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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: Summer starts in 3 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.