Spring countdown

What the vernal equinox actually is

The vernal equinox is the instant when the Sun crosses the celestial equator. In the Northern Hemisphere it crosses going north, around 20 March, and astronomical spring begins. In the Southern Hemisphere the equivalent instant is around 22 or 23 September, when the Sun crosses going south and the day length starts climbing past 12 hours for southern observers. The same astronomical event marks spring in one hemisphere and autumn in the other, which is why this countdown uses the September equinox for southern visitors rather than the March one.

Why the date drifts a few hours each year

Earth completes a circuit around the Sun in about 365.2422 days, not a whole number. Each calendar year of 365 days falls about six hours short, so the equinox moves about six hours later in civil time. A leap year inserts a 24-hour February 29 and resets the drift, pulling the date roughly 18 hours earlier. Over a four-year cycle the equinox time wanders across the same calendar day or two, and Gregorian century rules trim the long-term residual. The exact UTC instants from 2026 onwards come from the US Naval Observatory's seasons data; for years outside that window this tool falls back to Jean Meeus's truncated approximation (Astronomical Algorithms, ch. 27), which is accurate to about a minute.

Astronomical spring vs meteorological spring

Climate offices in many countries peg spring to the first day of March (or September in the Southern Hemisphere) rather than the equinox. That convention is meteorological, not astronomical: it buckets the year into clean three-month blocks so seasonal statistics like temperature averages line up year to year. The astronomical definition this tool uses lines up with the planet's actual orbital geometry. Both are valid; meteorologists pick the tidier definition, astronomers pick the precise one.

Vernal equinox instants through 2030

These are the moments the countdown targets, listed in UTC. Northern Hemisphere visitors count toward the March column; Southern Hemisphere visitors toward the September column.

Read down either column and the roughly six-hour annual drift is plain, as is the leap-year snap-back between 2027 and 2028. In local time the calendar date can differ from the UTC date: the 2026 September equinox at 00:05 UTC, for instance, falls on 22 September for every clock west of Greenwich.

How the page picks your hemisphere

The toggle above starts from your device timezone. Zones that clearly belong to the Southern Hemisphere, such as Australian, southern African, and most South American zones, switch the countdown to the September equinox; everything else defaults to the March equinox. Timezones are political shapes rather than lines of latitude, so a device set to another region's clock can produce the wrong guess. The manual toggle fixes that instantly, and the countdown, arrival date, and local arrival time all update together.

Equal day and night? Close, but not exact

The word equinox promises equal night, yet on the equinox itself most places get several minutes more daylight than darkness. Two effects conspire. Sunrise and sunset are timed from the first and last glimpse of the sun's upper edge rather than its centre, and the atmosphere bends light around the horizon, lifting the sun into view while it is still geometrically below it. The date when day and night truly match, sometimes called the equilux, falls a few days before the March equinox in the Northern Hemisphere and a few days after it in the Southern, with the exact gap depending on latitude.

Countdown questions

Related tools

• Astronomical seasons 2026-2030 lists every equinox and solstice in both hemispheres alongside season lengths.
• Chinese 24 solar terms (jieqi) includes the vernal equinox as Chunfen, the fourth of the year's 24 solar markers.