Sixteen degrees, and why it holds
At noon in every year from 1930 to 2035 the Sun on 5 February has fallen between 15.5 and 16.9 degrees of Aquarius. A little over a degree of movement in a hundred and six years is a smaller spread than most people expect from a date.
The reason is the leap year cycle. The tropical year runs about a quarter of a day longer than a common calendar year, so the Sun appears roughly six hours further along on a given date each year until the leap day pulls it back. The two effects nearly cancel, and what is left is a drift of about a degree per century.
The widget above skips the noon assumption. Give it your year, hour and birthplace and it computes the actual position and reports how far it sits from the nearest sign boundary.
What that figure does not do is tell you the sign changed slowly. The Sun crosses a sign boundary at a specific instant, and the degree simply records how far past the last one you are. Sixteen degrees means about sixteen days into Aquarius and about fourteen from the end of it.
The upper half of the second decan
Decans are ten degree bands, three to a sign. Sixteen degrees is inside the second decan of Aquarius, past its midpoint and heading toward the twenty degree line where the third begins.
The Chaldean order assigns the second decan of Aquarius to Mercury, and the triplicity scheme gives it to Gemini, which is a Mercury sign, so both routes land on the same planet. The third decan above it takes the Moon in the Chaldean order and Libra under the triplicity scheme, which is a genuine disagreement, but on 5 February it does not arise: the position is comfortably short of the line in every year.
The habit of quoting a decan without its scheme is worth guarding against generally. If a source names a ruler for a decan and does not say which system produced it, the ruler cannot be checked. Naming both, as this page does, at least makes the disagreement visible where one exists.
What the tradition reads here
Aquarius is fixed air, ruled by Saturn in the older scheme and by Uranus since the modern one was adopted. Tradition reads the sign as principled and observational, more interested in the rule behind a case than in the case itself.
The Mercury decan is read as giving that abstraction a vocabulary, so the reading emphasises describing, comparing and setting out a position. Both of those are interpretations that the tradition carries and this page passes on as tradition. What is measurable is the degree, and that is stated separately for exactly that reason.
The parts still open
The Moon on 5 February has been in every sign across different years, and within a year it can change sign during the day, so an hour is normally required to pin it down. The Ascendant changes roughly every two hours and depends on the latitude of the birthplace as well as on the clock.
So a birthday settles the Sun and the decan and leaves the fast-moving material untouched. Anyone offering a full character reading from a date alone is working from one placement and filling in the rest.
What a date can support, beyond the Sun, is the slow moving material. The outer planets change sign over years, so their positions follow from a date alone. Everything faster needs the hour, and the angles need the birthplace as well.
Questions people ask about this
What sign is a 5 February birthday?
Aquarius. The date sits over two weeks past the Capricorn boundary and nearly two weeks short of Pisces, so there is no year in which it falls elsewhere.
What degree is the Sun on 5 February?
Between about 15.5 and 16.9 degrees of Aquarius at noon, taken across the last century. Your own figure depends on the hour and the year, and the widget above computes it.
Which decan is 5 February?
The second decan of Aquarius, in its upper half. Mercury rules it in the Chaldean order and the triplicity scheme assigns it to Gemini, which is also Mercury's.
How close is this date to the third decan?
Not close. The third decan begins at twenty degrees and the Sun on this date has never passed seventeen at noon in the modern calendar, so the boundary is three days of solar motion away.
Does the degree affect how the sign is read?
It affects the decan, which the tradition treats as a shading within the sign. It also decides which aspects the Sun makes to other placements, which is where the degree does most of its work.
Why do published Aquarius date ranges disagree?
Because the ingress moment shifts by hours from year to year and different sources round it differently. Only dates near the boundary are affected by that, and this one is not.