Astronomical seasons, 2026-2030

How astronomical seasons are defined

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.

Season lengths, worked through for 2026

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.

Turning a UTC boundary into your local clock

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.

Patterns inside the 2026-2030 window

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.

Equinox and solstice questions