Equinox and solstice instants, 2024-2030
- An equinox or solstice is an instant, not a day - the Sun reaches an exact ecliptic longitude.
- The dates drift about six hours later each year, then jump back when a leap day is inserted.
- The tropical year measured equinox to equinox is about 365.2422 days, which is what the leap rule approximates.
Equinoxes and solstices, 2024-2030 (UTC)
| Year | March equinox | June solstice | September equinox | December solstice |
|---|---|---|---|---|
| 2024 | Mar 20 03:06 | Jun 20 20:50 | Sep 22 12:43 | Dec 21 09:20 |
| 2025 | Mar 20 09:01 | Jun 21 02:42 | Sep 22 18:19 | Dec 21 15:03 |
| 2026 | Mar 20 14:45 | Jun 21 08:25 | Sep 23 00:05 | Dec 21 20:50 |
| 2027 | Mar 20 20:24 | Jun 21 14:10 | Sep 23 06:01 | Dec 22 02:42 |
| 2028 | Mar 20 02:17 | Jun 20 20:01 | Sep 22 11:45 | Dec 21 08:20 |
| 2029 | Mar 20 08:01 | Jun 21 01:48 | Sep 22 17:37 | Dec 21 14:14 |
| 2030 | Mar 20 13:51 | Jun 21 07:31 | Sep 22 23:27 | Dec 21 20:09 |
March equinox to March equinox, measured (days)
| Interval | Days |
|---|---|
| 2024 → 2025 | 365.2465 |
| 2025 → 2026 | 365.2389 |
| 2026 → 2027 | 365.2354 |
| 2027 → 2028 | 365.2451 |
| 2028 → 2029 | 365.2389 |
| 2029 → 2030 | 365.2431 |
Why the time slips six hours a year
The tropical year is roughly 365.2422 days, about a quarter-day longer than a 365-day calendar. Each ordinary year the equinox therefore arrives about six hours later by the clock, and the leap day pulls it back by a full day. The table shows the sawtooth directly: three years of drift later, then a reset.
The measured intervals are not identical either. Earth's orbit is elliptical and perturbed by the Moon and the other planets, so consecutive equinox-to-equinox gaps vary by minutes. The 365.2422 figure is a mean, and the Gregorian leap rule - leap years divisible by four, except centuries not divisible by 400 - is a rational approximation to it accurate to about a day in three thousand years.
Equinox does not mean equal day and night
At the equinox the Sun's centre crosses the celestial equator, which would give exactly twelve hours of daylight for a point-like Sun and no atmosphere. Neither holds. Sunrise and sunset are defined by the upper limb rather than the centre, and refraction lifts the Sun's image above the horizon when it is geometrically below it, so day exceeds night by several minutes at the equinox. The date of true equal day and night, the equilux, falls a few days earlier or later depending on latitude.