20 January to 18 February
The season occupies three hundred to three hundred and thirty degrees of ecliptic longitude. In date terms it opens on 19 or 20 January and closes on 18 or 19 February, and its closing ingress is the earliest in its month of any on the wheel.
Both edges alternate between two dates. The cause is arithmetic: a tropical year runs about six hours longer than a calendar year, so a crossing arrives later for three consecutive years and then jumps back roughly eighteen hours when February is given an extra day.
A fixed sign in the middle of winter
Aquarius sits between the December solstice and the March equinox and contains neither, which is the defining position of a fixed sign. In the northern hemisphere the Sun's declination climbs steadily through the month and daylight lengthens fastest towards the end of it.
The cross quarter point at the start of February corresponds to about fifteen degrees of Aquarius, the exact midpoint of the northern winter, and the festivals held around that date belong to the same seasonal arithmetic. That is calendar history rather than a statement about anyone born then.
Two rulers, one traditional and one modern
Saturn holds Aquarius in the classical scheme, sharing the sign with Capricorn. Uranus was added after its discovery in the late eighteenth century, and most modern texts use both, which is worth stating plainly as a later revision rather than an inherited part of the system.
Aquarius has no traditional exaltation. Its decans fall to Venus, Mercury and the Moon, so the three ten degree bands of the season are governed by the fastest and gentlest of the classical bodies.
Where the calculation takes over
A range printed on a poster stops being useful within about two days of either edge, because it was rounded to whole dates and the ingresses never fall on whole dates. The year, the clock time and the birthplace give the solar longitude directly, and it lies in one sign.
Sidereal charts move the season on by roughly twenty four degrees, a little over three weeks, since they count from the stars rather than from the equinox and precession has separated the two anchors over the past two thousand years. Most tropical Aquarius births read as Capricorn in that frame.
Questions people ask about this
What are the Aquarius dates?
Approximately 20 January to 18 February. The exact start falls on 19 or 20 January and the end on 18 or 19 February, varying with the year and with the time zone the birth is dated in.
Why do the dates change from year to year?
Because the tropical year is not a whole number of days. The ingress slips about six hours later each year and is pulled back by each leap day, so it oscillates across roughly a day and a half.
When is Aquarius season this year?
Within the range above, at a minute that has to be calculated for the specific year. Anyone born close to either edge needs the actual solar position rather than a table.
Why does Vedic astrology not make me Aquarius?
It measures from the fixed stars rather than from the equinox, and the two references have separated by about twenty four degrees. That moves every sidereal boundary later by a little over three weeks.
Does being born on the first day of Aquarius mean anything special?
It puts the Sun in the first degree of the sign, which matters for aspects and house placement. The tradition does not read it as a weaker or stronger version of the sign itself.