A fixed sign between the markers
Aquarius holds the Sun from 300 to 330 degrees of ecliptic longitude. Neither end is a solstice or an equinox, which is what makes it a fixed sign in the seasonal scheme: it occupies the depth of a season rather than opening or closing one. In the north that means the middle of winter, roughly midway between the December solstice and the March equinox.
Without a named astronomical event to hold it in place, the published range varies more between sources than it does for the cardinal signs. Some lists print 20 January to 18 February, others 21 January to 19 February. Both are honest attempts at an average of a boundary that genuinely moves, and both fail anyone born within a day of an edge. The table above gives the real ingress time for a chosen year.
Still on the fast part of the orbit
Earth passes perihelion in the first days of January and is still travelling near its maximum orbital speed through the following weeks. That makes Aquarius one of the three brief signs, alongside Capricorn before it and Sagittarius before that, at somewhere around 29.5 days.
By comparison the Sun spends about 31.5 days in Cancer at the far end of the orbit. The arcs are equal, the crossings are not, and the gap between the two extremes runs to nearly two days. Watching the length column across the twelve signs is the quickest way to see the ellipse of the Earth's orbit in a table of dates.
Two rulers, and they disagree
Aquarius is air, and its classical ruler is Saturn, shared with Capricorn. Uranus was discovered in 1781 and modern practice reassigned Aquarius to it, usually retaining Saturn as co-ruler. The two produce noticeably different readings. Saturn gives the structural, principled, rule bound side of the sign; Uranus gives the disruptive and contrarian side. Both descriptions circulate, and the disagreement between them explains most of the contradictions people notice in sign write ups.
The phrase Aquarius season, meanwhile, is only a decade or so old in general use. It came from astrology on social media and means nothing more than the month the Sun spends there. It is a shared transit rather than a statement about anyone's natal chart, and its effect for you depends on which house Aquarius covers.
Edge birthdays and the view from the south
Births around 19 or 20 January and around 18 or 19 February are the ones most often assigned to the wrong sign, because the boundary can fall on either date and at any hour. There is no shared zone between two signs. The Sun is at a single longitude at every instant, and knowing your birth time plus the time zone that actually applied at your birthplace resolves it completely.
The dates are the same worldwide. The season is not. In the southern hemisphere Aquarius season falls in the middle of summer, not the middle of winter, which drains the seasonal logic out of the sign in a way the tropical system has never fully answered. The ingress times, being astronomical rather than climatic, are unaffected.
Questions people ask about this
When exactly does Aquarius season begin?
When the Sun reaches 300 degrees of ecliptic longitude, which usually falls on 19 or 20 January. There is no equinox or solstice at that point, so the calendar date drifts across the leap year cycle rather than being anchored. Enter a year in the table above for the precise moment.
Is Aquarius ruled by Saturn or Uranus?
By Saturn in traditional astrology and by Uranus in most modern practice, which commonly keeps Saturn as co-ruler. The two give different readings of the same sign, the Saturn one structural and the Uranus one disruptive, and neither has displaced the other.
Why does Aquarius take fewer than thirty days?
Earth reaches perihelion in early January and is still moving quickly through late January and February, so the Sun crosses the sign's thirty degrees in roughly 29.5 days. It is one of the three short signs, together with Capricorn and Sagittarius.
Is Aquarius a water sign?
No, despite the water carrier imagery and the name. Aquarius is an air sign, fixed in modality, and the figure in the symbolism is the person pouring rather than the water. The water signs are Cancer, Scorpio and Pisces.
Does the Age of Aquarius have anything to do with Aquarius season?
No. Aquarius season is a month of Sun transit that recurs every year. The astrological ages refer to precession, the slow wobble of Earth's axis that moves the equinox point backwards through the constellations over about 25,800 years. They share a name and nothing else.