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Equinox and solstice boundary times in UTC for both hemispheres, with the current astronomical season and countdown to the next boundary.
Next boundary: Autumn starts in 69 days.
Astronomical seasons start at the exact instants of the two equinoxes and two solstices. In the Northern Hemisphere, spring begins at the March equinox, summer at the June solstice, autumn at the September equinox, and winter at the December solstice. The Southern Hemisphere uses the same four events with opposite season names: March starts autumn, June starts winter, September starts spring, and December starts summer.
These dates are not the same as meteorological seasons, which start on the first day of March, June, September, and December for easier climate statistics. Astronomical boundary times shift by several hours each year because Earth does not complete its orbit in an exact whole number of calendar days. Leap years pull the pattern back, then the drift resumes.
The table above uses UTC timestamps from the US Naval Observatory Earth's Seasons data service for 2026 through 2030. Durations are measured from one boundary instant to the next, so they are fractional days rather than rounded calendar-day counts.
Source: US Naval Observatory Earth's Seasons.
Run the subtraction on the 2026 boundaries and the four seasons come out unmistakably unequal. Northern Hemisphere spring 2026 runs from the March equinox at 14:46 UTC on 20 March to the June solstice at 08:24 UTC on 21 June: 92.73 days. Summer then stretches 93.65 days to the September equinox, autumn lasts 89.86 days, and winter is the shortest of all at 88.98 days. The same four intervals apply south of the equator with the names swapped, so southern summer is the 88.98 day season and southern winter the 93.65 day one.
The imbalance comes from the shape of Earth's orbit. The path is slightly elliptical and Earth passes closest to the Sun in early January, where it moves fastest. The quarter of the orbit containing that point gets covered quickly, which compresses the season in progress, Northern Hemisphere winter, and stretches the opposite one. Nearly five days separate the longest and shortest seasons of the same year.
Every instant in the table is one worldwide moment; only its clock label changes. To localise a boundary, apply your UTC offset for that date, remembering that daylight saving can change the offset. Take the December solstice of 2026 at 20:50 UTC. In Los Angeles (UTC-8 in December) that is 12:50 in the afternoon on 21 December. In Sydney (UTC+11 during its daylight saving period) the same instant lands at 07:50 on the morning of 22 December, a different calendar date. Events late in the UTC day often cross midnight somewhere, so check the day as well as the hour.
A few details in the data reward a closer look. The March equinox stays on 20 March in UTC across all five years, but its time of day walks forward by five to six hours each year, from 14:46 in 2026 to 20:25 in 2027, before the leap year 2028 drags it back to 02:17. The September equinox slips from 23 September in 2026 and 2027 to 22 September from 2028 onward. And 2028 is the only year in the window with a 20 June solstice, at 20:02 UTC, again a leap-year effect. None of this is drift in Earth's orbit; it is the calendar breathing around a year of about 365.2422 days.
Earth's orbital speed varies. It moves fastest near its early-January closest approach to the Sun and slowest near its early-July farthest point, so the seasons surrounding January pass more quickly than the ones surrounding July.
Yes. An equinox or solstice is a single orbital instant. The table lists each one twice only because the season it starts differs by hemisphere: the March equinox opens northern spring and southern autumn simultaneously.
It carries the most daylight almost everywhere in the Northern Hemisphere, but because the solstice is an instant rather than a day, timezone offsets can occasionally place a location's longest local day one calendar day away from the printed date.
It lists only boundary times checked against the US Naval Observatory data service, and that verified set currently covers 2026 through 2030. Nothing unusual happens afterwards; the drift and leap-year pattern simply continues.
Each boundary is given to the minute in UTC, matching the precision published by the US Naval Observatory for these years. Minute-level precision is far finer than any everyday planning requires.