Thirds of a sign, and why they exist
Splitting each sign into three bands of ten degrees is one of the oldest surviving techniques in the tradition. The Egyptians used the bands to track time at night, and later Hellenistic and Arabic writers attached a planet to each one so that a position could be described more finely than by sign alone.
The scheme in common use follows the Chaldean order of the planets by apparent speed, running from Saturn out at the slow end down to the Moon. Applied across the zodiac from the first degree of Aries, that order puts the Moon in charge of the last third of Aquarius, which is where 10 February lands in every year.
What the tradition reads into a Moon decan
Aquarius is fixed air with Saturn as its classical ruler and Uranus as the modern one, and it is usually described as principled, sociable at a distance and resistant to being told what to think. The Moon subdivision is read as softening the outward edge of that, turning the sign's detachment toward memory, habit and the people already inside the circle rather than the cause outside it.
None of this is measurement. The degree is a fact you can check against an ephemeris, whereas the character attached to a decan is inherited interpretation, and different schools attach different characters to the same band. It is worth keeping the two apart.
The disagreement between schemes is itself useful information. Where two systems place different planets on the same ten degrees, the sensible conclusion is that the assignment is a convention rather than an observation, and that any reading built on it inherits that status.
The position barely moves
Across the century from 1930 to 2035, the Sun at noon on 10 February has stayed between roughly twenty and a half and twenty two degrees of Aquarius. The pattern is a slow forward creep of about a quarter of a degree per year, snapped back each time February gains a twenty ninth day.
So the useful answer to what degree am I is not one number but a narrow window, and your own year decides where in that window you sit. Someone born in a leap year sits near the low end, someone born in the third year after one sits near the top.
Anyone wanting the precise figure for their own birth should take it from a calculation rather than from a table of dates, since a table cannot resolve below the level of the sign.
Everything the date leaves open
The Moon covers between twelve and fifteen degrees a day, so on 10 February it spends part of the day in one sign and often part in the next. Your lunar sign therefore depends on the hour, not the date, and two people sharing this birthday can easily disagree on it.
The rising sign is fully open, since it depends on the exact minute and on how far north or south you were born. The widget above works out both from your own details along with the precise solar degree, and reports the distance from your birth to the nearest sign boundary.
None of this weakens the sun sign. It simply puts it in proportion, as one measured position among the several a full chart records.
Questions people ask about this
Is 10 February always Aquarius?
Yes. The Sun enters Aquarius around 20 January and leaves around 18 February, and this date sits comfortably inside that stretch in every year of the modern calendar.
What is a decan?
A ten degree division of a sign, so thirty six across the zodiac. Each one carries a planetary ruler in the older systems, which lets a position be described more precisely than by sign alone.
Who rules the third decan of Aquarius?
The Moon, under the Chaldean sequence. Some modern books instead assign it Venus by following the triplicity of the sign, so you may see the two schemes disagree.
Does the decan matter more than the sign?
It is a refinement rather than a replacement. The tradition treats the sign as the main statement and the decan as a qualification on it.
What degree is the Sun on 10 February?
Around twenty one degrees of Aquarius, varying by about a degree and a half across the last century. The widget above pins it down for your year and place.
Can two people born on this date have different charts?
Almost certainly. The Sun will agree to within a degree, and the Moon, the rising sign and every house cusp can differ completely.