten to twenty degrees, and near its centre. Mercury rules it in the Chaldean order and Gemini holds it under the triplicity scheme.
Is a mid sign Sun stronger than one near a boundary?
Not in the technical sense. A Sun at one degree is as much in the sign as one at fifteen. The degree matters for aspects and for house placement, not for whether the sign counts.
What does the widget above add if the sign is certain?
It gives the exact degree for your year, hour and birthplace, names the decan and both of its rulers, and states how far you were born from the nearest sign boundary.